{"id":34791,"date":"2026-06-02T19:57:02","date_gmt":"2026-06-02T23:57:02","guid":{"rendered":"https:\/\/extension.umaine.edu\/publications\/?page_id=34791"},"modified":"2026-06-03T13:05:35","modified_gmt":"2026-06-03T17:05:35","slug":"2383e","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/publications\/2383e\/","title":{"rendered":"Bulletin #2383, Fertilizing Wild Blueberry Fields"},"content":{"rendered":"\n<p><em>By Lily Calderwood, Ph.D., wild blueberry specialist and associate professor of horticulture, University of Maine Cooperative Extension; Leala Machesney, Extension and research professional, University of Maine Cooperative Extension and Jordan Parks, wild blueberry research technician, University of Maine Cooperative Extension<\/em><\/p>\n\n\n\n<p><strong>For information about UMaine Extension programs and resources, visit <a href=\"https:\/\/extension.umaine.edu\/\">extension.umaine.edu<\/a>.<\/strong><br><strong>Find more of our publications and books at <a href=\"https:\/\/extension.umaine.edu\/publications\/\">extension.umaine.edu\/publications\/<\/a>.<\/strong><\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Introduction<\/strong><\/h3>\n\n\n\n<p>Fertilizer provides essential nutrients used for wild blueberry growth, health, and fruit production. Properly fertilized plants will be better able to withstand stress such as disease, drought, and harsh winter conditions. Farming wild blueberries in the accepted 2-year production cycle is challenging because after growing prune-year stems and buds, weather events or animal damage can occur over the winter and the following season. Today, fertilizer in wild blueberry production is applied during the spring of the prune-year. It can increase the number and quality of flower buds, in addition to increasing stem height and density. This can lead to greater yields, assuming that production goes well the following crop-year. Because of this, it is important to focus on prune-year fields. The benefits of fertilizing wild blueberry fields apply to both organic and conventional management plans.<\/p>\n\n\n\n<p>In this bulletin we describe:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Testing soil and leaves to inform fertilizer type and rate<\/li>\n\n\n\n<li>Different types of fertilizer for wild blueberry<\/li>\n\n\n\n<li>How to calculate fertilizer rates<\/li>\n\n\n\n<li>Summary of our research efforts to increase our understanding of how fertilizer works in the wild blueberry production system<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Before Fertilizing Your Field<\/strong><\/h3>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Control Weeds<\/strong><\/h4>\n\n\n\n<p>Weeds compete with wild blueberry plants for light, moisture, and nutrients. They also lower blueberry yields, split berries during harvest, and get caught in harvesting machines, making it imperative to achieve good weed control before applying fertilizer. This is why most organic producers do not consider applying fertilizer. However, once soil pH is low (4.0\u20134.3) and weeds are controlled, organic producers can consider fertilization. Research on weed control in wild blueberry can be found in <a href=\"https:\/\/extension.umaine.edu\/blueberries\/resources\/weeds\/weed-management-in-wild-blueberry-fields\/\">UMaine Extension Bulletin 2193: Weed Management in Wild Blueberry Fields<\/a>, which provides several tactics to help growers achieve their goals.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Collect Foliar Samples<\/strong><\/h4>\n\n\n\n<p>Foliar samples taken in the prune-year will indicate nutrient deficiencies that can be corrected with a fertilizer application in the spring of the next prune-year (Table 1). Failure to take these samples and understand the results can lead to over- or underapplication. Overapplying fertilizer can cause the farmer to spend more money than necessary, can cause the plants to produce too much vegetation and too little fruit, and can leach nutrients into waterways, which can be harmful to fish and other aquatic life. Underapplying fertilizer can reduce your yield.