How and if you fertilize and water a plum tree will depend on several factors including: soil type, soil fertility, weather conditions and location. These trees grow satisfactorily in moderately fertile soils without fertilizer. However, fertilizer is needed in soils of low fertility or where competition from other plants is heavy.
Best Growing Conditions
Sun - The best and most fruits will be produced when trees are growing in full sun. However, trees that receive a little shade during the hottest part of summer days will still produce good crops of fruit.
Soil Type Preferred - Plum trees grow and produce the best fruit in well-drained but moist fertile soil that is rich in organic matter, but tolerate a wide range of soils as long as water and nutrients are not limiting and soil pH is adequate. Plum tree roots will not tolerate soils where water remains on or near the surface for more than one hour after a heavy rain. They are tolerant of heavy clay soils if drainage is good. In soil with low fertility or compact clay it'll be worth your time to mix in some organic compost to the native soil. They like the soil to hold a good supply of water, especially when the fruits are developing in summer, but not so much water that the soil stays constantly soggy or wet.
Soil pH Preferred - Plum trees do best in a slightly acidic to neutral soil, somewhere between 6.0 and 6.5 on the pH scale. Whenever growing plants that prefer a specific pH it's a good idea to test the soil. Testing kits are available at most local nursery and garden centers or you can buy soil test kits online here. Your local Extension Service might provide soil testing services as well. Depending on the results of the soil test, you can add lime to raise the pH or soil sulfur to lower the pH (make more acid).
Type Of Fertilizer
Plum trees planted in very fertile soil may not require fertilization until they've used up many of the nutrients. The best way to decide on wether or not to fertilize is to observe the tree itself. If growth is stunted and you don't see at least 1 foot of growth per year, or what otherwise should be dark green leaves have become light green, this indicates a need for fertilization. If the leaves are light green the tree cannot photosynthesize effectively for the best fruit production. Fertilizer will darken the foliage over time and help to stimulate good fruit production.
Trees can be fed with organic plant foods or inorganic fertilizers, such as 10-10-10. Avoid the use of fertilizers that have a high nitrogen content (the first number in fertilizer). When feeding plants that will put produce on the kitchen table, I always go with organic. Organic plant foods and composts are usually non-burning and will not have chemicals or other inorganic substances in them. The type of fertilizer you choose to use is up to you.
Nitrogen Consideration - Although nitrogen is a necessary element for basic plant growth, plum trees, and most other fruit trees, react dramatically if there is too much nitrogen (the first number in fertilizer). The nitrogen redirects energy from fruit production to foliage and shoots. If there's too much nitrogen in the soil fruits might prematurely fall to the ground before they are fully developed.
When To Fertilize A Plum Tree
Feed plum trees just after new leaves have emerged in late winter or early spring. The surge of nutrients at the soil level will spur the tree to grow with vigor and produce good fruit.
Fertilizing Newly Plum Trees...
When planting a plum tree during the dormant season, when trees have no leaves, do not apply fertilizer. Wait to fertilize until new growth begins to emerge in spring. Container-grown trees can be fertilized at planting time when planted during the spring and summer, however avoid fertilization two months prior to the typical first frost date in your area. Late fertilization can stimulate new tender growth that can be damaged, and damage the entire tree, from an early freeze.
Fertilizing Established Plum Trees...
If you choose to go with an inorganic fertilizer, a basic 10-10-10 or 8-8-8 fertilizer works well. The size of the tree will determine the amount of fertilizer you'll apply. For each 1-inch of diameter of a tree apply 1 pound of fertilizer. Use a ruler to measure the diameter of the trunk at 1 foot above the ground. Depending on the size of the canopy, you can hand sprinkle or use a hand spreader to broadcast the fertilizer around the perimeter of the canopy, which is where most of your mature tree's feeder roots will be.
Alternatively you can use a non-burning organic type fertilizer, or you can use a layer of organic compost as mulch (composted cow manure, etc), so that less chemicals are added to the soil that could end up in your fruit, and eventually in your body.
Watering Plum Trees
The frequency and the amount of water a plum tree will need depends to a large extent on the soil and the age of the tree. As a rule of thumb, 1 inch of water per week from rain or irrigation is adequate. Just keep in mind that soil should be moist but not constantly soggy. Plum trees, like most other fruit trees, do not like constantly wet feet! If water stands more than an hour on the surafce of the soil steps need to be taken to improve drainage.
Irrigation of young trees is especially important during the first season or two, but be careful not to overwater.
Mature plum trees are quite drought tolerant but will need sufficient water during the fruiting period to produce a good yield of healthy fruit.
- Always keep a sufficient layer of much around your trees to control competition from weeds and help retain moisture.
- Excessive nitrogen can cause too much foliage growth.
- Yellowing and dropping of leaves may indicate drought and the need for supplemental irrigation or fertilization.