Fertilizing Apple Trees

Table of Contents

1. General Soil Fertility
2. pH Requirements
3. Leaf Analysis For Apple Trees
4. Fertilizing Non-Bearing Apple Trees
5. Fertilizing Bearing Apple Trees
6. Micronutrients for Apple Trees
7. Related Links

General Soil Fertility

Soil preparation and soil testing before planting trees is important. To ensure long term productivity of this perennial crop, prepare the soil through tillage and additions of organic matter well in advance of planting. Prior to planting, ensure nutrient levels and pH are adequate. Test the soil and apply fertilizer and lime if necessary. Phosphorus, potassium and lime do not move readily through the soil and pre-plant applications are the most effective. See OMAFRA Publication 360, Fruit Production Recommendations for more information on apple production.

| Top of Page |

Manure for Orchards

Animal manure contains varying levels of nutrients and organic matter. The disadvantage of adding manure to orchards is that the nitrogen is released over a prolonged period of time. This slow release means this perennial crop continues to receive nitrogen throughout the year, resulting in poor fruit colour, excessive terminal growth and delayed hardening of the woody tissue. This makes trees more susceptible to winter injury. The practice of putting manure around newly planted trees is not recommended because of potential winter injury problems. If manure is used, it should be broadcast at moderate rates and worked into the soil in late fall or early spring before planting.

No more than 7 t/ha of poultry manure, 40 t/ha of cattle or 35 t/ha hog should be applied. Since manure is extremely variable in nutrient content, make sure you analyze it for nutrient content before application. When manure is used, reduce the rate of fertilizer.

| Top of Page |

pH Requirements

The pH of a soil is a measure of its acidity. If the pH is not at an acceptable level, nutrient uptake and crop performance can be hindered. To determine pH, take a soil sample. Always take a soil sample before establishing a new planting. If lime is required, incorporate it during soil preparation. In established orchards, a soil sample in the tree row is recommended every 3 years to be sure the pH is at a satisfactory level. If pH is low (acidic), lime can be applied to the sod cover in the fall, or before cultivation in the spring. The results will not be immediately evident because lime moves slowly into the soil. The target pH before establishing a new orchard is 6.5 on sandy soils and 6.0 on clay soils. If the pH in established orchards is above 5.6, lime is not needed. In established orchards, when the pH on clay loam soils drops below 5.1, and on sandy soils below 5.6, apply lime. This will raise the soil pH (reduce the acidity), and also supply calcium. Use dolomitic lime (high in magnesium) on soils low in magnesium. Rates of application will vary with soil type and initial pH. The buffer pH indicates the rate of lime to apply.

| Top of Page |

Leaf Analysis

In established plantings, leaf analysis is the best method of determining nutrient needs. The nutrient levels in these plant tissues most accurately reflect the uptake of nutrients by the tree. Soil analysis is used in conjunction with leaf analysis to determine the nutrient status of the soil and to monitor soil acidity. A combination of both analyses best evaluates fertilizer and lime needs. Nutrient uptake is affected by many orchard conditions. Consequently, each year the nutrient levels vary slightly depending upon the season. In order to obtain optimum growth and fruit quality, adequate levels of all nutrients must be present in the leaves and the relative amounts must be balanced. Even with optimum levels of nitrogen and potassium, poor growth can be attributed to low levels of magnesium, boron, zinc or other micronutrients, which will be reflected in the leaf analysis. Further information is available in OMAFRA Factsheet Leaf Analyses for Fruit Crop Nutrition, Order No. 91-012.

