Blueberry nutrition fertilization
Blueberry plants need many elements for normal growth. The three primary elements, nitrogen (N), phosphorus (P), and potassium (K), are used in larger quantities than the other elements. They require frequent replacement in soils from which crops are regularly harvested. Three secondary elements, calcium (Ca), magnesium (Mg), and sulfur (S), are used in smaller amounts but may require periodic replacement in some soils. These elements are replaced by adding such minerals as ground limestone, gypsum, dolomite, or powdered sulfur to the soil. A single application of these minerals usually lasts several years.
Micronutrients such as boron, manganese, copper, zinc, iron, molybdenum, and chlorine are used by plants in small amounts. Most soils contain sufficient micronutrients, so they are added only if abnormal plant response (generally foliar symptoms) or a soil or tissue analysis indicates a deficiency. Only small quantities of micronutrients are needed by plants, so they can be applied as leaf sprays, injected in the irrigation water, or added to other fertilizer applications. Blueberry plants respond more rapidly to foliar sprays of micronutrients than to soil treatments. Click here for the latest fertilizer guide.
Soil treatments last longer, but under some conditions soil-applied micronutrients are tied up and are unavailable to the plants and, therefore, foliar sprays are necessary. Certain micronutrients such as boron (B) and copper (Cu) can injure plants if applied at higher amounts than necessary for plant growth and can cause extensive damage to blueberries. The need for fertilization should be determined by soil and/or tissue analysis. A soil test should be obtained and analyzed prior to establishing the planting to determine if major adjustments are necessary. For example, soil pH may be too high for optimum blueberry production
To reduce soil pH, preplant application of amendments such as sulfur or aluminum sulfate are necessary. Application of elements such as K and Mg are more accessible to plant roots when mixed with the soil rather than broadcast over the surface after planting. On established plantings, leaf analysis is more useful than soil analysis. Use leaf analysis annually to determine plant nutrient concentration; soil analysis can be used every 3 or 4 years to monitor changes in soil pH, P, K, Ca, and Mg. Regular monitoring of soil pH should be a priority. Soil samples (exclude sawdust, if possible) should be taken from around the edge of the plants or drip line, preferably in the row between bushes. Soil should be removed from around a number of bushes at random over the area to be tested. If there is a problem area in the field, obtain a sample from this area alone; take a separate sample from an area where the plants are growing normally. Note that sampling for nematodes requires a different procedure (see Sampling for Nematodes). If annual growth or leaf symptoms are present, describe them and include a description with the soil samples. Cartons and soil sample instructions can be obtained from your local county Extension office. If a number of samples are being sent, code them by numbering each sample. Keep a record of the area where each sample was obtained.
A standard soil test will include pH, percent organic matter, parts per million of P and K, and milliequivalents per 100 grams of soil of Ca and Mg. Also ask for parts per million of B, cation exchange capacity (CEC), and percent base saturation. Ask your county Extension office for an interpretation and recommendations. Soil tests are not useful for N; the best measure for N requirement is by observing the amount of vegetative growth and fruit production, and by leaf analysis. When soil sampling an established blueberry planting, keep in mind that soil pH differences will occur throughout the field. Close to the plants, where N fertilizers are applied, the pH will be lower than between the rows.
For leaf analysis, collect the most recent fully expanded leaves from fruiting shoots in late July to mid-August. Sample 5 leaves from each of 10 plants randomly throughout the field. Cultivars should be sampled separately. Rinse the leaves and dry them rapidly. Collecting one sample from affected plants and another from apparently healthy plants is often useful. Soil and tissue analyses can be performed by numerous laboratories. See your local county Extension office for details. pH Harmer (1944) established a soil pH range of 4.0 to 5.2, with an optimum of 4.5 to 4.8, for blueberry growth and production. If the pH is above this range, use elemental sulfur or aluminum sulfate to reduce pH according to table 1.
Table 1. Amount of elemental S needed to lower soil pH to 4.5 (1)
|Current pH||Sandy Soil (lbs/A)||Loam (lbs/A)||Clay Soil (lbs/A)|
(1) To substitute aluminum sulfate, multiply by 6. Keep in mind that use of ammonium sulfate fertilizer as a source of N will lower the soil pH.