<\/p>\n\n\n\n<p><strong>Standard Range for Foliar Nutrient Levels of Wild Blueberries<\/strong><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table><thead><tr><th scope=\"col\">Element<\/th><th scope=\"col\">Minimum<\/th><th scope=\"col\">Maximum<\/th><th scope=\"col\">Optimum<\/th><\/tr><\/thead><tbody><tr><th scope=\"row\">Nitrogen (N)<\/th><td>1.55%<\/td><td>1.85%<\/td><td>1.76%<\/td><\/tr><tr><th scope=\"row\">Phosphorus (P)<\/th><td>0.111%<\/td><td>0.143%<\/td><td>0.136%<\/td><\/tr><tr><th scope=\"row\">Potassium (K)<\/th><td>0.31%<\/td><td>0.56%<\/td><td>0.44%<\/td><\/tr><tr><th scope=\"row\">Calcium (Ca)<\/th><td>0.31%<\/td><td>0.40%<\/td><td>0.38%<\/td><\/tr><tr><th scope=\"row\">Magnesium (Mg)<\/th><td>0.16%<\/td><td>0.18%<\/td><td>0.17%<\/td><\/tr><tr><th scope=\"row\">Boron (B)<\/th><td>2 ppm<\/td><td>44 ppm<\/td><td>23 ppm<\/td><\/tr><tr><th scope=\"row\">Iron (Fe)<\/th><td>34 ppm<\/td><td>37 ppm<\/td><td>35 ppm<\/td><\/tr><tr><th scope=\"row\">Manganese (Mn)<\/th><td>710 ppm<\/td><td>2637 ppm<\/td><td>963 ppm<\/td><\/tr><tr><th scope=\"row\">Zinc (Zn)<\/th><td>10 ppm<\/td><td>15 ppm<\/td><td>13 ppm<\/td><\/tr><tr><th scope=\"row\">Copper (Cu)<\/th><td>3 ppm<\/td><td>6 ppm<\/td><td>4 ppm<\/td><\/tr><tr><th scope=\"row\">Molybdenum (Mo)<\/th><td>1.20 ppm<\/td><td>3.30 ppm<\/td><td>0.33 ppm<\/td><\/tr><tr><th scope=\"row\">Aluminum (Al)<\/th><td>98 ppm<\/td><td>289 ppm<\/td><td>179 ppm<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p><strong>Table 1.<\/strong> Standard ranges for foliar nutrients in wild blueberry production. When you receive your leaf sample results, the soil lab personnel have compared your nutrient levels to those in this table and provided you with a recommended fertilizer rate. Sources: Santiago, 2011; Trevett 1972<\/p>\n\n\n<style>.kb-image34791_2d509b-c5.kb-image-is-ratio-size, .kb-image34791_2d509b-c5 .kb-image-is-ratio-size{max-width:400px;width:100%;}.wp-block-kadence-column > .kt-inside-inner-col > .kb-image34791_2d509b-c5.kb-image-is-ratio-size, .wp-block-kadence-column > .kt-inside-inner-col > .kb-image34791_2d509b-c5 .kb-image-is-ratio-size{align-self:unset;}.kb-image34791_2d509b-c5 figure{max-width:400px;}.kb-image34791_2d509b-c5 .image-is-svg, .kb-image34791_2d509b-c5 .image-is-svg img{width:100%;}.kb-image34791_2d509b-c5 .kb-image-has-overlay:after{opacity:0.3;}.kb-image34791_2d509b-c5 img.kb-img, .kb-image34791_2d509b-c5 .kb-img img{object-position:50% 50%;}<\/style>\n<div class=\"wp-block-kadence-image kb-image34791_2d509b-c5\"><figure class=\"alignright size-large kb-image-is-ratio-size\"><div class=\"kb-is-ratio-image kb-image-ratio-land43\"><img loading=\"lazy\" decoding=\"async\" width=\"768\" height=\"1024\" src=\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-768x1024.jpg\" alt=\"An image showing tip-dieback at the top of a stem. The top leaf shrivels, turns brown, and dies at the end of June or beginning of July. This indicates that the stem is now putting energy into developing branches and buds instead of vegetative growth.\" class=\"kb-img wp-image-34819\" srcset=\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-768x1024.jpg 768w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-225x300.jpg 225w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-1152x1536.jpg 1152w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-1536x2048.jpg 1536w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-105x140.jpg 105w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-317x423.jpg 317w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-423x564.jpg 423w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-634x845.jpg 634w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-846x1128.jpg 846w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-951x1268.jpg 951w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-1268x1691.jpg 1268w, https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-scaled.jpg 1920w\" sizes=\"auto, (max-width: 320px) 85vw, (max-width: 768px) 67vw, (max-width: 1024px) 62vw,768px\" \/><\/div><figcaption><strong>Image 1.<\/strong> An image showing tip-dieback at the top of a stem. The top leaf shrivels, turns brown, and dies at the end of June or beginning of July. This indicates that the stem is now putting energy into developing branches and buds instead of vegetative growth. Foliar samples should be taken at this time. Photo credit: Leala Machesney.<\/figcaption><\/figure><\/div>\n\n\n\n<p>Foliar samples should be collected at the tip-dieback stage in late June to early July when plant nutrients are most stable (Image 1). Historically, tip-dieback has occurred around the 4th of July in Maine, but today this stage often occurs in late June. At this stage, the plant is triggered by day length to transition from vegetative growth to branch and bud production. Wild blueberry fields that are fertilized regularly maintain their health for more consistent yields and are better able to withstand stress. For more information on how to collect foliar samples, please see <a href=\"https:\/\/extension.umaine.edu\/publications\/2382e\">UMaine Extension Bulletin #2382: Leaf and Soil Testing for Wild Blueberry Fields<\/a>.