| Top of Page |

Fertilizing Non-Bearing Apple Trees

Prior to planting is the only time elements such as phosphorus, boron and lime can be effectively worked into the soil. Nutrient levels in the topsoil considered adequate for orchard establishment are 12-20 ppm phosphorus, 120- 150 ppm potassium, 100-250 ppm magnesium, and 1000-5000 ppm calcium. During the early years, before new trees bear their first crop, an annual application in early spring of nitrogen and potash is usually required. If the soil has been prepared properly, including deep cultivation and addition of organic matter, there should be an adequate supply of other nutrients to sustain the tree in the juvenile years. On coarse-textured, infertile soils, the use of a starter solution at planting time (e.g., 10-52-10 or 20-20-20) may give the trees a needed boost. High nitrogen levels can result in excessive growth and incomplete tree hardening. The use of cover crops to check late season growth in cultivated orchards is strongly recommended, especially in new plantings. Cover crops such as Italian rye grass, sown about July 1, take up much of the available nitrogen in the soil - checking tree growth. On young trees, broadcast the fertilizer under the spread of the branches at least 15 cm from the trunk, since injury can result if placed too close.

| Top of Page |

Fertilizing Bearing Apple Trees

Most bearing orchards require annual applications of both nitrogen (N) and potassium (K) fertilizer. These 2 elements significantly affect growth and productivity. Do not apply excessive amounts of nitrogen. Late or excessive applications may result in poor fruit colour and quality. Also, available nitrogen late in the season encourages the tree to grow instead of hardening off, increasing the possibility of winter injury.Using cover crops in cultivated orchards helps to lower the nitrogen level in the latter part of the season. Cover crops such as Italian rye grass, sown about July 1, take up much of the available nitrogen in the soil, thus checking tree growth. In herbicide-treated strips under trees, weed growth late in the season takes up extra nitrogen, helping to harden off trees and improve fruit quality.

| Top of Page |

Nitrogen (N)

Nitrogen is necessary for many tree functions including growth, fruit bud formation, fruit set and fruit size. Cultivars differ in their nitrogen requirements. A cultivar grown for processing could receive more nitrogen than one for the fresh market. In some situations, if fruit tends to be small, more nitrogen may be needed. Rootstocks, spacing and pruning also influence application rates. If pruning is to be severe, cut nitrogen rates back or eliminate it for a year. Tree growth, foliage colour, fruit quality including colour and storability, nutrient balance in leaves and soil, are also important considerations. Because of the complexity of nitrogen interactions with quality and production, the best guide for nitrogen rates is leaf analysis. Do not apply urea (46-0-0) to sod orchards since some of the nitrogen may be lost by volatilization. There are several forms of nitrogen available, but ammonium nitrate (34-0-0) or calcium ammonium nitrate (27-0-0) is the most economical form of nitrogen to use. If you are using blended fertilizers for your orchard, request ammonium nitrate as the N source.

Nitrogen Rates

Given the variety of orchards systems, rootstocks, cultivars, and soil types, it is difficult to report the exact amount of nitrogen to apply. Research is under way to better evaluate the nitrogen needs of higher density supported planting systems. Until that research is completed be careful with nitrogen applications. Rely on leaf analysis to evaluate the nitrogen needs of your specific plantings. When the tree canopy has covered the space available, nitrogen fertilizer requirements will level out and will not increase indefinitely with tree age. Orchards grown under clean cultivation require about ½ the nitrogen required by orchards grown in sod. Again leaf analysis is the most reliable guide. For all apple cultivars, do not exceed the maximum rates of 200 kg actual N/ha per year, even in the case of a severe deficiency. The table below provides approximate N application rates per tree at various tree density and tree ages, growing in sod.

Reduce nitrogen rate by half if orchard is cultivated without sod between tree rows. Do not exceed 200 kg of actual nitrogen/hectare/year regardless of the number of trees/hectare. These are approximate values. The exact amount of nitrogen to apply is a function of soil nitrogen level, cultivar, rootstock, soil moisture, etc. The best way to determine nitrogen requirements is by taking leaf analysis regularly.

Nitrogen Placement and Timing

Apply nitrogen fertilizer in early April. In cultivated orchards broadcast nitrogen under the tree canopy. In sod orchards place the nitrogen in a band under the drip line, or in the herbicide strip.