Nitrate fertilizers, however, have little effect on soil pH. If the pH is below 4.0, use lime (see Calcium and Magnesium). Nitrogen (N) Adequate N levels are necessary to maintain renewal growth, crop production, and flower bud development for next year’s crop. Excess N leads to excessive vegetative growth; development of immature wood late in the season, increasing risk of winter injury; restricted flower bud formation; and delayed fruit maturity. Blueberry plants that do not have sufficient N show reduced size, poor leaf color, weak or stunted growth, and stopping of growth before the end of the season. A deficiency of N serious enough to cause reddening of the foliage will stop growth and reduce yield. Soil testing for N is not a reliable indicator of perennial crop N status.
Leaf analysis alone (table 2) does not indicate whether N fertilization is required, but can be used in conjunction with an assessment of plant growth and productivity to determine N status.
Table 2. Blueberry N fertilizer rate per plant and per acre from establishment (year 1) to maturity
(1) Assuming 1,000 plants/A. The overall vigor of the plant is the best indication of N status. Nitrogen concentration should be interpreted with an assessment of vigor. Above normal N and high vigor indicate over-fertilization of N. Below normal N and low vigor indicate a need for additional nitrogen. Above normal N and low vigor suggest another growth-limiting factor. Below normal N and high vigor can occur on bushes with little or no crop (table 3).
Table 3. Blueberry leaf N sufficiency, late July to mid-August sampling
|% Dry Weight||Leaf N Status|
|1.51 – 1.75||below normal|
|1.76 – 2.00||normal|
|2.01 – 2.50||above normal|
Common N fertilizers available include: ammonium sulfate (21-0-0) [(NH4)2SO4], ammonium nitrate (34-0-0) [NH4NO3], and urea (46-0-0) [CO(NH2)2].
Both the ammonium and nitrate forms of N can be used if the pH is less than 5.5. However, above pH 5.5 the ammonium form is favored. Fertilizers which contain only nitrate (e.g. calcium nitrate) may cause injury or reduced growth and should be avoided. Additionally, urea nitrifies rapidly when the soil pH is above 5.5. Therefore, urea use is recommended only when the soil pH is below 5.5. Any N fertilizer should be incorporated by rain or an irrigation within 1 to 2 days of surface application.
Nitrogen rates presented in tables 2 and 4 are based on research and grower experience. Apply from 80 to 140 lbs N/A to mature plantings. Adjust fertilization based on plant age, plant spacing, N status, and visual observation of vigor and productivity.
Table 4. N fertilizer rate for mature plants adjusted for spacing (1)
|Spacing (ft)||Plants/A||N Rate (lbs/A)|
|5 x 8||1,089||100|
|5 x 7||1,244||125|
|3 x 10||1,452||150|
(1) Rate = [43,560 ft squared/A – (row x plant spacing)] x oz N/plant.
Broadcast fertilizer under the plant canopy. There is very little lateral nutrient translocation within the plant, so fertilize both sides of the plant row to insure even growth. Yields may be higher if the fertilizer is split. Split applications allow plants more time to absorb the nutrients before they are lost by leaching. Apply half before bud break in the spring and half about 6 weeks later. Some growers split N into three equal portions. Make the third application no later than July 1, and irrigate. Some growers supplement annual soil applications of N with foliar sprays during the season.
Supplemental N sprays may be beneficial on N deficient bushes, but bushes receiving appropriate soil applications of N are unlikely to respond to sprays. Sawdust mulched plantings may need 50 to 100 percent more N depending on the degree of sawdust decomposition. Martin and Pelofske (1983) showed highest yield of mulched Bluecrop plants when 125 lbs N/A was applied during the first two production years. In subsequent years, yield was the same at the 75 and 125 lb rates, suggesting that there is less need for N as sawdust ages. Phosphorus (P) Phosphorus deficiency is generally noted by a deep, purplish-green color on the tip of leaves and a dark purple appearance of basal leaves. This is distinct from the reddening produced by lack of N or lack of moisture.
Leaves have a purplish cast and generally have a leathery texture. This color is not confined to mature leaves, but also occurs on the tips of the growing shoots. This symptom is at times affected by the amount of light coming into the plant. Under bright sunlight, the purple coloration is very easily seen. Under shaded or cloudy conditions it may disappear. The angle of the leaf to the stem is very narrow; occasionally the leaves will be pressed against the stem. Symptoms of P deficiency have rarely been seen in the field. Effects from excessive P are also rare. A guide for P application is given in table 5. Various fertilizers can be used, such as triple superphosphate (0-45-0) or ammonium phosphate/sulfate (16-20-0-15).