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Collect Soil Samples<\/strong><\/h4>\n\n\n\n<p>Soil samples taken in the spring of either the prune- or crop-year will indicate the soil condition measured by soil pH, percent organic matter (% OM), and cation exchange capacity. Wild blueberry soil is acidic and is naturally low in nutrients. The optimum soil pH for most wild blueberry is 4.3, which is acidic enough to reduce weed pressure but not so acidic that the wild blueberry plants cannot take up any nutrients. As soil pH declines, fewer positively charged nutrients are available for plants to take up. However, mycorrhizal fungi, present in all wild blueberry soils, partner with wild blueberry roots to deliver nutrients and water to the blueberry in exchange for carbohydrates.<\/p>\n\n\n\n<p>Soil organic matter is present on the surface of wild blueberry soils, and the bulk of wild blueberry roots live in this 1- to 3-inch-deep organic matter zone. In wild blueberry soils, organic matter ranges from 8% to 20%, which is high for agricultural soils. Organic matter is the only source, or storage place, for nutrients in the soil. In general, acidic wild blueberry soils have fungal, rather than bacterial, communities and no earthworms are present. We do not yet know how much fertility you can expect your plants to receive from organic matter in the wild blueberry system.<\/p>\n\n\n\n<p>Cation exchange capacity is the nutrient storage capacity of your soil. In clay soils or soils with high organic matter content, CEC will be high; therefore, it can retain more fertilizer and sulfur. In sandy soils or soils with low organic matter content, CEC will be low, and fertilizer and sulfur will be more likely to leach down through the soil profile and be unavailable for plant use. Soils with high CEC can hold onto more fertilizer and sulfur, while low CEC soils require more frequent applications of smaller amounts. CEC is important to know if you are not seeing the expected results from either fertilizer or sulfur applications.<\/p>\n\n\n\n<p>Collect soil samples in the spring of the prune- or crop-year. Complete the UMaine Soil Testing Lab Form using code 400 for wild blueberry. For prune fields, it may be convenient to collect soil samples as you are collecting foliar samples at the tip-dieback stage in late June or early July. For more information on how to collect soil samples, please see <a href=\"https:\/\/extension.umaine.edu\/publications\/2382e\">UMaine Extension Bulletin #2382: Leaf and Soil Testing for Wild Blueberry Fields<\/a>.<\/p>\n\n\n\n<p>Once the foliar and soil samples have been collected and delivered to the University of Maine Soil Testing Lab in Orono, the lab will conduct tests on the samples to provide you with values and recommendations for the type of fertilizer and the rate required for adequate fertilization. To interpret the foliar sample results, please read <a href=\"https:\/\/extension.umaine.edu\/publications\/2093e\">UMaine Extension Bulletin 2093: Interpreting Your Leaf Analysis Results<\/a>. This bulletin will show you the optimal nutrient ranges for wild blueberries and how to identify deficiency symptoms in your plants. After this information has been collected, it is time to plan a fertilizer application based on the results of the foliar and soil tests.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Types of Nutrients and Fertilizers for Acidic Soils<\/strong><\/h3>\n\n\n\n<p>The results of your soil and foliar analysis may indicate that your wild blueberry plants are deficient in nitrogen, or both nitrogen and phosphorus, and that the soil pH is above optimum for wild blueberry production. These nutrient deficiencies, soil pH levels, and whether plants are managed in a conventional or organic system will guide the appropriate fertilizer selection.