Foliar Application of Nitrogen

Foliar applications of urea (46% nitrogen) have been used successfully on apples, when weather or crop conditions resulted in a need for additional nitrogen at a critical time. Late applications may adversely affect fruit quality. On apples, use no more than 2.7 kg N/1000 L water (6 kg urea) and apply at least 2000 L/ha starting 7-10 days after petal fall, and spacing the sprays about 10 days apart. Do not apply more than 3 times. Do not apply later than the end of July, or fruit quality and winter survival of the tree could be adversely affected. Do not rely on urea sprays to completely substitute for soil applications if nitrogen is required.

| Top of Page |

Phosphorus (P)

Phosphorus is not required in large amounts by apple trees. With few exceptions the level of phosphorus in Ontario soils is adequate at present without additional being required. Phosphorus does have a place for sod or cover crop maintenance. A soil test is the best way to determine if there is a need to apply this nutrient to the sod cover. In the absence of a soil test, a complete fertilizer (100 kg/ha 10-20-20) could be broadcast and incorporated before seeding a cover crop in an orchard. Phosphorus should also be applied before planting an orchard when it can be thoroughly incorporated in the soil if a soil test indicates a need. Phosphorus soil test values between 12-20 ppm are considered adequate for tree fruit establishment and production.

| Top of Page |

Potassium (K)

Potassium is important for fruit colour, winter hardiness, tree growth and disease resistance. An excess amount of potassium can lead to deficiency of magnesium (Mg), so take care when deciding upon potassium rates. Potassium soil test values between 120-150 ppm are considered adequate when planting tree fruits. Muriate of potash (0-0-60) is the most common form of potassium. If leaf analysis data is not availalable, use approximate rates as noted in the table below. Apply no more than 3 kg of K2O (5 kg muriate of potash) per mature standard apple tree in a year, regardless of how severe the deficiency. When fertilizing trees of dwarfing rootstock, please refer to the table below for approximate rates of muriate of potash to apply. When the tree canopy has covered the space available, potassium fertilizer requirements will level out and will not increase indefinitely with tree age. Again leaf analysis is the most reliable guide.

Placement and Timing

In early spring, apply potassium separately or combined with nitrogen. Some orchardists make fall applications because of time constraints in the spring. However, some potassium may be lost by leaching over winter. For this reason, apply in spring if possible. In sod orchards, apply potash in a band around the dripline or in the herbicide strip.

| Top of Page |

Magnesium (Mg)

Magnesium deficiency is becoming more evident in orchards, particularly when high rates of potash are used. Magnesium deficiency can lead to premature drop of fruit at harvest, especially with McIntosh. Magnesium deficient trees have older leaves that are pale in colour, as magnesium is a part of the chlorophyll molecule. Leaf analysis is the best way to evaluate Mg needs. Foliar sprays of magnesium are effective in correcting this deficiency for the current year only. The table below shows rates of Mg foliar applications. For more permanent correction, soil applications of Mg are required. Magnesium soil test values between 100-250 ppm are considered adequate when planting tree fruits. Fruit or foliage injury is possible from a mixture of pesticides with magnesium sulfate; therefore, apply magnesium sulfate separately or try it on a few trees first. Check manufacturer's label regarding mixing magnesium chelates with pesticides.

For long-term corrections, soil applications of Mg can be made, but the response is not usually immediate. On some soil types, a single early spring application of soil applied Mg has not worked well. A second or third application the following spring may be required before the Mg level in the tree improves. To be sure that fruit drop is not a problem during this waiting period, apply foliar sprays for the first 2 years, in addition to soil applications. For soil corrections on acidic soils, use dolomitic limestone to supply magnesium and raise the soil pH. Where lime is not required, apply 5-7 kg/mature standard tree, and 3-4 kg/mature dwarf tree of sulphate of potash magnesia. This is a granular fertilizer containing approximately 21% potash and 11% magnesium. This material is applied in early spring in a band under the tree dripline. It contains potassium (K) and the rate of application depends on potash needs. No further potash (e.g. 0-0-60) is needed, but apply nitrogen at recommended rates. Other sources of Mg may also work well as a soil application. If Mg is being blended with the fertilizer, apply at least 80 kg of available Mg per hectare when the fertilizer is spread.

