This is our fertilizer program for pome fruits - apples, pears, mayhaw, loquat, crabapples, and quince. We recommend reading our page Fertilizing Fruit Trees, which discusses some general and useful information about fruit nutrition.
Pome fruits require potassium, magnesium, calcium and a bit of boron. Pome fruits do not require a great deal of nitrogen fertilizer. In fact, excess nitrogen can:
- Favor vegetative growth over fruit production
- Negatively affect the quality of the fruits
- Lead to disease issues, such as fire blight
Pome fruits require some observation before the decision is made to provide nitrogen. If the shoots on your trees grew at least 8" in the previous year, the tree does not require supplemental nitrogen. If the shoots grew less than 8" the previous year, apply 1/10 lb of nitrogen per inch of trunk diameter, measured 12" above the grade. If your trees require nitrogen:
- Using a flexible tape measure (seamstresses tape), measure the circumference of the tree 12" above grade.
- Divide the result by 3 (it is actually 3.1415 or pi, but 3 is close enough). The result is the approximate diameter (caliper).
- Multiply the diameter x 1/10. The result is the number of pounds of nitrogen the deficient tree requires.
For example, if the circumference of the tree is 6", the diameter is approximately 2". You will need 2/10# or 0.2# of nitrogen. To determine how much fertilizer to apply by weight, divide the required pounds of nitrogen by the percent of nitrogen in your slow release organic fertilizer. The nitrogen content is indicated by the first number in the three digit code on the bag (N-P-K).
For example, if your tree requires 0.2 lb of nitrogen, and your SROF is 4-4-3, you will apply approximately 5 pounds of fertilizer. If you are using an SROF with a formula of 6-2-4, you will apply 3.33 pounds of fertilizer (round to 3.5 for simplicity).
4-4-3: .2 / .04 = 5.0#
6-2-4: .2 / .06 = 3.5#
For new trees, do not fertilize at planting. Wait until a strong flush of growth indicates that newly formed feeder roots are established (3 - 4 months after planting). Nitrogen applied with a balanced slow release organic fertilizer in the first year of planting will stimulate vegetative growth that can be selectively pruned the following dormant season when the tree is established.
For established trees, apply in (February at bud break). In my experience, it is seldom necessary to apply nitrogen fertilizer after the first year in the ground. With proper compost application and mulching, the shoots will meet or exceed 8" of annual growth.
Potassium (K) and magnesium (Mg)
Potassium and magnesium can be supplied several ways, but these are the simplest:
Option 1 – Sul-Po-Mag
Apply ½ lb of Sul-Po-Mag per inch of trunk diameter, not to exceed 2.5 lb per tree per year. Sul-Po-Mag has a soil life of approximately (6) months. One application in February will last the growing season.
Option 2 – Greensand & Epsom salts
Apply 3 lb of greensand and ½ lb of Epsom salts per tree per year. Greensand is not as readily available to the tree. It may not be bio-available until the second year after application. However, one application will last (3) years. Epsom salts do not accumulate in the soil, and do not have a long soil life. You can apply the Epsom salts each month from February through August to provide magnesium.
If you decide on Option 2, you must compensate for the slow availability of the greensand. You can do this with the shorter-lived Sul-Po-Mag. When you make your first application of greensand, apply Sul-Po-Mag at the rate described in Option 1 at the same time. The Sul-Po-Mag will provide the required nutrients for the first year. The greensand will kick in the following year. If you apply Sul-Po-Mag for this purpose, you will not need to apply Epsom salts until the second year.
Calcium should be provided in a form that does not raise soil pH. Gypsum is a good source, and has other benefits to the soil, such as displacing sodium and increasing permeability. Apply 10# of gypsum per tree.
Apply gypsum once a year. It can be applied at anytime, but it is easiest to apply it in February when you are applying other nutrients, and before you apply compost and mulch for the year.
Boron can be supplied using 20 Mule Team Borax available in the laundry section. Apply 1/4 cup per tree every (3) years. Do NOT over-apply boron. It is a necessary nutrient, but excessive amounts can be toxic to plants.
How to apply
For newly planted trees, apply supplements in a 3' circular band around the tree, starting 8"-12" from the trunk. For established trees, broadcast supplements in a 6' - 8' circular band around the tree, starting 12" from the tree.
It can be difficult to evenly spread the small amount of borax. You can dissolve it in water and distribute it with a watering can. An easy way to get even distribution is to mix all of the supplements in a bucket, including the borax, making sure they are very well blended, and then broadcast them at one time.
It is not necessary to cultivate the supplements into the soil. Gypsum can be scratched into the top 2" using the times of an iron rake. Top your application off with 1" - 2" of compost and apply mulch.
Annual schedule summary:
Newly planted trees - apply greensand, gypsum, and boron at planting time. Once strong new growth indicates that feeder roots are becoming established (3 - 4 months after planting), apply a balanced slow release organic fertilizer as described above and begin monthly applications of Epsom salts.
Established trees - If you are using Sul-Po-Mag, make the application in February. If you are using greensand and Epsom salts, apply the greensand once every 3 years and apply Epsom salts once a month February through August. Apply gypsum once each year. Apply borax once every three years. Apply nitrogen only if growth is lagging.