Fertilizing Plum Trees

Fertilizing is an excellent way to replenish the nutrients in your soil, especially nitrogen. Nitrogen encourages green vegetative growth, which is exactly what you want to promote before your plum tree reaches its fruit-bearing years.

Always test your soil prior to applying any fertilizers. Different soils can have varying amounts of native elements needed to support plum tree growth and development. If you discover your soil lacks any necessary nutrients (nitrogen, phosphates, potash, etc.), be sure to choose a fertilizer that supplements the soil’s nutrient deficiency.

Get to know your soil and discover the importance of soil testing prior to making any changes.

NOTE: This is part 6 in a series of 11 articles. For a complete background on how to grow plum trees, we recommend starting from the beginning.

Fertilizing New Trees

Fertilizing Established Trees

About Fertilizers

Fertilizers – both synthetic and organic (naturally derived) – are soil amendments labeled with a “guaranteed analysis” of nutrients like Nitrogen (N), Phosphate (P), and Potash (K).
Alternately, there are organic soil amendments, like compost and aged/rotted manure. They are used like fertilizers, but they are not technically fertilizers. You can make your own organic soil amendments, like compost, out of food or garden scraps, or even get compost, manure, and other organic soil amendments from a trusted local source. While these help add nutrients to the soil to support your plum trees, they will not have a “guaranteed analysis” value.
In general, plum trees thrive when macronutrients like Nitrogen (N), Phosphorous (P), and Potassium (K) are present. Nitrogen helps encourage vegetative growth (leaves and branches). Phosphorus encourages root and blossom development. Potassium/Potash is responsible for the efficacy of the plum tree’s natural disease-resistance and systems supporting its overall health, kind of like an immune system. A water-soluble fertilizer that is specifically formulated for use on young plum trees provides the nutrients these trees take in during their initial years in the ground as they become established.

Take care not to over-fertilize, or you may produce a tree that is unbalanced, which can affect fruit production and leave the tree susceptible to pests and disease.

Macronutrients

Nitrogen, phosphorus/phosphates, and potassium/potash are the “big” macronutrients plum trees need to grow normally. They are present in healthy soil, but may be added when soil is deficient. Nitrogen is the nutrient most used by growing plum trees; it moves throughout the soil, is leached off by normal growth and must be replaced by synthetic or organic compounds. The main source of nitrogen is decaying organic matter. Signs of macronutrient deficiency in plum trees include reddish or pale colored leaves, narrow or shrunken leaves and dead spots on leaves.

Micronutrients

Plum trees also need micronutrients in the soil, which help make the macronutrients available to the tree. For example, molybdenum helps fix nitrogen to the soil. Copper and zinc prevent color mottling and misshapen leaves. Calcium is another essential micronutrient that plum trees thrive on that improves leaf and fruit quality. The easiest way to add micronutrients is by adding aged compost or a good, balanced fruit tree fertilizer that states micronutrients are part of the formula.

When to Fertilize Plum Trees

In nutrient-rich soil, you can withhold using fertilizers until your plum trees begin bearing fruit (average: 2-4 years after planting). If your new plum trees don’t put on several inches of new green growth during the growing season, consider fertilizing starting the following spring.
Typically for plum trees, you can start fertilizing after bud break, but by no means any later than July. For any specific fertilizer application instructions, always refer to the information printed on your product’s label. Be mindful that local advisories on fertilizing may be in effect during certain times of year. For the sake of your local environment, please adhere to these restrictions.
Many fruit trees require more nitrogen after they start bearing fruit. Each year, test the soil to see what it needs, and if the nitrogen levels appear low, then apply a low-nitrogen fertilizer in small amounts a couple of weeks before bud break in early spring. Mulch your trees and keep weeds at bay, since weeds will compete with your plum trees for nutrients.

To prevent the chance of injury as the growing season winds down, do not fertilize past July 1st.