PLSOIL 120
ORGANIC FARMING AND GARDENING

GUIDE FOR FERTILIZATION OF HORTICULTURAL CROPS


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CHAPTER 9

PRACTICES FOR FERTILIZATION

By the time that symptoms of nutrient deficiencies appear, damages to plant growth and quality have occurred. Corrections of the problems created by the deficiencies often cannot be made, even if the deficiencies are diagnosed quickly and accurately. To avoid the problems of the development of deficiencies and the uncertainties of being able to make corrections, most growers try to provide crops with adequate nutrition through fertilization before symptoms develop. Soil testing is used to assist growers in fertilization. A soil test taken when land is entered into cultivation will give an assessment of the initial fertility of a soil and allow for formulation of recommendations for a specific plot of land.

Soil tests are important for adjusting practices as fertility of the soil is built up through fertilization and management (see Chapter 5). In general, recommendations for nitrogen applications are not adjusted, but recommendations for phosphorus and potassium fertilization may be reduced by one-third or more as soil fertility is raised from low to high as assessed by soil tests. Recommendations for nitrogen fertilization may be adjusted according to whether green manures have been turned under and according to previous fertilization and cropping history of the land.

Often practices of fertilization are based on knowledge of the amount of nutrients that are removed by crops and adding these amounts annually to replenish the fertility to the soil. Also fertilization is based on year-to-year observations of plant growth which result in general recommendations for application of nutrients in the absence of soil tests. The following practices relate to methods of fertilization that may be employed in the absence of other guidelines.

Fruit Crops

Apples, Pears, Cherries, and Peaches

For maximum productivity of fruit trees, the physical properties of soils are more important than nutrient levels in soils. Selection of the site for planting is a very important factor in production of fruit crops. Fruit trees will produce over a wide range of fertility if the soil is deep and well drained for root development. In wet soils, where exchanges of gases is limited, restricted rooting will limit tree growth and fruit production. Problems of mineral nutrition of trees usually can be corrected, but little can be done to correct poor physical properties of a site. Recommendations for fertilization consider that the physical properties of a site are acceptable for crop production.

Soil tests are unreliable for determining the nutrient requirements of fruit trees. Collection of a representative sample of the soil, particularly with respect to depth occupied by the roots is a problem in soil testing with these crops. Correlation between soil tests and performance of trees is poor for virtually all plant nutrients. Measurements of soil pH are useful, but again the problem of collecting a representative sample is present. Generally, at soil pH 6 to 7, nutrient availability to trees is maximized.

Fertilization will vary with soils, ages of trees, species and cultivar, fruit load, and other conditions of the trees. Growers observe tree growth and production and quality of fruits from season to season and adjust the amounts of fertilizer applied accordingly. Large changes in the amount of fertilizer applied should be avoided. Trees should be evaluated for visual symptoms and growth responses before and after fertilization. Trees making 6 to 12 inches of growth per year and maintaining healthy green leaves are adequately nourished. The nutrient concentrations in leaves of fruit trees is correlated relatively well with yield and quality of fruits. Expert advice should be sought for sampling and handling of leaves, for analysis of samples, and for interpretation of analyses. Growers should consult specialists in fruit production in the agricultural extension service, other growers, or dealers for assistance in sampling, analyses, and interpretation of results.

Isolated or widely spaced trees should be fertilized individually. In dense plantings, roots of trees may overlap, and fertilizer may be applied in broadcast applications over the orchard. Time of application of fertilizers except for nitrogen is not important. Nitrogen should be applied after complete dormancy up until bud break in the spring. Late fall applications of nitrogen are convenient. The roots of the trees will intercept nitrates so that leaching is not a problem. In addition, most orchards have a grass sod or a fall-planted cover crop that will intercept nitrates. Fall application of nitrogen permits the nitrate to leach below the root system of the grasses so that it is available to the trees.

Nitrogen has more effects on quality of tree fruits than other nutrients have. Low nitrogen can cause poor flower bud development. Weak flowers may fail to set fruits. Fruits of nitrogen-deficient trees may be small so that yields are less than those of trees with adequate nutrition. Quality of fruits with respect to color and storage may not be affected by nitrogen deficiency. Excessive nitrogen may give higher yields but lower quality of fruits than underfertilization. Signs of excessive nitrogen are poor color, softness, and short storage life of fruits and excessive vegetative growth (12 to l8 inches per year). Trees with nitrogen deficiency, with excess of nitrogen, or with nitrogen applied before dormancy, may be susceptible to winter killing.

Trees do not seem to have any preference for nitrogen in one form or another. The total amount of nitrogen applied per tree is the important factor in nitrogen fertilization of fruit crops. Urea, ammonium nitrate, calcium nitrate, and nitrogen from multinutrient fertilizers (5-10-10, 10-10-10) are used successfully. Accumulation of ammonium nitrogen in the soil restricts calcium accumulation by plants, and if a choice is to be made, nitrate forms would be preferred. Ammonium fertilizers acidify the soil, whereas nitrate fertilizers have no effect on soil pH or raise the pH slightly upon absorption by plant roots. Calcium nitrate will provide two key nutrients, calcium and nitrogen. Farm manures can be used as a source of nitrogen, but their use is not a common practice. Organic matter in an orchard soil is maintained by use of sods or cover crops or decaying mulches. Large application of manures may promote fire blight disease (Erwinia amylovora) of apple. Slow-release fertilizers, such as manures, encourage late growth of twigs and late development of fruits, resulting in competition between vegetative growth and fruit production in the current year and flower bud development in the following year. Late growth of twigs may be the cause of the increase incidence of fire blight with manures.

The evidence is weak as to whether fruit trees respond to fertilization with phosphorus. So, using a mixed fertilizer containing phosphorus may be a waste of phosphorus and money. Individual trees or orchards are fertilized by broadcasting materials on the soil surface in a circle around the trees. Phosphorus is unlikely to move deeply enough in the soil to nourish tree roots. Applications of phosphorus are made generally to fertilize the sod in apple orchards or cover crop, if any, in peach orchards.

Potassium is needed for fruits to have good color, shape, and size. Optimum fertilization with potassium is higher than what the tree will remove in order to ensure that adequate potassium reaches the tree roots. The potassium fertilizers must be applied to the soil surface, and leaching is required to move the potassium to the roots. Above-optimum fertilization gives no further improvement in fruit quality. Potassium chloride is the most commonly used source of potassium. If applications are high (above 600 lb/acre or 15 lb/1,000 sq ft or 4 or 5 lb per tree), potassium sulfate or potassium phosphate is recommended sometimes, because of their lower solubilities. It is unlikely that differences between potassium fertilizers would be apparent at lower levels of fertilization. Use of potassium nitrate to supply potassium to trees would result in excessive applications of nitrogen. Potassium magnesium sulfate would be a good choice as it supplies three essential elements.

