Fertilizing Grapes

Excerpts from Publication 360, Fruit Production Recommendations

1. General Soil Fertility
2. pH Requirements
3. Petiole Analysis For Grapes
4. Fertilizer for Grapes
5. Micronutrients for Grapes
6. Related Links

General Soil Fertility

It is important to prepare and test soil before planting vines. Well in advance of planting prepare the soil through tillage and adding organic matter to ensure long-term productivity of these perennial crops.

Prior to planting, ensure that nutrient levels and pH are adequate. Test the soil and apply fertilizer and lime if necessary. Preplant applications of phosphorus, potassium and lime are the most effective.

For more information on grape production, please refer to OMAFRA publication 360, Fruit Production Recommendations.

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Manure for Vineyards

A spring application of manure is beneficial in providing nutrients and organic matter to established vineyards. Manure can also be applied in the fall prior to new spring plantings.

Broadcast manure at no more than 7 tonnes/ha of poultry manure, 40 t/ha of cattle or 35 t/ha hog. Manure is extremely variable in nutrient content and should be analyzed before application. When manure is used, reduce the rate of fertilizer.

Nitrogen is mineralized over a long period of time. Perennial crops will be supplied with nitrogen during the year. This may result in poor fruit colour, excessive terminal growth and delayed hardening of the woody tissue, and make plants more susceptible to winter injury. The practice of putting manure around newly planted vines is not recommended because of potential winter injury problems.

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 vineyards a soil sample in the vine row is recommended every 3 yr to ensure the pH is at a satisfactory level. If pH is low (acidic), apply lime 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 preferred pH before establishing a new vineyard is 6.5 on sandy soils and 6.0 on clay soils. If the pH in established vineyards is above 5.6, lime is not needed. Apply lime to established vineyards when the pH on clay loam soils drops below 5.1, and on sandy soils is below 5.6. Lime raises the soil pH, reducing its acidity and also supplying calcium. Use dolomitic lime (high in magnesium) on soils low in magnesium. Rates of application vary with soil type and initial pH. The buffer pH indicates the rate of lime to apply.

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Petiole Analysis for Grapes

In established plantings, petiole analysis in grapes is the best method of determining nutrient needs. The nutrient levels in these plant tissues most accurately reflect the uptake of nutrients by the crop. Soil analysis is used in conjunction with petiole 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 vineyard conditions. Consequently, each year the nutrient levels will 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 petioles 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. These will be reflected in the leaf analysis. Further information is available in OMAFRA Factsheet Leaf Analyses for Fruit Crop Nutrition (Order No. 91-012).
For petiole analysis to be most effective, sample the same vines each year. Make adjustments to the fertilizer program on the basis of this petiole analysis.

Fertilizer requirements are adjusted to the system of soil management, vine age, rootstock, soil type and previous fertilizer applications. Growth, fruit size, colour, and storage quality must also be considered in determining the fertilizer required.

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Fertilizer for Grapes

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 to be adequate for vineyard establishment are 12-20 ppm phosphorus, 120-150 ppm potassium, 100-250 ppm magnesium, and 1,000-5,000 ppm calcium.

If the soil has been properly prepared, including deep cultivation and addition of organic matter, there should be an adequate supply of other nutrients to sustain the vine 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 vines a needed boost. High nitrogen levels can result in excessive growth and incomplete vine hardening. The use of cover crops to check late season growth in cultivated vineyards is strongly recommended, especially in new plantings. Cover crops such as Italian ryegrass, sown about July 1, will take up much of the available nitrogen in the soil and in this way have the desirable effect of checking vine growth.

Nitrogen (N)

Petiole analysis is the most accurate way to determine nitrogen requirements of grapes. In the absence of such information, 34 kg N/ha is usually sufficient for most cultivars. This nitrogen is best broadcast before the 1st cultivation or applied as early as possible in the spring in sod vineyards. Nitrogen application can be reduced or eliminated if manure is used or growth has been excessive. Foliar applications of nitrogen should be considered in some years, based on vine performance and petiole analysis.

If, because of severe winter temperatures, there has been fruit bud damage, it may be necessary to split applications. Apply the 1st application in mid-Apr. and the 2nd application, if necessary, after bloom in late May. Excessive spring rains can leach away spring applied nutrients. Apply additional fertilizer or foliar sprays after bloom. During dry springs, irrigation may be necessary to move the fertilizer into the rooting zone of the soil just before 1st bloom or immediately after petal fall.

Phosphorus (P)

Phosphorus is not required in large amounts by grapes. With few exceptions, the level of phosphorus in Ontario soils is presently adequate. 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 a vineyard. Apply phosphorus before planting a vineyard, 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 vineyard establishment and production

Potassium (K)

An excess amount of potassium can lead to deficiency of magnesium (Mg); avoid unnecessary potassium applications. Grapes require a larger quantity of potassium than tree fruits. In the absence of petiole analysis, 400 kg/ha of muriate of potash (0-0-60) every 2nd year on clay soil and 200 kg/ha every year on sandy soil may be adequate.

