Is your plum tree not producing fruit? Or are you wondering why there are no plums on your tree?
You can usually tell if your plum tree will yield ripened plums by examining the flowers immediately after the petals fall off. The ovary (which will become the fruit) is located at the base where the petals were. It should be swollen and enlarged. If it isn’t, there was a problem with fruit set which could be due to poor pollination, unfavorable weather, insect pests, or poor health of the tree.
Another plum tree fruit problem could be if the tree did not flower at all. It could be because of inclement weather, insufficient chilling hours, or the tree was too young. If your tree flowered, then started developing small fruit, but the fruit aborted, the problem could be pests or plum tree diseases.
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Here is an updated list of plum tree problems that may arise:
Is the tree mature enough?
Has your flowering plum tree been in the ground long enough to be well established? Plum trees typically begin to bear fruit when they are three to six years of age. Fruit develops earlier in some varieties and you even see baby plums begin to appear earlier in age. The fruit will continue to get bigger and bigger until it reaches maturity.
If plums form and begin to enlarge but then drop to the ground before they mature, it could be because the flowers were not pollinated. If the aborted plums lack a seed (stone) this was the problem.
Many plum trees are self-incompatible; that is, they require cross-pollination from a different variety of plum tree before they will set fruit. Even the plum varieties considered self fertile tend to produce more fruit when they are cross-pollinated. For a plum tree to produce at its best, there must be another variety of plum tree blooming at the same time within 50 feet or less, and some willing pollinators to do the transferring.
The main pollinators for plum trees are insects, especially bees, and particularly honey bees. If there are no bees around, there will be little cross pollination. You can encourage pollinating insects by growing nectar plants and avoiding the use of insecticides.
If the weather is rainy or cloudy or exceptionally windy for several days during the bloom period, bees will be less active, and this can diminish pollination and result in fewer plums.
There are two main groups of cultivated plum trees: (1) Japanese plums (Prunus salicina) and their hybrids and cultivars; and (2) European plums (P. domestica) and their hybrids and cultivars. Both types bloom in early spring and the plums produced ripen in summer. Both types are self-incompatible or partially self-incompatible; that is, their flowers require cross-pollination from a different variety for maximum fruit production.
European and Japanese varieties cannot cross pollinate each other. In general, any two varieties from the same group can pollinate each other as long as they are blooming at the same time.
Plum trees require a specific duration of cooler temperatures in winter, (called chilling hours) before they will bloom the following spring. Chilling hours are the total number of hours that the temperature is between 32°F and 45°F. (The hours do not need to be consecutive.)
If a plum tree’s chilling hour requirement is not met, the tree may not even produce flowers, or it may bloom too early and the blossoms get destroyed by frost. Most Japanese plum varieties need 500 to 900 chilling hours. European plum varieties often require 700 to 1,000 chill hours, but there are varieties adapted to warmer climates.
Plum trees with low chilling requirements of 150-300 hours, suitable for southern locations, include Santa Rosa Plum, Burgundy, Mariposa, Methley Plum, Shiro, and Satsuma. Chilling requirements are usually provided on the nursery’s label, and do not equate directly with USDA hardiness zones. Use this interactive source to get the average chilling hours for your location: http://agroclimate.org/tools/chill-hours-calculator/
Exceptionally high winds or drenching rains in spring can damage buds or flowers, causing them to fall off and not produce fruit. Flower buds can be killed by an extremely cold winter. Choose plum trees adapted for your climate zone.
Unusually extreme cold or frost during or immediately before the blossoms open can cause them to wither and fall off. If this happens, there will be no fruit. Covering the tree with a lightweight fabric (such as Reemay®) can protect the blossoms from frost. To protect from extreme cold, you will need to cover the tree with something more substantial (like a blanket) and include a heat source such as an electric light bulb.
Plum curculio infestation?
Plum curculio (Conotrachelus nenuphar), is a small beetle that
lays eggs within developing fruits, causing them to drop prematurely. The skin of infected fruit will have small
crescent-shaped blemishes, and the plum will be hard and misshapen. Look closely, and tiny beetle larvae can be seen near
If you have a plum curculio infestation, eggs or larvae will be developing within fruit lying on the ground. Clean it up. If you had infested plum trees last year, cultivate the soil around them to destroy larvae that may be overwintering in the ground.
If you have only a few infested trees, plum curculios can be physically shaken out of them. Early in the day, when the beetles are sluggish, spread paper or cloth underneath the trees, and shake the trees vigorously. The adult beetles will fall out of the tree onto the cloth. Dump them into a pail of soapy water.