Suggested nitrogen, phosphorus, and potassium fertilization of average trees is presented (Table 35). For heavily bearing trees, applications of potassium should be at the high end of the range. Nitrogen application may be held low with heavily bearing trees unless the trees show stresses of nitrogen deficiency. Fertilization with nitrogen from 0.1 to 0.6 lb/tree should be a rigid practice with young, unbearing, or small trees to promote growth. This application is based on 0.1 lb N/year of tree age. Fertilizer should be applied on the nonbearing trees in spring (April to May) depending on climate. Do not fertilize newly planted trees until their leaves come out. Large, mature apple trees may not require annual fertilization with nitrogen if they make 6 to 12 inches of growth per year and if their leaves are green with no signs of yellowing. Trees overfertilized with nitrogen may produce large yields of soft, green fruits that have poor handling and keeping qualities. Bearing trees making 18 inches of growth per year may be showing signs overfertilization with nitrogen, although 12 to 18 inches of annual growth would be desirable with nonbearing trees. Peach trees require nitrogen fertilization each year to maintain vigorous growth of about 12 inches per year. A section of peach branch produces leaves only in the first year and fruit only in the second year. Yearly production of peaches requires demands a yearly production of new, vigorous shoots. Apple fruits are produced from long-lived spurs on the branches. Peaches require overall a more fertile soil than apples. As a rule, pear, plum, and cherry trees can be fertilized in the same way as apple trees--or perhaps with pears, a little less fertilizer than with apple trees.

 

Table 35. Suggested annual fertilization of average standard fruit trees

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Age & condition of tree

Amount of fertilizer to apply, lb/tree

N

P205

K20

Young, nonbearing

0.1 to 0.6z

0.3

1.3

Bearingy

0 to 0.3x

0.3

1.3 to 4.3w


zAfter planting and after soil has been firmed around root mass, apply nitrogen at 0.1 lb/tree in first year.
In following years, apply 0.1 to 0.2 lb /tree to produce shoot growth of 12 to 18 inches/year.

yApply boron at 0.5 oz per tree.

xApply enough nitrogen to maintain shoot growth of 6 to 12 inches/year.

wFor yields of less than 15 bu/tree, apply 1.3 lb; for 15 to 25 bu/tree, proportionally increase to 2.7 lb/tree;
for more than 25 bu/tree, increase gradually to 4.3 lb/tree.

_______________________________________________________________

 
The feeding roots of large fruit trees are in a zone 2 to 3 ft deep in the soil and about half way between the trunk and dripline. Application of fertilizers should be in a limited area starting at about 1 foot from the trunk with nonbearing or small trees and at about 3 feet with large bearing trees and ending well before reaching the dripline. Fertilizers applied in alley ways do no good. However, in home gardens, fertilization of lawns around trees usually provides adequate nutrition without the need of additional treatment of the trees. If the grasses or weeds under a tree appear nitrogen-deficient, even in an orchard, fertilizer is probably needed.

Calcium deficiency produces many disorders in apple production. Calcium deficiency rarely if ever occurs on vegetative growth under field conditions but is a known problem affecting fruit quality. Bitter pit, scald, and internal breakdown of fruits are associated with low calcium in fruits or with imbalances of calcium with other cations in fruits. A reliable method of increasing calcium in fruits through fertilization has not been developed. Calcium in fruit is not well correlated with calcium in soil or leaves, but if disorders appear on fruits, growers should consider all means of increasing calcium in fruits, including liming with high-calcium limestones, fertilizing with calcium nitrate, and spraying of foliage with calcium chloride--even dipping harvested fruits in calcium chloride. The problem with calcium entering apples appears to exist with the movement of calcium through the stem of the fruits and into the flesh. Foliar applications of calcium fertilizers may give partial but not full control of disorders in fruits. Postharvest dipping of apples in solutions of calcium chloride has been used commercially to increase calcium in fruits. For nourishment of nonbearing trees, limestones are the main source of calcium.

Magnesium deficiency may appear on foliage of trees in acid soils. Soil depletion of mangesium is associated with low pH. Magnesium is provided by adjusting pH with dolomitic limestones or fertilizing with potassium magnesium sulfate.

Except for boron, minor element defiencies are infrequent problems in tree fruit production. Boron deficiency in apples and peaches may cause crop failure. Apple fruits may drop preharvest and be corky. Peach fruits may be gummy, mealy and tasteless or corky in the center. In extreme cases, shoot dieback and oozing may occur, or trees may die. Boron can be applied as foliar sprays (water-soluble sodium pentaborate) in the early season (tight cluster to pink/white bud stage or a week after petal-fall) at 2 lb B/acre (prepared as 1 lb B/100 gal spray solution). Boron fertilizer may be mixed with applications of pesticides but not with calcium or magnesium sprays (insoluble salts of calcium or magnesium borate are formed). Soil applications should be 2 lb B/acre every year or every third year, depending on the severity of the deficiency. Boron for direct soil use is available as soluble borax or borate fertilizers or as a boron-enriched commercial fertilizer (e.g., 10-10-10-WB). Soil application is more effective than foliar spraying to increase boron in fruits. Boron is a toxic element, and too much can be as bad as too little. Recommended amounts and frequencies of application should be followed strictly. Foliar analysis is used as a guide by commercial growers. A sufficient level of boron in leaves of tree fruits, as in most cultivated crops, is around 30 ppm (mg/kg).

Small Fruits

Strawberries (Table 36). Strawberries will tolerate a soil acidity range of pH 5.5 to 6.5. Beds for planting should be prepared with fertilization with 0.5 lb N - 1 lb/P2O5 - 1 lb K2O per 1,000 sq ft (20-40-40 lb respectively of each nutrient per acre) to start the plants. This fertilization can be satisfied with 10 lb of 5-10-10 per 1,000 (1 lb/100 sq ft). The fertilizer should be well mixed in the bed before planting. After 3 or 4 weeks from planting and again in August, sidedressed applications of fertilizer should be made. Individual, surface-applied, sidedressed (bands near the plants) applications of 4 to 6 lb of 5-10-10 fertilizer per 25 feet of row (about 100 sq ft of total ground area including space between rows) will provide the correct amount and ratio of nutrients at each time of fertilization (about 2 to 4 lb N - 4 to 6 lb/P2O5 - 4 to 6 lb K2O per 1,000 sq ft). Use only half as much 10-10-10, for the nitrogen is the important element to control. With conventional cultivars, bearing is in the second year. If the harvest is good, consider keeping the plants for one additional season. Fertilize these plants immediately after harvest and again in August with 4 to 6 lb of 5-10-10 per 25 ft of row.

 

Table 36. Recommended average fertilization of small fruit plantings.