<\/p>\n\n\n\n<p>Nitrogen, phosphorus, and potassium are the major nutrients that plants require (the three numbers on a fertilizer bag indicate the percentage of each in the bag: N-P-K). Nitrogen (N) is the building block of green material (leaves, buds, flowers, and fruit) that plants draw upon for energy. Phosphorus (P) can be seen as a structural building block, and especially helps to improve rhizome, stem, and branch strength. Potassium (K) is necessary but not typically applied in the wild blueberry system. This is because K+ competes with ammonium (NH4+) for negatively charged soil space. Ammonium is the form of N that blueberry plants can absorb. Additionally, excess K in leaves can decrease leaf calcium (Ca+), another important positively charged nutrient (Espinoza et al., 2025). Ca+ is important for reducing fruit drop and improving fruit firmness (Calderwood et al., 2026). When soil pH is low, there are many H+ ions in the soil, creating competition for positively charged nutrients to latch on to negatively charged soil space. Typically, this means that the lower your soil pH, the more difficult it will be for plants to take up positively charged nutrients. You can have the University of Maine Soil Testing Lab in Orono measure your soil\u2019s CEC to understand how well your soil type can hold onto positively charged fertilizer ions.<\/p>\n\n\n\n<p>Below we discuss commonly used fertilizers for wild blueberry fields and their typical nutrient analysis.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Ammonium Sulfate (AS) (21-0-0, 24%S)<\/strong><\/h4>\n\n\n\n<p>Apply ammonium sulfate [(NH4)2(SO4)] to wild blueberry fields if the result of foliar testing indicates low nitrogen. Although ammonium sulfate contains some sulfur, it does not contain enough to lower soil pH, and additional sulfur should be applied to lower soil pH to 4.3. The reason ammonium sulfate contains sulfur is to compensate for the natural rise in soil pH seen from any nitrogen fertilizer. This fertilizer is made for acid-loving crops and is the most used fertilizer in highbush blueberry production. In wild blueberry production, ammonium sulfate is applied in two scenarios: (1) when P levels are optimal and the farmer wants to apply only N, or (2) when optimizing yield, it is applied in addition to a monoammonium phosphate or diammonium phosphate application to provide P and additional N.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Monoammonium Phosphate (MAP) (11-52-0)<\/strong><\/h4>\n\n\n\n<p>Apply MAP [(NH4)(H2PO4)] if the results of foliar testing indicate your plants are deficient in both nitrogen and phosphorus. MAP has an acidifying effect on soil, making it an ideal fertilizer choice for wild blueberries that thrive in soil pH levels between 4.0 and 4.5. However, it can often be more costly per unit compared to DAP and has a slightly lower nitrogen content.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Diammonium Phosphate (DAP) (18-46-0)<\/strong><\/h4>\n\n\n\n<p>Apply DAP [(NH4)2(HPO4)] if the results of foliar testing indicate your plants are deficient in nitrogen and phosphorus. DAP slightly raises the pH of your soil immediately after application but eventually does acidify the soil. In the short term, as DAP granules dissolve, wild blueberry plants could become stressed if the soil pH is already high before DAP application. However, DAP does contain slightly more nitrogen than MAP and is often less expensive. When choosing between DAP and MAP, DAP is best reserved for situations where an initial pH boost is not a risk and more initial nitrogen is required.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Urea (46-0-0)<\/strong><\/h4>\n\n\n\n<p>Urea [CO(NH2)2] has been used on wild blueberry fields in the past. It is affordable but volatile and can burn plants if the application rate is too high. Urea turns into ammonium and carbon dioxide when exposed to water. Urea is typically used on tilled agricultural land, which incorporates the urea into the soil. Wild blueberry fields are not tilled, leaving urea on the soil surface, which will cause significant losses in nitrogen, resulting in a wasted investment.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Pelleted Chicken Manure (Organic 5-4-3)<\/strong><\/h4>\n\n\n\n<p>Pelleted chicken manure is a suitable fertilizer for organic wild blueberry fields once weed competition is low. It is important to apply chicken manure that is not \u201chot\u201d because human pathogens such as E. coli can be present in fresh manure. Use only pelleted chicken manure that has been composted at 131\u00b0F\u2013170\u00b0F for 15 days, as required by the National Organic Standard. This process kills many pathogens and breaks down the compounds that can burn plants. Chicken manure is high in organic matter and considered to be a slow-release fertilizer, which means it will take longer to make its way to plant roots than conventional fertilizers, but plants will green up within a few weeks of application.