| Top of Page |

Calcium (Ca)

Lack of calcium is associated with fruit problems in apple. In Ontario, bitter pit of apple is the most common problem associated with calcium. Foliar applications of calcium (Ca) to apples reduces the incidence of bitter pit and cork spot. Where these disorders have been a problem in the past, 4 foliar sprays, applied 2 weeks apart, beginning in mid-July, works well. Consult the table below, Calcium Foliar Sprays, for more details. Where a greater amount of total calcium is required, additional applications can be made by beginning earlier (mid-June) or by continuing until harvest.

Timing: 4 sprays spaced 2 weeks apart beginning in mid-July. Additinal sprays can be applied up to harvest

*When using calcium chloride, mix the required calcium in a pail of water first, to be sure that
all the product is dissolved before adding the slurry to the spray tank.

Calcium has been shown to advance fruit maturity, and adjustments in harvest timing may be required as a result of calcium foliar sprays. Some formulations of calcium chloride (CaCl2) have resulted in poor fruit finish if applied too close to harvest. Calcium sprays must contact the fruit for uptake to be effective, therefore water volumes capable of wetting the entire tree are required. The more calcium that can be applied, the better the control - but there is a concentration at which calcium can cause foliar burning. Do not concentrate CaCl2 (77% flakes) beyond 5 kg/1000 L of water at the mid-July timing and no more than 7 kg/1000 L for the applications at or beyond mid- August. Do not apply Ca formulations containing nitrogen after the end of July, or fruit quality and storability may suffer. For all the formulations, be sure to consult label directions for concentrations to use and for compatibility with pesticides. The product used is not as important as the total amount of actual (elemental) calcium applied. For example, calcium chloride (77% flakes) contains 28% actual calcium. For acceptable results, up to 12 kg/ha of actual Ca is often required in a total of 4, or more, sprays. Ca sprays may cause foliage and/or fruit injury if applied when low temperature and wet weather delay drying of the spray. Injury can also occur if calcium is applied in hot (over 25oC) or humid weather. Recent studies with calcium sprays on McIntosh have failed to show an advantage in fruit firmness and keeping quality when fruit was stored in a regular controlled atmosphere storage for 5 1/2 months. Applications of Ca should be limited to fruit that has a known deficiency and/or is prone to bitterpit or cork spot. For more information on calcium disorders, consult OMAFRA Factsheet Bitter Pit Control in Apples, Order No. 00-009.

| Top of Page |

Micronutrients for Apples

Deficiencies of micronutrients or trace elements are not widespread in Ontario apple plantings. Boron deficiency is perhaps the most common. Deficiencies of zinc, manganese, and iron may show up occasionally, particularly in alkaline soils. The desirable range for micronutrients is quite narrow. More damage is possible with excesses than with deficiencies. For this reason, do not apply micronutrients to apples except when deficiency is confirmed by leaf analysis or visible symptoms. Only the nutrient that is deficient should be applied in sufficient quantities to correct the problem.

| Top of Page |

Boron (B)

Boron deficiency occurs mainly on alkaline soils or on sandy knolls. Apples are the most sensitive of the fruit crops to boron deficiency. Symptoms include internal breakdown of highly coloured fruit that drops prematurely. A boron concentration in apple leaf tissue in mid- July of less than 20 ppm is considered deficient. Apply foliar sprays of soluble boron fertilizers such as "Solubor" at rates supplying 0.2 kg of available boron/1000 L water (1.0 kg Solubor/1000 L). Two applications 10-14 days apart starting in early June is usually adequate. When there is a boron deficiency, spray at least 2000 L/ha at each application. Other formulations of boron are available. Consult manufacturer's label for rates and timing. Boron excess may cause yellowing of leaf edges and midrib, reduced yields and a shortened storage life.