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------------------------Fertilization (lb/1,000 sq ft of bed)z--------------------------

-----------Year of planting-------------

--------------Bearing years--------------

Type of fruit

N

P2O5

K2O

N

P2O5

K20

Strawberry

0.5

1.0

1.0

3.0

5.0

5.0

worked in before planting

sidedressed after harvest & in August

Raspberry

0.5

1.0

1.0

3.6

7.0

7.0

worked in before planting

broadcasted in early spring

Grape

0.15

0.3

0.3

2.0

4.0

4.0

broadcasted

broadcasted

Blueberry

See Table 37

See Table 37


 zExample for fertilizer application: to apply 0.5 lb N, 1.0 lb P2O5, and 1.0 lb K2O use 10 lb 5-10-10 per 1000 sq ft.

____________________________________________________________________________________________

 

Bramble Fruits: Raspberries and Blackberries (Table 36). These plants will grow in wide range of pH in acid soils. Prepare the beds in the same manner as with strawberries (10 lb 5-10-10 per 1,000 sq ft) in the spring of the year of planting. Apply no additional fertilizer in this year. In the following years, fertilize in early spring with broadcasted application of 6 to 8 lb of 5-10-10 (half this amount of 10-10-10) per 25 ft of row (3 to 4 lb N - 6 to 8 lb P2O5 - 6 to 8 lb K2O per 1,000 sq ft of plot area). Do not fertilize raspberries in the summer, for young, succulent growth stimulated by the nitrogen in the fertilizer will increase susceptibility of canes to winter killing.

Grapes (Table 36). Soil should be conditioned for 2 years before planting by additions of organic matter from composts, farm manures, or green manures. The soil should be fertile in nutrients, 3-to 4-feet deep, and well drained. The surface should have good air drainage, that is, cold air should move down slope. Slope should south-facing if possible to give warm soil and air. A soil pH of 6 to 7.5 is desirable, especially for European cultivars. After planting of vines in the spring, about 4 to 6 oz of 5-10-10 should be scattered on the soil surface outward from at least 12 inches from the vine. In subsequent years, this amount should be doubled until 3 to 4 lb of 5-10-10 or equivalent are applied annually per vine. The equivalent fertilization should be adjusted according to the amount of nitrogen in the fertilizer (for example, apply half as much 10-10-10; about one-tenth as much urea, 46% N).

Blueberries (Table 37). Blueberrie plants should be grown in strongly acid soils (pH 4.5 to 5.5). These plants are in the family, Ericaceae, often referred to as acid-loving plants. In soils with pH higher than 5.5, iron deficiency may be a problem. This condition is sometimes called lime-induced chlorosis, because the iron in the soil is too insoluble, unavailable, for the plants to absorb at alkaline pHs. Turning under a green manure crop one year before planting will increase soil acidity. Soils can be acidified with applications of organic matter (1 lb per sq ft of land) worked into the soil. Sawdust mulches help to maintain acidity. Fertilization with ammonium sulfate also will maintain acidity, but do not use this material on plants that are less than 3 years old because of the possibility of ammonium toxicity. Blueberries may need only a nitrogen fertilizer applied in the spring; however, a multinutrient fertilizer (5-10-10 or 10-10-10) will give as good results and maybe better than nitrogen fertilizer alone. Nitrogen in dry mixed fertilizers will be largely from an ammoniacal source--urea, diammonium phosphate, or ammonium nitrate. No lime is applied to blueberry plantings. The amount of fertilizer that is applied to blueberries increases with age of the plants. The following example (Table 37) can be considered as a guide for fertilizing highbush blueberry plantings with fertilizers of varying composition (5% to 34% N). Note that nitrogen is the factor that determines the amount of fertilizer that is applied.

Newly set plants should not be fertilized until 4 weeks after transplanting. The 1 lb of 5-10-10 or equivalent of other fertilizers should be spread around the plant beginning about 1 foot from the plant. Fertilization in the following years should be as soon as the ground thaws, again with the fertilizer being kept about a foot away from the base of the plant.

 

Table 37. Examples of amounts of fertilizers to apply to blueberry plantings of differing ages (Recommendation courtesy of Massachusetts Cooperative Extension, Amherst, Mass).

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Kind of fertilizer

---------------------------------Year after planting--------------------------------------

0

1

2

3

4

5

6

7+

----------------------------------------lb/plant------------------------------------------

5-10-10

1

2

4

6

8

12

14

16

10-10-10

0.5

1

2

3

4

6

7

8

Ammonium sulfate (21% N)

0.2

0.4

0.8

1.2

1.6

2.4

2.8

3.2

Ammonium nitrate (34% N)

0.3

0.7

1.3

2

2.7

4

4.7

5.3

_____________________________________________________________________________________

 

 

Vegetables

Soils for growing vegetables should be limed to pH 6 to 6.5. Even the vegetables that have origins in the Western Hemisphere and which are tolerant of soil acidity will thrive well in limed soils. Recommendations for fertilization of vegetables may vary according to the type of soil--sandy, loamy, clayey, or organic mucks or peats. For example with tomato, fertilization ratios of N-P2O5-K2O range from 1-2-2 or 1-2-2 with sandy soils to 1-3-1 or 1-4-1 for loamy or heavier soils. Recommendations often are adjusted to allow for nitrogen that may be supplied in the first cropping season following the turning under of a leguminous green manure crop. If a leguminous green manure is turned in, no nitrogen may be applied in the first year. If a nonleguminous green manure is turned in, an additional 50 lb N/acre (1.2 lb/1,000 sq ft) over the recommended amount (Table 38) should be applied to get the maximum benefit in improvement in soil structure and to avoid nitrogen immobilization.

Crops that are productive with large or prolonged harvests will remove more nutrients than crops with small harvests and those that occupy land for a short period of time. Potato is an example of a productive crop with a large, one-time harvest. Tomato and cucumber are moderately productive crops usually managed with multiple harvests. Garden bean and pea are low-yielding crops. Radish is low-yielding and rapid-maturing, occupying the land for only a short period of time. In some cases, as with sweet corn, the yield of the harvested product may be low, but the total production of plant mass is great because of the large vegetative frame of the plants.

The recommendations in Table 38 are not rigid, but are guidelines to be considered when no other sources of information are available. Experience in production of the crops and history of fertilization of the land are among the additional items that vegetable growers should consider in crop fertilization.