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Calculating Fertilizer Rates<\/strong><\/h3>\n\n\n\n<p>Once a fertilizer is selected for your situation, you will need to calculate how much product to apply to achieve the rate that was recommended in the foliar results. Learning how to calculate your fertilizer rate is important for the success of your crop. Please follow the examples below.<\/p>\n\n\n\n<div align=\"center\" role=\"math\" aria-label=\"Product weight in pounds per acre equals recommended nutrient rate in pounds per acre divided by percent nutrient in fertilizer in decimal form.\">\n  <p>\n    <strong>Product weight (lb.\/A)<\/strong> =\n    <span style=\"display:inline-block;vertical-align:middle;text-align:center\">\n      <span style=\"display:block;border-bottom:1px solid currentColor;padding:0 0.25em\">\n        Recommended nutrient rate (lb.\/A)\n      <\/span>\n      <span style=\"display:block;padding:0 0.25em\">\n        Percent nutrient in fertilizer (decimal form)\n      <\/span>\n    <\/span>\n  <\/p>\n<\/div>\n\n\n\n<p><strong>Equation 1. <\/strong>Equation showing how to calculate fertilizer product weight per acre by dividing the recommended nutrient rate by the percent nutrient contained in the fertilizer, expressed as a decimal.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Example A<\/strong><\/h4>\n\n\n\n<p>The foliar test recommends:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>190 lb.\/A phosphate<\/li>\n\n\n\n<li>Less than 50 lb.\/A nitrogen<\/li>\n<\/ul>\n\n\n\n<p>The suggested source is MAP 11-52-0<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The fertilizer contains 11% nitrogen<\/li>\n\n\n\n<li>The fertilizer contains 52% phosphate<\/li>\n<\/ul>\n\n\n\n<p><strong>Steps for Example A:<\/strong><\/p>\n\n\n\n<div align=\"center\" role=\"math\" aria-label=\"Three hundred sixty-five pounds per acre equals one hundred ninety divided by zero point five two.\">\n  <p>\n    <strong>365 (lb.\/A)<\/strong> =\n    <span style=\"display:inline-block;vertical-align:middle;text-align:center\">\n      <span style=\"display:block;border-bottom:1px solid currentColor;padding:0 0.25em\">\n        190\n      <\/span>\n      <span style=\"display:block;padding:0 0.25em\">\n        0.52\n      <\/span>\n    <\/span>\n  <\/p>\n<\/div>\n\n\n\n<p><strong>Equation 2.<\/strong> Example equation showing how 190 lb.\/A phosphate divided by the guaranteed fertilizer analysis rate of phosphate (0.52 or 52%) results in 365 lb.\/A of fertilizer product needed.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Determine how much product is needed to supply the phosphate recommendation.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Divide 190 by 0.52 to find the amount of product needed.<\/li>\n\n\n\n<li>You would need about 365 lb.\/A of product.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Determine how much nitrogen would also be applied.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Multiply 365 by 0.11 to find the nitrogen applied.<\/li>\n\n\n\n<li>This provides 40.2 lb.\/A nitrogen.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Compare the nutrient amounts to the recommendation.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Applying 365 lb.\/A of 11-52-0 would provide:\n<ul class=\"wp-block-list\">\n<li>190 lb.\/A phosphate<\/li>\n\n\n\n<li>40.2 lb.\/A nitrogen<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>This falls within the recommendation because the nitrogen rate is still below 50 lb.\/A.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<p>The foliar test recommendation may also include a suggested product application range. You, as the grower, choose the final rate within that range based on your management goals. Avoid applying more than recommended because excess fertilizer can waste money, increase nutrient leaching, and encourage excessive leaf growth instead of fruit production.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Example B<\/strong><\/h4>\n\n\n\n<p>The foliar test recommends applying:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>70 lb.\/A nitrogen<\/li>\n\n\n\n<li>180 lb.\/A phosphate<\/li>\n<\/ul>\n\n\n\n<p>The suggested fertilizer source is DAP 18-46-0.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The fertilizer contains 18% nitrogen<\/li>\n\n\n\n<li>The fertilizer contains 46% phosphate<\/li>\n<\/ul>\n\n\n\n<p><strong>Steps for Example B:<\/strong><\/p>\n\n\n\n<div align=\"center\" role=\"math\" aria-label=\"Three hundred eighty-nine pounds per acre equals seventy divided by zero point one eight.