MSU Extension

Nutrient management in chestnut trees is unique among perennial tree crops. A complete fertilization program based on soil testing, annual leaf analysis and observation of tree growth will maximize the establishment and development of chestnut trees.

Many soils in Michigan provide nutrients in sufficient levels for chestnut production. However, before planting, Michigan State University Extension recommends growers do a soil test. A soil test provides you with valuable information on soil pH, texture and nutrient status. Chestnut trees require well-drained soils and a pH of 5.0-6.5. Even though optimum nutrient levels for phosphorus, potassium, calcium and magnesium are not known for chestnuts, a soil test can provide you with information to base your nutrient and sulfur or lime addition decisions. Scroll down to the bottom of this article to read more about soil testing.

Nitrogen management for chestnuts

Nitrogen is an essential nutrient and plays an essential role in many plant functions. Fertilizer application is a necessary part of your orchard maintenance as the nitrogen status of a tree can have a profound effect on health and vigor. When considering how much nitrogen to use, more is not necessarily better. Excessive nitrogen fertilization will over-invigorate vegetative growth on bearing trees, which will result in reduced flower bud formation and reduced fruit yield. It is important to provide enough nitrogen to maintain healthy nutritional status, but to not oversupply nitrogen.

Fertilizer use during the first year is not recommended and may cause damage to roots. Fertilizer recommendations for years two through five are based on better-studied systems, including apples. After the fifth year, tree vigor and health as well as trunk diameter are used to determine fertilizer rates.

Nitrogen recommendations, 0-5 years

Using this table, you can select the fertilizer of your choice based on availability and specific needs. Note the difference between actual nitrogen, “Amount of nitrogen per tree,” and product amount as indicated in the “Urea,” “Ammonium Nitrate” and “Ammonium Sulfate” columns.

Annual nitrogen recommendations for chestnut trees from planting through year five.

These recommendations are based on standard fruit and nut tree nutrient management from Europe. A given site may require more or less depending on soil and leaf analysis.

Visual observation of leaf color can also be a useful indicator of tree health. Leaf yellowing may be an indicator that the soil pH is too high at those locations which prohibits the tree from efficiently utilizing the macro and micronutrients you have made available. Growers should be evaluating and adjusting pH via soil testing and visual observation.

Nitrogen recommendations, older than 5 years

Fertilizer rates for bearing chestnut trees are determined by tree size and vigor. The diameter of the trunk is multiplied by the nitrogen rate based on the average length of last year’s terminal branch growth.

• Low vigor: If tree growth is considered low (under 8 inches per year) then a multiplier rate of 1/6 pound (2.7 ounces) nitrogen per inch of trunk diameter is used.
• Normal vigor: If tree growth is considered normal (8 to 12 inches per year) then a multiplier rate of 1/8 pound (2 ounces) nitrogen per inch of trunk diameter is used.
• Excessive vigor: If growth is more vigorous (greater than 12 inches on average) then a multiplier rate of 1/10 pound (1.6 ounces) nitrogen per inch of trunk diameter

Note: Regardless of the outcome of the nitrogen calculation above, no more than 1 pound of actual nitrogen should be applied per tree annually.

Example:

• 5-inch trunk diameter
• 5-inch average terminal branch length last year
• Fertilizer of choice – Ammonium sulfate (21-0-0)

How much ammonium sulfate do you have to apply to get the correct amount of nitrogen?

Answer: Your average terminal growth last year was 5 inches, indicating a low vigor, which means you would need 1/6 pound (2.7 ounces) nitrogen per inch of trunk diameter.

5 inch trunk diameter x 2.7 ounces N = 13.5 ounces actual N needed per tree

Ammonium sulfate is only 21 percent nitrogen, so to determine the rate of product needed, use the following formula:

Actual nitrogen (oz.) ÷ by nitrogen in product (%) = product needed (oz.)

13.5 ounces actual N ÷ 0.21 percent N in ammonium sulfate = 64.3 ounces of ammonium sulfate per tree

Annual nitrogen recommendations for bearing chestnut trees six years or older.

*Based on tree uptake, nitrogen applications should never exceed 1 pound actual nitrogen per tree annually.

Fertilizer timing and placement

There are several standard ways available to apply nitrogen and other nutrients to your trees in your orchard and probably dozens of less than standard ways that work. The guidelines below are based on soil application of the nitrogen. While some people may apply it to the leaves, there is no precedent for foliar applications on chestnut. 



Timing of nitrogen fertilizer applications to the soil surface influences the type of response trees are likely to exhibit. With most tree crops, early season growth potential and strength of flower buds are largely determined by the nitrogen reserves that the buds contain when growth begins that season. This is a standard statement used for most fruit trees. However, most fruit trees flower in spring. Chestnuts flower in very late spring or early summer. We may be able to have some influence with our spring nitrogen application on the strength of the flower bud with spring application of nitrogen.

With most tree crops, nitrogen fertilizers applied during the dormant season as soon as the snow clears will stimulate vegetative growth and generally do not influence the nitrogen status or strength of current season flower buds or fruit set. This may be true for chestnut too.


Applications during the summer, particularly after current season shoot growth has been completed, are more likely to result in improved nitrogen status of the buds for the next season. However, applications of nitrogen late in the summer may delay or reduce fruit development, increase the pre-harvest fruit drop, delay maturation of buds and woody tissues or stimulate late season growth, thus increasing susceptibility of woody tissues and buds to cold injury. In regions where cold injury is of concern, summer applications of nitrogen must be carefully managed to ensure the tree properly shuts down in preparation for winter. Fall applications of nitrogen may delay hardening of buds and woody tissues and increase the potential for desiccation during the winter, particularly if made before trees have become completely dormant.

For most efficient use, nitrogen fertilizers should be spread over the area where the herbicide treatment eliminated the weeds (weed-free zone) or along the cultivated tree-row strips where the majority of the active tree roots are located. Application to weeds or grasses will act to fertilize the weeds and the tree roots will get the leftovers. For this reason, broadcasting over the entire orchard floor is less efficient, requires considerably greater rates of application and is more likely to benefit ground covers than the trees.



Soil testing

Soil testing is an important diagnostic tool in evaluating nutrient imbalances and understanding plant growth problems. Soil test results help growers adjust fertilizer application to provide nutrients that are lacking in the trees. Also, soil testing helps growers maintain soil pH within an optimum range (5.5-6.5 for chestnuts), which keeps nutrients available for plant uptake.

The soil test section is usually placed with the fertilizer section of a report like this, but we place it here to inform you that it should be used before you even plant your orchard. The soil test report includes soil pH, lime index, available phosphorus, potassium, calcium and magnesium, liming and fertilizer recommendations based on the crop to be grown and soil test results. MSU recommendations are given in “pound of nutrients needed,” not pounds of commercial fertilizer to be applied. To learn more about soil tests or to send in a sample, visit the MSU Soil and Plant Nutrient Laboratory website.