A plum tree covered in blossoms but lacking fruit signals a hidden issue in its development, environment, or care routine. Understanding the potential causes, from biological requirements to cultural practices, is the first step toward correcting the problem and ensuring a future bounty of plums.
Age and Pollination Requirements
A plum tree’s age is the simplest initial factor to consider. Newly planted trees require time to reach reproductive maturity, typically bearing fruit between three and six years after planting, depending on the variety and rootstock. The tree must first develop specialized, short branches called fruiting spurs, which form on older wood over a few seasons.
The variety’s pollination requirement is another fundamental check, as many plums are not self-fertile and require a partner tree. Self-sterile varieties must receive pollen from a different, compatible plum variety that flowers simultaneously. Even self-fertile varieties, such as ‘Methley’ or ‘Santa Rosa,’ often produce a heavier crop when a cross-pollinator is nearby.
For successful cross-pollination, the compatible partner tree must be located within 100 to 500 feet to allow bees to efficiently transfer pollen. It is also important to note that most European plums (Prunus domestica) and Japanese plums (Prunus salicina) are unable to cross-pollinate one another. Therefore, the partner variety must belong to the same species group.
Environmental and Weather Factors
The local climate must satisfy the tree’s biological needs during winter dormancy. Plum trees require a specific number of cold hours, known as chilling hours (time spent between 32°F and 45°F). This cold period is necessary for flower buds to properly break dormancy and develop into healthy spring blossoms.
Insufficient chilling hours, common in warmer winters, leads to weak, uneven bloom, delayed leafing, and poor fruit set. The chilling requirement varies widely: European plums often need 800 to 1200 hours, while some Japanese varieties need 300 to 900 hours. If the requirement is not met, the tree may produce sterile flowers or drop them prematurely.
Late spring frost is another common environmental culprit, as plums are one of the earliest fruit trees to bloom. Once flowers or newly set fruitlets emerge, they become highly sensitive to freezing temperatures. A temperature of 28°F can kill 10% of open blossoms, and 24°F can cause a 90% loss of the potential crop by destroying the reproductive structures inside the flower.
Extreme weather during the brief blossoming period also hinders fruit set by interfering with pollinating insects. Extended periods of heavy rain, strong wind, or cold temperatures prevent bees from flying, interrupting pollen transfer. Additionally, excessive heat or drought stress during the fruit-setting stage may cause the tree to self-abort the fruitlets as a survival mechanism.
Cultural Care Mistakes
Pruning and fertilization directly impact the plum tree’s capacity to produce fruit. Plums bear their harvest on fruiting spurs, which are maintained by careful pruning. Cutting back too much older, spur-bearing wood, or removing new wood that would develop into future spurs, effectively eliminates the crop.
Plums should only be pruned in the early spring or mid-summer to minimize the risk of infection from silver leaf disease. Proper pruning aims to open the tree’s center to sunlight and air circulation. However, excessive removal of wood is a frequent mistake that can take years to correct.
An imbalance in soil nutrients, particularly an overabundance of nitrogen, is another common cultural error. Nitrogen promotes strong vegetative growth, resulting in lush leaves and vigorous new shoots. Too much nitrogen directs the tree’s energy into leafy growth at the expense of flower bud formation.
To encourage fruit production, nitrogen application must be moderated, and the need for other macronutrients should be considered. Phosphorus is necessary for healthy flower and root development. Potassium plays a role in overall fruit quality and disease defense. A soil test can help determine if a lack of phosphorus or potassium contributes to poor fruit set.
Pest and Disease Impact
Pests and diseases can target the reproductive parts of the plum tree, causing blossoms or fruitlets to fail before maturity. Brown rot, caused by the fungus Monilinia fructicola, attacks flowers during the bloom period. This infection, known as blossom blight, causes blossoms to turn brown and shrivel, preventing fruit set.
Insect pests also destroy the crop in its earliest stages. The Plum Curculio, a small weevil, attacks newly formed fruitlets. The female chews a crescent-shaped scar into the skin to lay an egg, and this damage often causes the fruit to drop while still small.
Infestations by other insects, such as the Plum Sawfly, similarly lead to the premature dropping of young fruit. When pests or diseases target the flowers or fruitlets, a severe outbreak can result in a near-total loss of the year’s harvest, even if the tree appears generally healthy.