\">\n  <p>\n    <strong>389 (lb.\/A)<\/strong> =\n    <span style=\"display:inline-block;vertical-align:middle;text-align:center\">\n      <span style=\"display:block;border-bottom:1px solid currentColor;padding:0 0.25em\">\n        70\n      <\/span>\n      <span style=\"display:block;padding:0 0.25em\">\n        0.18\n      <\/span>\n    <\/span>\n  <\/p>\n<\/div>\n\n\n\n<p><strong>Equation 3.<\/strong> Example equation showing how 70 lb.\/A nitrogen divided by the guaranteed fertilizer analysis rate of nitrogen (0.18 or 18%) results in 389 lb.\/A of fertilizer product needed.<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Determine how much product is needed to supply the nitrogen recommendation.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Divide 70 by 0.18 to find the amount of product needed.<\/li>\n\n\n\n<li>You would need 389 lb.\/A of product.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Determine how much phosphate would also be applied.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Multiply 389 by 0.46 to find the phosphate applied.<\/li>\n\n\n\n<li>This provides about 179 lb.\/A phosphate.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Compare the nutrient amounts to the recommendation.<\/strong>\n<ul class=\"wp-block-list\">\n<li>Applying 389 lb.\/A of DAP 18-46-0 supplies:\n<ul class=\"wp-block-list\">\n<li>70 lb.\/A nitrogen<\/li>\n\n\n\n<li>179 lb.\/A phosphate<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>This meets the recommendation.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<p>After calculating the fertilizer needed for your field, calibrate your spreader to ensure the product is applied accurately. Calibration methods vary by spreader type and fertilizer product.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Ongoing Research<\/strong><\/h3>\n\n\n\n<p>Lily Calderwood and Alison King at the University of Maine are working together to study the nitrogen response in wild blueberry to determine the optimal time to collect foliar samples and when to fertilize. Lily Calderwood is also studying rates and timing of ammonium sulfate applications in addition to a baseline application of MAP. Thus far, her team has found that applications of fertilizer right before blueberry emergence are best and that wild blueberry yield increases as 20, 30, and 40 lb. N\/A are applied. For reference, 200 lb. of DAP per acre delivers 36 lb. of N\/A.<\/p>\n\n\n\n<p>For organic and fresh pack producers, an increase in weed pressure and split berries may concern you. In this case, we recommend, depending on your foliar sample, applying no more than 20 lb. N\/A. This will provide a smaller increase in yield while reducing the risk of crop loss from split berries.<\/p>\n\n\n\n<p>Each farm needs its own weed and nutrient management plan because different soil types and economic circumstances influence on-farm input decisions. Need help developing a nutrient management plan for your farm? Contact Dr. Lily Calderwood at <a href=\"mailto:lily.calderwood@maine.edu\">lily.calderwood@maine.edu<\/a>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>References<\/strong><\/h3>\n\n\n\n<p>Calderwood, L., Calder, B., Parks, J., &amp; Fanning, P. (2026). <em>Foliar calcium formulations and application timing on fruit firmness and retention in wild blueberry (Vaccinium angustifolium).<\/em> In <em>2026 UMaine Extension Wild Blueberry Annual Research Report<\/em>. University of Maine Cooperative Extension.<\/p>\n\n\n\n<p>Espinoza, N., Lessl, J., &amp; Rubio Ames, Z. (2025). High soil potassium levels do not increase leaf potassium concentration in rabbiteye or southern highbush blueberry. <em>HortScience, 60<\/em>(1), 152\u2013161. <a href=\"https:\/\/doi.org\/10.21273\/hortsci18251-24\">https:\/\/doi.org\/10.21273\/hortsci18251-24<\/a><\/p>\n\n\n\n<p>Santiago, J. P. (2011). <em>Determining optimum macro- and micronutrient leaf concentrations for lowbush blueberry (Vaccinium angustifolium Ait.) using the boundary line approach and quantile regression<\/em> (Master\u2019s thesis, University of Maine, Orono).Trevett, M. F. (1972). <em>Nutrition and growth of the lowbush blueberry.<\/em> Maine Agricultural Experiment Station Bulletin, University of Maine.<\/p>\n\n\n\n<hr>\n\n\n\n<p><em>Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.