Vegetable crops, being a diverse collection of species, differ widely in the amounts of nutrients that they absorb from the soil. Also, vegetable crops have meager root systems and are unable to exploit the soil fully for nutrients. To compensate for the fact that the roots do not come in contact with all of the fertilizer that is applied, amounts of nutrients applied in fertilization of these crops often are higher than the amounts of nutrients that the crops will remove. This practice applies particularly to the relatively low-yielding, low-vigor, small vegetable crops. Robust, high-yielding crops might remove about the same amount of nutrients as those applied in fertilizers. Therefore, although vegetable crops differ in the amounts of nutrients that they remove, the recommended amounts of fertilizers applied do not differ in proportion to the yields of the various vegetables (Table 38). Because of phosphorus fixation, application of phosphorus in excess of expected removal by a crop is a common practice with all crops. Fixation lowers the availability of fertilizer phosphorus in the soil sufficiently so that liberal applications of phosphorus are required to ensure adequate crop nutrition.

Table 38. Suggested amounts of fertilizer to apply to selected crops grown in medium-textured mineral soils in humid, temperate zones.

________________________________________________________________________

 

Kind of crop

Nutrients to apply
___________________________________________

...........lb/acre.....................|.......... lb/1,000 sq ft .........

High Productivity, > 200 cwt/acre

..N.....

..P205..

..K20..

...N...

..P205..

..K20...

Tubers:potato

200

200

200

5

5

5

Leaves: lettuce, cabbage

150

150

150

4

4

4

Stems: celery

150

150

150

4

4

4

Bulbs: onion

120

120

120

3

3

3

Roots: carrot, beet

100

150

150

2.5

4

4

Fruits: tomato

100

200

200

2.5

5

5

Moderate Productivity, 100-200 cwt/acre

Leaves: escarole (endive)

120

100

100

3

2.5

2.5

Flowers: broccoli, cauliflower

150

100

100

4

2.5

2.5

Fruits: cucumber, pepper, eggplant

100

100

150

2. 5

2.5

4

Fruits: melons

120

150

150

3

4

4

Low productivity <100 cwt/acre

Leaves: spinach

80

100

100

2

2.5

2.5

Fruits: sweet corn

120

120

120

3

3

3

Fruits: beans, peas

40

80

80

1

2

2

Roots: radish

60

80

80

1.5

2

2

Perennial Vegetables

Artichoke

80

160

80

2

4

4

Asparagus

100

100

100

2.5

2.5

2.5

Rhubarb

60

120

60

1.5

3

1.5


Productivity is based on the harvested product and not on the total dry matter that may be produced.

Example of fertilization: An application of 200 lb N, 200 lb P2O5, and 200 lb K20 per acre would require 2,000 lb
of 10-10-10; and an application of 5 lb N, 5 lb P2O5, and 5 lb K20 per 1,000 sq ft would require 50 lb of 10-10-10.

________________________________________________________________________


For crops in widely spaced rows (3 ft or more apart), the initial fertilizer might be banded along side the seeded or transplanted rows rather than worked into the bed. Banding places the nutrients in a concentrated zone in close proximity to the roots. Bands are placed usually about 2 inches below and 2 inches to the side of the row of crops (Figure 17). Banded applications of high analysis chemical fertilizers should not exceed 300 lb/acre (7.5 lb/1,000 sq ft) because of the possiblity of salt damage to the germinating seeds or to transplants. Higher applications should be broadcasted. Most of the applications recommended in Table 38 and in Table 39 will exceed this limit. Consequently, initial applications of fertilizer to most vegetable crops are by broadcasting and working in before planting. The best practice for vegetables is to apply half to two-thirds of the recommended fertilizer in the broadcasted application and to follow with the remainder of the fertilization in one or two sidedressed applications at 3 or 4 and at 6 or 8 weeks after planting.

Figure 17. Placement of fertilizer by (A) Broadcasting or (B) Banding. With either method of placement, fertilizer should be incorporated below the soil surface to ensure efficiency of fertilizer use and to restrict losses.

 

Organic fertilizers should be mixed into the soil about 2 weeks before planting. Generally applications of organic fertilizers to the land are relatively large. Applications of organic nitrogen fertilizers placed in close proximity to germinating seeds or young seedlings can promote rots or damping-off diseases that will kill the young plants. Ammonium released by the mineralization of organic matter, particularly with seed meals or blood meal, may injure seeds or young plants. The lead time of 2 weeks allows for decomposition of the organic matter and nitrification of ammonium to nitrate. If only organic phosphorus or potassium fertilizers, other than plant materials, are applied before planting, the lead time of 2 weeks is not needed. For the organic phosphorus and potassium fertilizers are so mild that toxic responses seldom occur.

In home gardens with previously cropped soils, growers may find it useful to use the following recommendations (Table 39).

 

Table 39. Practices for fertilizing a mixed home vegetable garden, based on experience obtained from observations of previous crops.

________________________________________________________________________

 

Yields & appearance of previous crop

..........................Amount of fertilizer to apply, lb/1,000 sq ft...........................

Worked into seedbed

Sidedressed after 4 weeks

N

P205

K20

N

P205

K20

Good, no deficiencies apparent

2.0

2.0

2.0

1.0

0

0

at 4 or 8 weeks

Poor, deficiencies apparent

3.0

3.0

3.0

1.0

1.0

1.0

at 4 or 8 weeks

or

2.0

2.0

2.0

1.0

1.0

1.0

at 4 or 8 weeks

Example of fertilization: To apply 2 lb N, 2lb P2O5, and 2 lb K2O per 1000 sq ft broadcase 20 lb of 10-10-10; to apply 1.0 lb N, 0 P2O5, and 0 K2O, sidedress 3 lb ammonium nitrate (34-0-0) divided equally on each side of about 33 ft of row with a spacing of 3 ft between rows in the garden.

_________________________________________________________________________________________

 

Flower Gardens

Annuals. Attention must be given to nutrition of seedlings before they are transplanted into gardens. Annuals that are started as seedlings in flats or other containers should be watered in these containers every 2 weeks with a solution of 15-30-15 or 20-20-20 (either fertilizer at 1 oz/gal) starting when the seedlings have developed true leaves or when the seedlings are pricked out of the flats and transplanted pots, cell packs, or other containers prior to placement in the garden. Seedlings that show signs of purpling of leaves while growing in the flats are phosphorus-deficient. The purpling is quite evident on the underside of the true leaves of seedlings. Chilling from an open window or in cold houses can cause symptoms of phosphorus deficiency to appear. In cold soils, phosphorus has low availability to plants, and seedlings have limited capacity to absorb the phosphorus that is in solution. Phosphorus deficiency lasting for more than a few days can stunt plants virtually beyond recovery. This deficiency if observed at its onset often can be cured by placing the flats in a warmer area or applying bottom heat. Fertilization is more effective in reversing the effects of phosphorus deficiency if the soil is warmed up first. Similarly, warming is more effective with phosphorus fertilization.