Plantings in Idaho may require much higher applications of P. Check with your local county Extension agent.
Table 5. Phosphorus fertilization rates based on soil and late July to mid-August tissue sampling
|Soil P (Bray Method) (ppm)||Leaf P (%)||Phosphate (lbs/A)|
|0 – 25||Under 0.20||40 – 60|
|25 – 50||0.21 – 0.40||0 – 40|
|Over 50||0.41 – 0.70||0|
Potassium (K) Potassium deficiency is first indicated by death of the terminal growing points followed by dead spots just inside the leaf edges and, with increased severity, scorching of edges on the older leaves.
Occasionally, on the youngest leaves, there is yellowing between veins, similar to iron (Fe) deficiency. Sometimes a shoot will grow for a time and then suddenly stop and the growing point will die. If these terminals are examined, the very tip leaflet of the shoot will be black. There is, at times, subsequent branching from lateral buds. They, too, may grow for a time, develop interveinal yellowing, and then die at the tip. Potassium deficiency is relatively rare in the Pacific Northwest. Low leaf K values may be caused by poor drainage, drought, or very acid soils.
Crop load also has a strong influence on leaf K levels. Ballinger (1966) found that the percentage of K in the berry increased dramatically as fruit matured, averaging over 60 mg per berry when ripe. Thus, deficiency levels in leaves may occur in years with a heavy crop load and normal levels may return after harvest. Normal August leaf levels are 0.41 to 0.70 percent. If a below-normal leaf value occurs, use trial applications of 150 lbs/A potassium sulfate (0-0-52) [K2SO4], banded. Avoid muriate of potash (potassium chloride), as chloride may cause reduced growth and injury to blueberries.
If both K and Mg are needed, use 400 lb/A sulfate of potash-magnesia (0-0-21, 11% S, 10% Mg) [K2SO4, MgSO4]. Blueberry yields have been shown to increase by K fertilization on various soil types if values are deficient. Use Table 6 as a guide for K application.
Table 6. Potassium fertilization rates based on soil and late July to mid-August tissue sampling Soil Test
|K (ppm)||Tissue K (%)||Potassium (lbs/A)|
|0 – 100||less than 0.20||75|
|101 – 150||0.21 – 0.40||50|
|Over 150||0.41 or more||25|
Excess K can interfere with uptake of other elements, especially Mg.
Therefore, do not apply K unless foliar analysis indicates a deficiency. Both P and K are immobile. Placement in the root zone will enhance uptake. If possible, shank these elements into the soil area near the root zone in late fall or spring prior to bud break. When N is included with P and K, apply in spring. When shanking is not possible, topdress fertilizer. Irrigate if it does not rain in 1 to 2 days. Calcium (Ca) and Magnesium (Mg) Calcium deficiency symptoms are very inconclusive.
The most noticeable symptom is a marginal yellowing and scorching of the leaves. Marginal yellowing is also a symptom of Blueberry Scorch Virus infection. Terminal leaves show a slight yellowish-green blotchiness to yellow edges and, occasionally, a tendency toward rosetting (the internodes are very short). The tips of basal leaves become scorched and later may break off. Although blueberries are seldom deficient in Ca, variations in leaf Ca occur. High Ca concentration may be an indication of high soil Ca or high crop load. Low leaf Ca concentration may be present in heavily fertilized, vigorously growing plants or be a result of low soil pH.
If low soil pH is suspected, check tissue Manganese concentration. Abnormally high Manganese (above 450 ppm) is an indication of low soil pH and low soil Ca. Normal blueberry tissue Ca is from 0.41 to 0.8 percent. If Ca is required and pH is below 4.0, topdress 1 T/A limestone (Ca), or dolomitic limestone (Ca + Mg) if Mg is needed as well. If Ca is needed and the pH is above 5.0, apply 1 T gypsum/A. Magnesium deficiency can be recognized by the bright red edges of older leaves.
The red coloration along the edges between the veins is in strong contrast to the green which prevails along the center mid-rib. The green area frequently has a shape somewhat like that of a Christmas tree. Other symptoms, such as dead spots and shades of yellow or brown in place of red, depend on the intensity of sunlight.