| Top of Page |

Manganese (Mn)

Manganese deficiency occurs occasionally in fruit growing areas of Ontario. Its occurrence is closely related to weather conditions, particularly rainfall and soil moisture, as well as soil pH. It is most prevalent in wet seasons or with high soil pH (alkaline conditions). In mild cases of deficiency, there is a yellowing of the interveinal leaf areas of young leaves near the shoot-tip. Normally, this is not serious. Leaf manganese concentrations below 20 ppm in mid-July are considered deficient. Fruit size, yield, and quality appear to be unaffected. If the condition is severe, spray manganese sulfate at the rate of 1.3 kg of available Mn/1000 L water (5 kg manganese sulfate) at 2000 L/ha. Manganese chelates are also effective in correcting manganese deficiency. Consult manufacturer's label for complete information on rates and timing.

On Red Delicious apples, manganese toxicity can occur on coarse-textured soils when the soil is very acid (pH below 5.0). The symptoms known as "measles" are raised pimples on the bark underlain by dark brown spots. Other visual symptoms are leaf chlorosis, tip dieback, early leaf abscission, reduced flower bud development and shoot growth. Correction is sometimes possible by addition of lime to raise the soil pH. If possible, it should be worked into the soil. Soil sampling and addition of lime if pH is low is recommended prior to planting.

| Top of Page |

Iron (Fe)

Iron deficiency, commonly termed "lime-induced chlorosis," is not widespread in Ontario orchards. Occasionally, 1 or 2 trees in an orchard may exhibit iron-deficiency symptoms. Often these trees are located near the site of previous lime or building plaster storage, etc., where the soil pH is abnormally high. Iron deficiency causes interveinal chlorosis of new leaves. As the condition becomes more severe, the whole leaf becomes pale yellow. Quite often only one side or one branch of the tree is affected. Iron chelates1 have made correction of iron deficiency relatively easy. These materials can be applied safely as foliar sprays. Consult manufacturer's label for information on rates and timing.

| Top of Page |

Zinc (Zn)

Zinc deficiency has been identified in some apple orchards in eastern Ontario. The symptoms of this deficiency are short internodes, small narrow leaves, interveinal chlorosis with shoot and branch dieback. In advanced stages, small, narrow terminal leaves are arranged in whorls or "rosettes", giving rise to the typical "rosette" and "little leaf" description for zinc deficiency. Except in severe cases, only a few shoots on an otherwise normal tree will show symptoms. Leaf Zn levels below 15 ppm indicate a deficiency. Zinc sulfate supplying 3.6 kg of Zn/1000 L water as a dormant spray in early spring is effective. Dilute sprays in June of zinc sulfate or chelate containing 0.35 kg Zn/ha (1 kg 36% ZnSO4 or 5 L 6.5% Zn chelate) are effective in correcting zinc deficiency on fruit trees. A fungicide for disease control that contains available zinc can be an asset in orchards that are continually low in zinc. Consult manufacturer's label for available zinc concentrations in the formulation.

Learn more:

• OMAFRA Horticulture Crops Newsletters
• Publication 360, Fruit Production Recommendations
• Pub.811 Agronomy Guide for Field Crops: Chapter 2 - Soil Management and Fertilizer Use
• The Phosphorus (P) and Potassium (K) Soil Testing and Fertilizer Recommendation System in Ontario
• Soil Management and Fertilizer Use: Fertilizer Recommendations: Soil Acidity & Liming
• Sources of Agricultural Limestone
• Publication 611, Soil Fertility Handbook
• Soil Management and Fertilizer Use: Soil Testing
• Soil Management
• Soil and Water Management
• Best Management Practices Order Form
• Micronutrients for Berry Crops
• Lead and Petiole Tissue Analysis