<\/em><\/p>\n\n\n\n<p>\u00a9 2026<\/p>\n\n\n\n<p><strong>Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit <a href=\"http:\/\/extension.umaine.edu\">extension.umaine.edu<\/a>.<\/strong><\/p>\n\n\n\n<p><em>University of Maine Cooperative Extension is an equal opportunity institution and provider committed to nondiscrimination. For more information, visit <a href=\"https:\/\/extension.umaine.edu\/nondiscrimination\">extension.umaine.edu\/nondiscrimination<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>By Lily Calderwood, Ph.D., wild blueberry specialist and associate professor of horticulture, University of Maine Cooperative Extension; Leala Machesney, Extension and research professional, University of Maine Cooperative Extension and Jordan Parks, wild blueberry research technician, University of Maine Cooperative Extension For information about UMaine Extension programs and resources, visit extension.umaine.edu.Find more of our publications and [&hellip;]<\/p>\n","protected":false},"author":206,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-34791","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Bulletin #2383, Fertilizing Wild Blueberry Fields - Cooperative Extension Publications - University of Maine Cooperative Extension<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/extension.umaine.edu\/publications\/2383e\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Bulletin #2383, Fertilizing Wild Blueberry Fields - Cooperative Extension Publications - University of Maine Cooperative Extension\" \/>\n<meta property=\"og:description\" content=\"By Lily Calderwood, Ph.D., wild blueberry specialist and associate professor of horticulture, University of Maine Cooperative Extension; Leala Machesney, Extension and research professional, University of Maine Cooperative Extension and Jordan Parks, wild blueberry research technician, University of Maine Cooperative Extension For information about UMaine Extension programs and resources, visit extension.umaine.edu.Find more of our publications and [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/extension.umaine.edu\/publications\/2383e\/\" \/>\n<meta property=\"og:site_name\" content=\"Cooperative Extension Publications\" \/>\n<meta property=\"article:modified_time\" content=\"2026-06-03T17:05:35+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-scaled.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1920\" \/>\n\t<meta property=\"og:image:height\" content=\"2560\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"14 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/\",\"url\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/\",\"name\":\"Bulletin #2383, Fertilizing Wild Blueberry Fields - Cooperative Extension Publications - University of Maine Cooperative Extension\",\"isPartOf\":{\"@id\":\"https:\/\/extension.umaine.edu\/publications\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/#primaryimage\"},\"image\":{\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/#primaryimage\"},\"thumbnailUrl\":\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-768x1024.jpg\",\"datePublished\":\"2026-06-02T23:57:02+00:00\",\"dateModified\":\"2026-06-03T17:05:35+00:00\",\"breadcrumb\":{\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/extension.umaine.edu\/publications\/2383e\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/#primaryimage\",\"url\":\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-scaled.jpg\",\"contentUrl\":\"https:\/\/extension.umaine.edu\/publications\/wp-content\/uploads\/sites\/52\/2026\/06\/2383-tip-dieback-scaled.jpg\",\"width\":1920,\"height\":2560,\"caption\":\"Figure 1. An image showing tip-dieback at the top of a stem. The top leaf shrivels, turns brown, and dies at the end of June or beginning of July. This indicates that the stem is now putting energy into developing branches and buds instead of vegetative growth. Foliar samples should be taken at this time. Photo credit: Leala Machesney.\"},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/extension.umaine.edu\/publications\/2383e\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/extension.umaine.edu\/publications\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Bulletin #2383, Fertilizing Wild Blueberry Fields\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/extension.umaine.edu\/publications\/#website\",\"url\":\"https:\/\/extension.umaine.edu\/publications\/\",\"name\":\"Cooperative Extension Publications\",\"description\":\"Information you can use. 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