For the most part, under field conditions, the red coloration and the Christmas tree green areas in the center of the leaf are characteristic. Symptoms occur on the older leaves first and on the lower part of the bush. Normal leaf Mg levels are in the range of 0.13 to 0.25 percent. Excessive leaf Mg may indicate a high soil pH. If Mg is needed and the pH is above 5.0, apply magnesium sulfate (epsom salts) or Sul-Po-Mag (21% K, 11% S, 10% Mg) at 500 lbs/A. If the pH is below 4.0 and Mg is required, apply 1 T/A dolomite lime. The addition of approximately 4% Mg to the regular fertilizer program will help maintain Mg levels in the soil.
Soil testing every 3 to 5 years allows moni-toring of changes in soil Mg or Ca levels. Applications of lime, gypsum, dolomite, and magnesium sulfate should be made in the fall to permit an adequate time for interaction with the soil before the growing season. Lime reacts best when mixed with the soil. This is only practical prior to planting. Topdressed lime changes soil pH gradually.
Monitor leaf Manganese after liming, as it should decrease. Sulfur (S) Sulfur is an essential element but is more commonly applied to blueberries to reduce soil pH than to correct a nutrient deficiency. Normal leaf levels for S range from 0.11 to 0.16%. Boron (B) Boron deficiency in blueberries is recognized by a bluish color of the terminal leaves, which suddenly stop growth.
This is followed by slight yellowing between leaf veins and yellowish spotting along the edges of the younger leaves just below the growing point. Leaves become distorted, often develop a cup-shaped appearance, growth ceases, and shoots die at the tip.
Shoot die-back is probably the most common symptom in boron-deficient blueberries. The die-back at times creates a witches’-broom, since branches develop lower down on green tissue and, in turn, die if the deficiency is not corrected. Leaf and fruit buds may fail to develop in severely deficient plants. Fruit set may be reduced. Winter injury may also be greater on B deficient plants.
Boron deficiency is relatively common in Oregon and Washington. Use the leaf tissue levels in table 7 as a guide for B application.
Table 7. Blueberry leaf B sufficiency, late July to mid-August sampling
|Leaf B (ppm)||Status|
|21 – 30||below normal|
|31 – 80||normal|
|81 – 150||above normal|
If B is deficient, apply either Solubor(20% B) at 2 to 6 lbs product/100 gallons water/A or 10 to 20 lbs/A Borax (11% B).
Solubor should be applied as a foliar spray prior to bloom or after harvest. Apply Borax in the fall or early spring prior to rain.
Many blueberry growers in Oregon follow an annual B application program of one-half lb B/A. Leaf levels should be monitored carefully excess B is toxic to plants. Zinc (Zn) Symptoms of Zn deficiency include small leaves, with the youngest leaves somewhat yellow and folded upwards along the mid-rib, and short internodes. Excessive use of P will sometimes create Zn deficiency symptoms.
Deficiency is less common if pH is below 6.0. Normal leaf concentrations are between 8 to 30 ppm. If plants are deficient: apply Zn chelate (14% Zn) as a foliar spray at 1 lb/100 gallons water/A prior to bloom or after harvest, or apply 10 to 30 lbs/A Zn chelate or 10 to 30 lbs/A Zn sulfate (36% Zn) to the soil. Copper (Cu) Symptoms of Cu deficiency include yellowing between the veins of young leaves and a possible die-back of young shoots. Cu deficiency may be more common in soils with high concentrations of organic matter. Normal leaf levels for Cu are from 5 to 15 ppm. If tissue concentration is low, use a trial application of copper sulfate (25% Cu) at 30 to 50 lbs/A to the soil, or a foliar application of 1 lb/100 gallons water/A. Cu is very toxic at an excessive rate, so use caution and experiment on a few plants before applying to the entire field. Toxicity may occur at leaf levels higher than 20 ppm.
Iron (Fe) Iron deficiency in leaves is often the result of a high soil pH rather than Fe deficiency in the soil. Symptoms of Fe deficiency include yellowing between leaf veins, appearing first on the younger leaves. Shoot growth and leaf size are sometimes reduced. Normal leaf values for Fe are from 61 to 200 ppm. If levels are deficient, apply iron chelate (10% Fe) at 2 lbs/100 gallons water/A twice to leaves (see label) or 15 to 30 lbs/A to the soil. A soil application of 10 to 20 lbs/A ferrous sulfate (34% Fe) is also suitable.