Garden soils should be limed to pH 6. About 2 to 3 lb each of N, P2O5, and K2O should be applied in the spring. In the garden, chemical fertilizers can be applied before or after seeding directly or transplanting into the garden. Fertilization is simpler and usually uniform if the fertilizers are mixed into the beds before planting. Organic fertilizers for nitrogen should be incorporated into the soil 2 weeks ahead of seeding or transplanting (see discussion for vegetables). This 2-week lead time will help deter damping off diseases and ammonium toxicity. Transplants can be watered in with a solution of 15-30-15, 20-20-20, or diammonium phosphate (18-46-0) (about 1 oz/gal of either fertilizer). Another application of fertilizer equal to or exceeding the initial one that was worked into the bed should be made at 4 to 6 weeks after planting. Chemical fertilizers used in this application can be surface applied. Raking of fertilizer into the top inch of soil is a good practice. If the fertilizers are not incorporated, use the higher range of the recommended amount (Table 40). Organic nitrogen fertilizers must be incorporated somewhat into the soil; otherwise, so much nitrogen will be lost to the atmosphere as to make their application useless. On the other hand, composts or manures with bedding of woodchips (or shavings) or sawdust can be applied as 1.5-inch thick mulches, and even though much nitrogen will be lost to the atmosphere, the total application from the mulch is sufficient to fertilize the garden.

Watering-in of chemical fertilizers immediately after their application helps with or without them raking in. A liberal irrigation after surface application of chemical fertilizers can substitute for mechanical incorporation. Little or no benefit of watering in of surface-applied organic fertilizers can be expected. Organic nitrogen fertilizers must be incorporated at least one-inch deep in the soil. At 8 to 10 weeks after planting of annual flowers, another application of fertilizer may be necessary. Judgement as to making this application assesses the appearance of the plants. Incorporation of this fertilizer into the ground may not be possible because of the chance of root damage and other disruption of the crop or a mulch, so a relatively heavy application may be necessary.

As soon as flower buds appear, some growers prefer to use a fertilizer with a lower nitrogen analysis than that used in the first or second fertilization. Too much nitrogen at this time may make the plants vegetative and suppress flowering. Most people, however, prefer to have flowers on nice green plants, so growers should not be too cautious on application of nitrogenous fertilizers. Fertilizers with high nitrogen analyses can be used just as well as low analyses ones, except that the high analysis ones should be used in lesser amounts after the flowers appear. It is doubtful that in the second or third application with dry fertilizers that phosphorus and potassium will move downward in the soil sufficiently to give a quick response of the plant to the fertilization. So, use of a nitrogen-only fertilizer (ammonium nitrate, urea) will suffice for these applications. Ammonium nitrate and urea are water-soluble and can be applied in liquids. The second and third application of fertilizers also can be made with a liquid fertilizer having a 1-1-1 ratio of mixed nutrients. The dissolved nutrients will move into the soil more quickly than those from the surface-applied dry fertilizers and may be effective in getting phosphorus and potassium to the roots. Improved growth of plants in late season, however, are normally in response to nitrogen fertilization. Costs of fertilization with the soluble nutrients of a complete fertilizer will be higher than the costs with dry materials. Fertilizers with only nitrogen in dry materials will cost less than application of the same amount of nitrogen in a multinutrient liquid fertilizer. Application of nitrogen from dry multinutrient fertilizers (such as 10-10-10) will not be a lot more expensive than using a single-nutrient fertilizer (such as ammonium nitrate, 34-0-0). If the gardener has the multinutrient fertilizer leftover from the first or second fertilization, that material can be used just as well as the single-nutrient, nitrogen-containing fertilizer. The phosphorus and potassium will remain in the soil and may benefit next year's garden. A recommended practice for fertilization of annual flower gardens or borders follows (Table 40). Downward adjustments in these amounts should be made for sparse planting and for species that are not heavy feeders of nitrogen. During periods of dry weather, fertilizers may be withheld to avoid wasting them and to avoid possibilities of overfertilization.

Table 40. Recommendation for fertilization of annual flowers.

Time

.........Nutrients per 1000 sq ft........

N

P205

K20

At or before planting1

1 to 2

2 to 3

2 to 3

After 4 to 6 weeks

2 to 3

2 to 3

2 to 3

After 8 to 10 weeks

2

0 to 2

0 to 2


1Transplants can be watered in with a starter fertilizer (1 oz 15-30-15, 20-20-20, or 18-46-0 per gallon).

Example of fertilization: For the application at or before planting use 20 or 40 lb of 10-10-10 per 1000 sq ft.
For the second application, use 20 or 30 lb of 10-10-10 per 1000 sq ft., and for the third application,
use 20 lb of 10-10-10.
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Perennials. Perennials including bulbs should be fertilized with surface applications of a fertilizer with a 1-1-1 ratio of nutrientsas soon as the ground thaws or as soon as the foliage begins to emerge in the spring. Caution should be taken not to apply fertilizer directly on the crowns or foliage of emerging plants. This application should be repeated every 4 to 6 weeks. In the fall, an application of 5-10-10, 0-20-20, or superphosphate also spread across the soil surface should be made. Instead of the chemical fertilizers, manures or composts can be applied as 1.5-inch deep mulches after the ground warms up in the spring. This application should fertilize the perennials for the remainder of the season. The application of these mulches should be avoided in the fall, for they may stimulate crown rots if applied early in the fall, and if applied late, nutrients, mostly nitrogen, may be leached or washed away. Specific recommendations for fertilization of perennial flowers are presented in Table 41.

 

Table 41. Recommendation for fertilization of perennial flowers.

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Time

...............Nutrients per 1000 sq ft..............

N

P205

K20

Spring

2 to 3

2 to 3

2 to 3

After 4 to 6 weeks

2 to 3

2 to 3

2 to 3

After 8 to 10 weeks

2

0 to 2

0 to 2

Fall

0

3

3

See Table 40 for examples of practices for fertilization. The fall application can be made with a
mixed fertilizer, such as 0-20-20.

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These recommended amounts of fertilization can be adjusted downward depending on the species, the weather, and appearance of the plants. Many growers may want to omit one of the midseason applications. With bulb crops, which die back in the summer, monthly applications at half the amount applied in the spring should be made until the foliage turns yellow.

Perennials grown in containers or held in containers before planting in the garden should be watered every 2 weeks with a solution (1 oz/gal) of 15-30-15,

20-20-20, or similar high-analysis, water-soluble fertilizer. In the garden soil, newly transplanted perennials should be watered in with a starter fertilizer of the high-analysis materials used for the container-grown plants or with diammonium phosphate (1 or 2 oz/gal). This application can be repeated if the plants show signs of nutrient deficiency or are not growing well during the season.