If you have a severe infestation of plum curculio beetles you can apply carbaryl (Sevin ® spray), phosmet, malathion, pyrethrins, or the organic fungus Beauvaria bassiana. Delay application of any pesticide until after flower petals drop to avoid harming beneficial pollinating insects. Reapply pesticides two more times, at 10–14 day intervals, but not right before harvest. Always follow label instructions.
Other insect pests?
Plum sawflies, mites, scale insects, aphids, various moths, and other insect pests can infect plum trees and fruits, reducing or eliminating a crop. Many of these insect pests can be controlled by spraying the trees with dormant oil or neem oil in late winter. Dormant oil and neem oil are accepted organic pesticides. They work by smothering insects and their eggs. As always, follow manufacturer’s directions.
If the blossoms, fruit, and/or twigs and branches of your plum tree are covered with a dark brown slime, it is probably infected with the fungus known as brown rot (Monilinia fructicola). Brown rot will cause the plums to become soft and shriveled, and eventually drop off the tree. Remove and destroy infected fruit in late summer or fall. Remove and destroy diseased branches in winter. It could also mean infected leaves which will also need to be picked off.
Fungi like it humid. Keep your plum trees pruned to maintain good air circulation. When watering the tree, water the soil, not the foliage. If brown rot has traveled down to the soil level, you might need to talk to an expert.
If brown rot continues to be a problem, you may have to resort to chemical fungicides. Apply a copper based fungicide in early spring while the trees are still in their pink bud stage (before blossoms open) and again three weeks prior to plum harvest. Always follow label directions.
Plum trees should get at least eight hours of full sun a day. Do not plant your plum trees where they will be shaded or get root competition from other trees.
Plum trees should get about an inch of water each week from rain or irrigation; otherwise they may drop blossoms and/or abort fruit. If rainfall is insufficient, water enough to soak several inches into the soil once a week.
Fertilize fruit trees with a balanced formula like 10-10-10 or one that is higher in phosphorus (the P in N-P-K), as this is the element that most encourages blooming and fruiting. Our Bulk 360 day slow release fertilizer will work well! Bone meal is a great way to augment a plum tree’s supply of phosphorus.
Prune your plum trees to create a strong scaffold, eliminate crossed branches, and keep the tree at a manageable size. Cut out suckers that sprout from the base of the tree and watersprouts that shoot up from branches. Prune in winter when the tree is dormant but before buds have formed. Learn more about basic pruning for trees and shrubs.
Maintain an area free of weeds and grass for about three feet around the tree. A soil amendment such as our Fruit Tree Planting Mix will help poor soils come back to life!
Excess Nitrogen Fertilizer?
Nitrogen fertilizer promotes leafy, vegetative growth and can diminish flowering if applied in excess. Do not over-fertilize and always follow label directions when fertilizing your plum trees. All About Fertilizers here.
If a plum tree bears heavily one year, it may produce fewer plums or none at all the following year. Thinning the developing plums while still small (about the size of a marble) in early summer to one fruit every 4-6 inches along the branches will result in fewer fruits ripening, and may lessen the effects of alternate bearing. Remove the smallest fruits and keep the larger ones. Usually, there isn’t much we can do to eliminate alternate bearing.
Other plum tree diseases that may be affecting your tree
Your tree may show signs of black knot or powdery mildew. These are two very common plum tree diseases that affect plum trees and other fruit trees across the United States.
In black knot, abnormal growth on bark or wood near the twigs and branches swells to produce large cankers. This disease could be fatal and infest other trees in the area as it can overwinter and come back year after year if not taken care of.
Powdery mildew is a common disease among many fruit trees that will produce a white substance on infected leaves and branches. The leaves will curl upwards. You may see a leaf spot appear on the plum trees and others stone fruits.
Fungicides can offer protection from both of these plum tree problems. It is important to shield your trees from diseases like this to avoid infestation because it could devastate your fruit trees and could stunt growth at the expense of the fruit.
Plum trees are an excellent choice of fruiting tree for many gardeners! They can grow in a variety of climates and are cold hardy to some degree. Makes a good fruit tree for the Midwest states as well with harsh winters.
Happy planting! Please contact us with any questions you may have. Our experts will help with any issues regarding why your plum tree is not producing fruit. We are here to help!
Check out our Plum Grow Guide for more information on planting, growing, and harvesting these delicious fruits!