Fertilizer Applications Nutrients in fertilizers are carried down to the root area by rainfall or irrigation. Too much highly soluble fertilizer, such as ammonium sulfate or potassium sulfate, concentrated in a small area above the roots, will injure them. Leaching may also be a problem when too much highly soluble fertilizer is applied at once. Spread fertilizer evenly over the outer edge of the root zone in a band under the plant canopy.
The root zone generally extends to the outer edge of the branches (drip line) or slightly beyond. Fertilizer spreaders well suited for this purpose are available. There is very little lateral nutrient translocation within the plant, so fertilize both sides of the plant row to ensure even growth. Rainfall usually will be adequate to carry the early spring (bud break) fertilization down to the root zone. Late spring (May) and summer (July) applications of fertilizer should be followed by irrigation where possible.
Fertilizer can be side-dressed by placing it 2 to 3 inches below the soil surface at the outer edge of the root zone. Side-dressing too close to the blueberry plant will seriously injure the roots. Finally, fertilizer application should be adjusted for crop load as nutrients are removed in the fruit (table 8).
Table 8. Amount of nitrogen, phosphorus, and potassium removed with the fruit of Wolcott as affected by crop load (from Ballinger and Kushman, 1966)
|Lbs/A Removed (6-year-old Wolcott)|
Organic Materials Blueberries may be fertilized with organic materials available (tables 9 and 10). Table 11 lists materials that will lower soil pH.
Table 9. Nutrient content of organic materials used for macronutrient supplementation Materials Percent(1)
|Nitrogen Percent||Phosphate||Relative Potassium Availability||animal tankage (dry)|
|7||10||0.5||medium bone meal (raw)|
|2-6||15-27||0.5||medium bone meal (steamed)|
|0.7-7||18-34||0||slow -medium castor pomace|
|5||1.8||1||slow coca shell meal|
|2.5||1||2.5||slow cottonseed meal (dry)|
|4-6||2.5-3||1.6||slow – medium compost (not fortified)|
|1.5-3.5||0.5-1||1-2||slow – medium dried blood (dry)|
|12||1.5||0.6||medium – rapid fertrell-blue label|
|1||1||1||slow fertrell-gold label|
|3||3||3||slow fertrell-super N|
|4||3||4||slow fish meal (dry)|
|10||4-6||0||slow fish scrap (dry)|
|3.5-12||1-12||0.1-1.6||slow garbage tankage (dry)|
|2.7||3||1||very slow guano (bat)|
|5.7||8.6||2||medium guano (Peru)|
|12.5||11.2||2.4||medium kelp (2)|
|0.9||0.5||4-13||slow manure (3) (fresh) cattle|
|0.3||0.3||0.3||medium poultry (4)|
|0||1.5||2||very slow tobacco stems (dry)|
|2||0.7||6||slow urea (5)|
|42-46||0||0||rapid wood ashes (6)|
(*) Some of the materials may not be available because of restricted sources.
(1) The percentage of plant nutrients is highly variable and with some materials mean percentages are listed.
(2) Contains common salt, sodium carbonates, sodium and potassium sulfates.
(3) Plant nutrients available during year of application. Varies with amount of straw and method of storage.
(4) Contains calcium.
(5) Urea is an organic compound, but since it is synthetic it is doubtful that most organic gardeners would consider it acceptable.
(6) Potash content depends on the tree species burned. Wood ashes are alkaline, containing approximately 34% CaO.
Table 10. Natural deposits useable as fertilizers
|Percent (1)||Nitrogen Percent (1)||Phosphate Percent (1)||Potassium Relative Availability||colloidal phosphate|
|0||20-32||0||very slow||sodium nitrate|
(1) The percentage of plant nutrients is highly variable and differs with place of origin. The availability of plant food from natural deposits depends largely upon the fineness to which these materials are pulverized.
Table 11. Organic materials used to decrease soil acidity
|clam shells (finely ground)||50% CaO|
|clam shells (75% shall pass a 100-mesh sieve)||35 – 42% CaO|
|oyster shells||43 – 50% CaO|
|wood ashes||32% CaO|
|dolomitic limestone||15% MgO + 35% CaO|
|calcitic limtstone||45 – 50% CaO|
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University.