Bonemeal can be mixed in the soil or placed at the bottom of the planting hole with bulbs. Phosphorus from the bonemeal will help in root development which is necessary for hardiness of the bulbs in the ground. If bonemeal is impractical or too expensive to use, a fertilizer with a ratio of 1-2-2 (5-10-10 at 3 lb/100 sq ft) can be applied over the soil surface. Superphosphate (0-20-0 or 0-46-0) can be mixed at the bottom of the planting hole, but granules of the superphosphate should be kept about 0.5 inch (1 cm) from the bulbs. Avoid fall applications of manures or composts over newly planted or established bulbs, as these applications may cause bulbs to rot. Use spring or summer applications with caution. Mulches of bark or woodchips are better over bulbs than manures or composts.

Roses require regular applications of fertilizer for optimum growth and appearance. Newly planted roses should be in a bed that is well fertilized with phosphorus to stimulate root growth. Before planting, a phosphorus fertilizer should be incorporated into the top 6 inches of the bed. The application should provide 0.5 lb P2O5/100 sq ft. An application of about 3 lb bonemeal or ordinary superphosphate (0-20-0) or about 1.5 lb triple superphosphate (0-46-0) per 100 sq ft will meet this requirement. If these fertilizers are worked deeper than 6 inches into the soil, consider using twice these amounts. The regular fertilization program for roses should begin 3 or 4 weeks after planting and should follow the guidelines in Table 42 with the probability of including a third summer fertilization at 12 weeks into the season.

Herbs

Herbs are any plants, woody or herbaceous, of which the leaves, stems, bark, roots, flowers, fruits, seeds, or other parts are used for fragrance, flavor, medicine, dye, or cosmetic use. Spices are herbs used for fragrance and flavor. Fertilization of garden herbs is like that of flowers or vegetables. Therefore, herbs should be fertilized as flowers (Table 40) if they are part of the flower garden and as vegetables if they are part of the vegetable garden (Table 38). Perennial herbs should be treated as perennial flowers (Table 41). Lush foliage on herbs may result from liberal fertilization with nitrogen and may have lesser fragrance and flavor than foliage of herbs fertilized less generously.

Lawns

Although broadleaf species, such as white clover (Trifolium repens), may be desired or tolerated, grasses are the most common species in lawns. Maintenance of good quality turf in the lawn usually requires a vigorous program of fertilization. Fertilization of lawns with nitrogen fertilizers promotes the domination of grasses by increasing the competitive capacity of grasses with respect to broadleafed plants and weeds. The purity of stand with respect to turfgrasses is increased by nitrogen fertilization.

Lawn grasses are classified broadly into cool-season and warm-season species. Each group is fertilized differently. Cool-season grasses grow actively in the spring and fall and slowly in the summer. Cool-season grasses may remain green without summer fertilization if they are watered adequately. Warm-season grasses grow vigorously in the summer and become dormant, turning brown, in cold weather. Warm-season species require fertilization during the summer to maintain their growth. They are fertilized more lightly the fall than the cool-season species.

Warm-season grasses are grown in cool climates but often are less winter hardy than cool-season species. Bluegrass (Poa pratensis), fescue (Festuca rubra), ryegrass (Lolium sp.), and bentgrass (Agrostis sp.) are among the common cool-season species. Bermudagrass (Cynodon dactylon), St. Augustine grass (Stenotaphrum secundatum), and zoysia (Zoisia sp.) are commonly grown warm-season species.

An ideal soil for lawn grasses is a rich loam at least 6 inches deep, but with proper fertilization, grasses can be grown on almost any soil. No one program for fertilization can be developed to suit all conditions. The needs for fertilizer will vary according to the species and varieties being grown, the conditions of the soil, the climate, the quality of turf desired, and the kind of fertilizer applied.

The upper 3 inches of soil should be limed to pH 6 before the lawn is seeded. Most fertilizers used on turf are formulated with ammonium salts or urea, which will cause acidification of the soil. The soil should be tested every 3 years to ensure that the pH has not fallen below an acceptable range (minimum pH 5.5 to 6).

A grower has many options in fertilization of turfgrasses. The general principles in fertilization to maintain a green lawn are to supply 4 to 5 lb nitrogen per 1,000 sq ft divided in two or more applications over the season. With split applications in a season, the first and last should be made with complete fertilizers, that is, those containing nitrogen, phosphorus, and potassium. The middle application in summer can be made with a complete fertilizer or with one supplying only nitrogen.

Over the entire season, nitrogen is provided at four times the amount of phosphorus (P2O5) and at two times the amount of potassium (K2O). Either a single fertilizer with nutrient ratio of 4-1-2 applied three times during the growing season or a seasonal program that provides nutrients in this ratio would be appropriate. The recommendations in Table 42 provide a seasonal program that supplies nutrients at a 4-1-2 ratio, using a complete fertilizer for the first and last application and a nitrogen-only fertilizer for the middle application.

Cool season grasses should be fertilized in the spring and in the late summer or fall and occasionally in the summer depending on the weather. The summer application for cool-season grasses is a lighter application of nitrogen than that for warm-season grasses. Sometimes cool-season grasses will stay green without nitrogen fertilization in the summer if they are watered well. Nitrogen fertilization may be needed to maintain their green color if considerable growth is made during the summer, if considerable leaching occurs from rainfall or irrigation, or if the clippings are removed during mowing.

 

Table 42. Recommendations for a seasonal program for fertilization of lawns.

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Time of season

...............................Type of grass.............................................

.........Warm-season............

..........Cool-season...........

N

P2O5

K2O

N

P2O5

K20

Spring

2

0.8

1.5

2

0.8

1.5

Summer

2

0

0

1

0

0

Fall

1

0.5

1

2

0.5

1

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Warm-season grasses should be fertilized in the spring, summer, and fall. The fall application of the warm-season grasses should be lighter in nitrogen than the spring and summer applications. Fall fertilization may stimulate the growth of winter weeds in the dormant turf. Flushes of succulent growth promoted by fall application of nitrogen may weaken the plant to cold injury. Warm-season grasses as stated earlier are less winter hardy than cool-season grasses.

The spring application for either type of grass should be when the grass starts to grow. Grass starts to grow when the soil warms to about 40o F (4o C). The first sign of green on the lawn indicates the need of the spring application of fertilizer. This fertilization can be made with a complete fertilizer, but the nitrogen component should be water soluble for best results. The common commercial fertilizers for general-purpose use contain water-soluble nitrogen sources. Fertilization also can be made with individual fertilizers, for example, urea, ammonium nitrate, superphosphate, diammonium phosphate, and potassium chloride. The nitrogen fertilization should be with water-soluble nitrogen (4.4 lb urea or 6 lb ammonium nitrate per 1,000 sq ft) applied just before a rain or irrigation. Rain or irrigation wash the nitrogen off the foliage and into the soil, lessing the chance of foliar burn (desiccation) and increasing the recovery of the fertilizer by the plants. Results from this fertilization, shown by greening of the grass, should be evident in a week. A complete fertilization for spring may include superphosphate (1.75 lb/ 1,000 sq ft) or diammonium phosphate (1.5 lb/1,000 sq ft) and potassium chloride (2.5 lb/1,000 sq ft).