In cultivated vineyards, broadcast potassium before the 1st cultivation in the spring. With grapes on clay soils, apply potassium in a band to reduce potassium fixation in the soil. Potash can injure roots and trunks if applied too closely to the trunk.

Foliar application of potassium for grapes

In dry growing seasons potassium is not readily available to the plant. Where a potassium deficiency has been confirmed, foliar applications of potassium may be beneficial. Foliar potassium applied at veraison may improve fruit yield and quality.

Magnesium (Mg)

Magnesium deficiency is becoming more evident in vineyards, particularly when high rates of potash are used.

Magnesium deficiency can lead to premature fruit drop at harvest. Magnesium deficient vines have older leaves that are pale in colour, as magnesium is a part of the chlorophyll molecule. Petiole analysis is the best way to evaluate magnesium levels.

Foliar sprays of magnesium have been effective in correcting this deficiency for the current year only. For more permanent correction, soil applications of magnesium may be required. Magnesium soil test values between 100-250 ppm are considered adequate for grapes.

Fruit or foliage injury is possible from a mixture of pesticides with magnesium sulfate. It is best to apply magnesium sulfate separately or try it on a few plants first. Check manufacturer's label regarding mixing magnesium chelates with pesticides.

For long-term corrections, soil application of magnesium can be made. The response will not likely be immediate. Also, on some soil types a single, early-spring application of soil applied magnesium has not worked well. A 2nd or 3rd application the following spring may be required before the magnesium level in the plant improves. Foliar sprays are recommended for the first 2 yr, in addition to soil applications.

Dolomitic limestone can be used on acidic soils to raise the soil pH and to supply magnesium.

Calcium (Ca)

Calcium deficiency has been associated with stem and bunch breakdown of Canada Muscat and Himrod grapes. 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. Apply adequate water volume to wet the entire vine. The more calcium applied, the better the control; but high concentrations can cause foliar burning. Use CaCl₂ (77% flakes) at 4 kg/1,000 L of water from early July to mid Aug. Apply 3 sprays, 10-12 days apart. Do not apply calcium formulations containing nitrogen after the end of July or fruit quality 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 calcium is often required in a total of 4, or more, sprays. Calcium sprays may damage foliage and fruit if applied during low temperatures and wet weather. These conditions delay the drying of the spray. Injury can also occur if calcium is applied in hot (over 25 C) or humid weather.

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Micronutrients for Grapes

Deficiencies of micronutrients or trace elements are not widespread in Ontario plantings. The desirable range for micronutrients is quite narrow. More damage is possible if micronutrients are applied in excess rather than from deficiencies. For this reason, do not apply micronutrients to fruit crops unless leaf analysis or visible symptoms confirm a deficiency. Only apply the nutrient that is deficient and in sufficient quantities to correct the problem.

Boron (B)

Boron deficiency is perhaps the most common of micronutrient deficiencies. It occurs mainly on alkaline soils (pH greater than 6.5), acid soils (pH 3.5-4.5), dry soils, soils low in organic matter, or on sandy knolls. Boron deficiency can have an effect on growth and fruiting. There is currently no accredited soil test for boron in Ontario. Use a petiole analysis to check for boron deficiencies. Boron levels should be 20-60 ppm. Where a boron deficiency has been confirmed, soil or foliar applications of boron may improve boron in plant tissues. There are several sources of boron. Check the manufacturer's recommended rates and timing of applications..

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. In addition to leaf analysis, soil tests can be used to determine the status of manganese in the soil. OMAFRA soil manganese index values greater than 8 should provide adequate manganese to the crop. If manganese is required, apply as a foliar spray of manganese sulphate or chelate. Use manganese sulphate with a spreader sticker. Soil applications of manganese are not effective. Consult manufacturer's label for complete information on rates and timing.

Iron (Fe)

Iron deficiency is also called lime-induced chlorosis. As the soil pH rises over 7, or in heavily limed soils, iron becomes unavailable to plants. Occasionally, a few plants may exhibit iron-deficiency symptoms. These are often located near the site of previous lime or building plaster storage where the soil pH is abnormally high. Iron deficiency may also occur in isolated parts of the field or on a few individual plants. 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 plant is affected.

Currently there is no accredited soil test for iron in Ontario. Confirm a suspected deficiency with a petiole analysis. Generally, soil applications of inorganic iron sources are not effective in supplying iron to the crop. Iron chelates 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

Zinc

Zinc deficiency symptoms include short internodes, small narrow leaves, and interveinal chlorosis with shoot and branch die back. In advanced stages, small, narrow terminal leaves are arranged in whorls or "rosettes". This results in the typical "rosette" and "little leaf" description for zinc deficiency. In addition to petiole analysis, soil tests can be used to determine the status of zinc in the soil. An OMAFRA soil zinc index value greater than 8 provides adequate zinc to the crop. Where a zinc deficiency has been confirmed, check manufacturer's recommended rates and timing of applications of zinc products.

Warning: Do Not Concentrate Nutrient Sprays