Fertilizers with slow-release nitrogen compounds (urea formaldehyde, sulfur-coated urea, isobutylidene diurea, feather meal, digested sewage sludge) also may be used in the spring application. Growers should consider increasing the nitrogen application to 3 lb/1,000 sq ft if slow-release fertilizers are used in the spring. Remember that the recommended application with water-soluble fertilizers is 2 lb N/1,000 sq. ft. Several weeks may pass before results of fertilization with slow-release materials are evident.

The summer fertilizations of cool-season or warm-season grasses should be with one of the slow-release nitrogen fertilizers. Slow-release fertilizers will have a delay of at least one week before enough nitrogen is released to be of benefit to the grasses, and then it may be another week before the benefit is noticeable. If the sod is showing symptoms nitrogen deficiency in the summer, growers may want to consider using a fertilizer formulated with 50% slow-release chemicals and 50% water-soluble chemicals or to use one of the slow-release formulations with a relatively rapid dissolution rate. Also, slow-release fertilizers with small granules will release nitrogen faster than ones with large granules.

The fall application should be after August in most climates but early enough that the sod will benefit from and hold the nutrients. The fall-applied fertilizer should be complete with nitrogen, phosphorus, and potassium. The phosphorus and potassium in a complete fertilizer help to minimize winter injury. The nitrogen in the fall-applied fertilizer should be water-soluble, but this requirement is not inflexible. Slow-release nitrogen fertilizers may be used, but the quantity of application may need to be increased or one of the more labile forms may be used. Stabile slow-release fertilizers may not release enough nutrients in time to benefit the grass in the fall and may carry over to the next season. Weathering of the fertilizer may cause some losses by leaching. The grower would have to be aware of the possibility of carry-over of nitrogen and make the proper downward adjustment in fertilization when with the spring application in the next season. The color of the grass in the spring will guide the grower as the whether or not an adjustment in fertilization is needed in the spring. A grower may find that the carry-over is uneven across the lawn and may opt for a uniform application of fertilizer at the recommended rate (Table 42), ignoring the possibility of residual nitrogen from the fall fertilization. The uniform spring fertilization will promote recovery of an even stand and appearance of the grass.

Often the fall application is made after the last mowing and when the grass has stopped growing. However, fall applications of soluble fertilizers made after the grass has slowed growth too much or has become dormant may result in waste of fertilizer and substantial leaching losses of nitrogen, as well as injure the stand.

Many times, lawns are maintained throughout the season with one of the fertilizers formulated especially for turf. Many different types of these fertilizers are available. The label on the package will tell the grade of the fertilizer, for example, 22-4-8. In addition to the total nitrogen, the percent water-insoluble nitrogen will be indicated. For example, a fertilizer may be 22% total nitrogen with half or 11% being water-insoluble nitrogen. The water-insoluble nitrogen will be from one of the slow-release nitrogen carriers (ureaform, sulfur-coated urea, or others). By difference, 11% of the nitrogen is water soluble. The carriers of the water-soluble fraction may be urea, ammonium nitrate, or other nitrogen salts. The application of the specialty turf fertilizers should be made according to the nitrogen content of the fertilizers. With the 22% nitrogen fertilizer mentioned here, 9.1 lb/1,000 sq ft should be applied for the spring application, with 4.6 or 9.1 lb/1,000 sq ft for the summer application and fall application according to the type of grass (Table 42).

The slow-release and specialty fertilizers are much more expensive than those made from water-soluble nitrogen carriers. A program of fertilization can be developed using only the water-soluble materials. This practice is simpler and often more convenient than one that uses a different fertilizer at each time that the grass is fertilized during the season. (Note that the program discussed above recommends that the summer application be with slow-release materials.) If this program using only water-soluble fertilizers is adopted, fertilization will need to be more frequent than three times per season. Four or five applications of nitrogen at 1 to 1.25 lb/1,000 sq ft every 4 to 6 weeks usually maintain a good green appearance of grass. Urea is the most widely available fertilizer for use any time during the growing season. With this practice, the first and last applications should provide the phosphorus and potassium recommended (Table 42).

Commonly, on old, established lawns, only nitrogen-containing fertilizers are used to maintain the turf. The frequency of fertilization depends in large part on the grower's preference on appearance of the lawn and on how the mowing of the lawn is managed. Maintainence of green grass in established lawns requires frequent applications of nitrogenous fertilizers, such as 1 to 1.25 lb N/1,000 sq feet every 4 to 6 weeks as mentioned in the preceding paragraph. If grass clippings are removed at mowing, more fertilization may be required than if they are left on the lawn.

Ground Covers

Ground covers are a diverse group of plants. They may be perennials or self-seeding annuals, broad-leafed or needle-leafed, evergreen or deciduous, herbaceous or woody, and have differing habits (forms, sizes) of growth. The functions of ground covers vary widely. They may be grown to protect the soil or for their ornamental value independent of any other planting. They may grown to complement other plantings. The kind of ground covers and their function affect how they should be fertilized.

To establish ground covers, they should be planted in beds in which a fertilizer such as a 5-10-10 has been surface applied or mixed in the soil at 20 to 30 lb/1000 sq ft (2 to 3 lb/100 sq ft). If a mulch is applied, the fertilizer should be applied before the mulch. Application of fertilizers on the mulch will accelerate the decay of the mulch, which may or may not be a desirable action. Decay of the mulch will cause loss of its function in weed control and moisture conservation but may allow for release of nutrients to nourish the ground cover. Mulches are expensive and time-consuming to apply, and generally one does not want to promote degradation of the mulch. Also application of fertilizers to the top of mulches is less efficient in nutrient recovery by the grown covers than direct application of the fertilizers to the soil. Eventually, the ground covers will dominate the surface of the ground, and the mulch will be obscured. Thereafter, an annual surface application of 5-10-10 or 10-10-10 at 20 to 30 lb/1,000 sq ft should maintain nutrition to the ground covers.

If ground covers are grown essentially as bedding plants, they should be fertilized as annual flowers (Table 40). If they are grown as independent perennial beds, they should be fertilized as perennial flowers (Table 41). Ground covers grown complementally with shrubs or trees will receive adequate nutrition if the shrubs or trees are fertilized. If the shrubs or trees are not being fertilized, the ground covers may need fertilization.

Appearance of the covers should be the criterion as to whether or not to fertilize. If the ground covers show symptoms of nutrient stress, they should be fertilized with a complete fertilizer such as a 5-10-10 at 2 to 3 lb/100 sq ft in the fall and early spring until good growth and appearance of the covers are achieved. Two applications in the spring and one in the fall may be needed. Thereafter, annual applications of this amount in the spring or fall will be sufficient.

Shrubs and Trees

Shrubs

One must start considering a fertilization program for shrubs as soon as they are planted. Other than in the late spring or late fall when approaching hot or cold weather will place newly planted shrubs under stress, shrubs can be planted from container-grown stock or transplanted at any time that the soil is workable. The hole in which the shrub is to be planted should be as deep and twice the diameter of the root ball. Although not mandatory, mixing some peatmoss (about 1:3 peat:soil by volume) with the soil to fill around the plant aids later in fertilization of the shrub. A minor problem with using the peat is that its decay in later years may require some backfilling. After the soil has firmed around the roots following several waterings, rain, and time, fertilizer may be applied (Table 43). If the grower does not want to have to return to fertilize the shrubs after planting, the fertilizer may be mixed into the soil used to backfill the hole, but care should be taken to ensure that the roots of the shrub do not come in direct contact with any chemical fertilizers or organic nitrogen fertilizers. Peatmoss or other organic matter in the backfilling soil facilitates the movement of surface applied nutrients into the soil around the roots if fertilizers are applied soon or a few weeks after planting. Mobility of phosphorus in particular is much improved in soils amended organic matter relative to its mobility in unamended soils.

 

Table 43. Fertilization of newly planted shrubs.

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Size of container or approximate size of root ball

Amount of fertilizer to applyz

_________|............Nutrients delivered, oz/plant................

oz/plant

N

P2O5

K20

1 gallon

2

0.2

0.2

0.2

5 gallon

4

0.4

0.4

0.4


z 10-10-10 applied at planting or as soon as the soil has firmed around the shrubs after planting.

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Nitrogen is usually the nutrient that limits the growth and appearance of newly planted shrubs. If at 4 to 8 weeks after planting, the shrub shows foliar signs of nitrogen deficiency (yellowing of old or all leaves), 4 oz to l lb of a complete low analysis fertilizer (5-10-10 or 10-10-10) or 1 to 4 oz of ammonium nitrate (34% N) or urea (46% N) can be applied and watered or raked in starting out about 6 inches from the stem of the shrub. Regulate the amount of fertilization in direct proportion to the size of the shrub and the size of the hole in which the shrub was planted.

Fertilization of established shrubs depends on the location and conditions under which they are grown. Shrubs that are in or near lawns or gardens or mulched deeply with organic matter may not need supplemental fertilization. Young shrubs that are growing rapidly in unmulched soil that does not receive indirect fertilization from lawns or gardens should be fertilized annually until the shrubs reach their mature size (Table 45).

Table 44. Annual fertilization of shrubs following the year of planting.

________________________________________________________________________

Location or condition

Amount of fertilizer to apply

lb/100 sq ft areaz

In fertilized areas (lawns, gardens)

0

Heavily mulched (> in deep), slow growing, or both

0

Unfertilized, unmulched, rapid growing shrubs

0.2 lb N - 0.2 lb P205 - 0.2 lb K20 (2 lb 10-10-10)


zThe area that is fertilized should extend half of the height of the shrub beyond the dripline of the shrub.

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Trees

Newly planted ornamental or shade trees should be fertilized in the same manner as newly planted shrubs (Table 44 and 45). Nitrogen fertilization is needed after planting to promote rapid growth and to allow the trees to reach landscape size rapidly. Other than with the fertilizer applied near or in the planting hole at planting or soon afterward (Table 44), nitrogen is the only nutrient likely to reach tree roots. In the first year at about 4 to 8 weeks after planting, 2 oz of nitrogen (6 oz ammonium nitrate or 4 oz urea) should be applied. In the second year after planting, 4 oz of nitrogen (12 oz ammonium nitrate or 8 oz urea) should be applied. In both years, fertilization should begin 6 to 12 inches from the trunk and extend outwardly in a circle to 5 feet from the tree. As the tree grows, the amount of nitrogen can be increased incrementally to 2 to 4 lb per 1,000 sq ft covering an area from 1 foot from the trunk outward to a distance half of the height of the tree (Figure 18). The fertilizer that is applied can be an all nitrogen one (ammonium nitrate, 34% N; urea, 46% N) or a mixed one (5-10-10, 10-10-10, ammonium phosphate, calcium nitrate, and so on) (Table 47). The trees are likely to benefit only from the nitrogen, so purchase and use of the multinutrient fertilizers should be only as a matter of convenience. Rates of fertilizer application are based on the nitrogen concentrations in the fertilizers. Unless they are shaded out, undergrowth and lawns will benefit from the other nutrients.

Figure 18. Illustration for fertilizer placement around a tree. Start fertilization at 12 inches from the trunk and continue application until reaching a distance equal to half the height of the tree, all around the tree.

Recommendations for fertilization of trees sometimes are based on the diameter or caliper of the tree trunk. Where to measure the caliper is a matter of judgement, but location on the trunk will range from a foot above the ground to breast-height (about 4.5 ft) above the ground. For each inch of caliper, apply 2 to 4 oz of nitrogen under the tree until the tree reaches landscape size.

Once trees have reached a desired size for the landscape or an apparently mature size, fertilization is not needed. Further fertilization may be undesirable in that it promotes growth of tree beyond acceptable size and increases the amount of foliage above beneficial levels (leaves shade one another or transpire and dry the soil).

Table 45. Recommendations for fertilization of trees in a landscape.

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Stage

Amount of fertilizer to apply

At planting

0.4 oz N per tree

First year, 4 to 8 weeks after planting

2 oz N per tree

Second year

4 oz lb N per tree

Following years to maturity

2 to 4 lb N/1000 sq ft around tree

In fertilized areas (near lawns, gardens)

0

Mature trees

0

_________________________________________________________________

 

If trees are grown in fertilized lawns or other fertilized areas, no fertilizer needs to be applied. If the lawns are underfertilized, the trees, particularly young ones, will not get adequate nitrogen nutrition. Nitrogen deficiency symptoms that appear on undernourised trees can be confirmed by examining the grass and weeds in the lawn or area surrounding the trees. If the surrounding vegetation shows signs of nitrogen deficiency, the grower can be certain that the symptoms on the trees are also those of nitrogen deficiency. The grower should choose a site at least half of the height of the tree away from the base of the tree as the area in which to make the assessment. Vegetation directly under the tree may be suffering from the superior competition of the tree for light, water, and nutrients.

Table 46. Amount of several fertilizers needed to provide one ounce of nitrogen.

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Fertilizer

Ounces of fertilizer per ounce of nitrogen

5-10-10

20

10-10-10

10

Ammonium nitrate (34%N)

3.0

Urea (46% N)

2.2

Diammonium phosphate (18% N)

5.6

Calcium nitrate (15% N)

6.7

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