Plum trees, like many fruit bearers, rely on the transfer of pollen for successful fruit development, a process generally carried out by bees and other insects. For a gardener, knowing whether a plum variety can pollinate itself is important for planning an orchard and ensuring a bountiful harvest. The capacity for a plum tree to produce fruit without a partner depends entirely on its specific genetic makeup. Determining a tree’s self-pollinating status dictates whether a single tree can be planted or if a second, compatible variety is needed.
Understanding Self-Fertility in Plums
The term self-fertility describes a plum tree’s ability to set fruit using its own pollen, meaning it does not require a different variety nearby. Conversely, a self-unfruitful tree cannot set a satisfactory crop with its own pollen and must receive pollen from a genetically distinct partner. Many stone fruits, such as most peaches and tart cherries, are reliably self-fruitful, but plums present a wider variation in their requirements.
While some plum varieties are genuinely self-fertile, the overarching rule is that production is often enhanced by cross-pollination. Even trees considered self-fertile will typically yield a heavier crop of larger fruit when planted near a compatible partner. A tree that is only partially self-fertile may produce a small amount of fruit when isolated, but requires a cross-pollinator to ensure consistent yields. For the home gardener aiming for reliable fruit, understanding the specific needs of the cultivar is the first step toward a successful harvest.
Pollination Needs of Major Plum Varieties
Plums are broadly categorized into two major groups: European and Japanese. Their origins heavily influence their pollination requirements, and these two groups are generally not genetically compatible. Therefore, selecting a partner tree requires matching both the general type and the specific variety.
European Plums
European plums (Prunus domestica), which include varieties like ‘Stanley’ and Damson plums, are generally more likely to be self-fertile. ‘Stanley’ and ‘Damson’ are commonly listed as self-fertile, although their fruit set improves considerably with a cross-pollinator. European plums tend to bloom later than their Japanese counterparts. Many European cultivars can successfully pollinate each other as their bloom times frequently overlap.
Japanese Plums
Japanese plums (Prunus salicina) and their hybrids are almost universally self-unfruitful and must have a compatible partner variety to produce fruit. Varieties such as ‘Burbank’ and ‘Ozark Premier’ will not set a satisfactory crop with their own pollen. Growers often rely on “universal” pollinators like ‘Santa Rosa’ or ‘Shiro,’ due to their long bloom periods and high pollen viability. Hybrid plums also typically require a specific Japanese plum pollinator for fruit set.
Choosing the Right Pollinator Partner
When cross-pollination is required, a successful pairing relies on two main biological factors: genetic compatibility and synchronized bloom time. The partner tree must be a genetically different variety within the same species group. This means a Japanese plum needs a different Japanese plum, and a European plum needs a different European plum. Planting incompatible types, such as pairing a European with a Japanese variety, will not result in fruit.
Bloom Time Overlap
The most important factor for effective cross-pollination is the simultaneous opening of the flowers on both trees, known as bloom time overlap. Pollination groups classify varieties as early, mid, or late bloomers. A successful pollinator must be in the same group or an immediately adjacent group. If one tree finishes flowering before the other begins, the insect-mediated transfer of pollen cannot occur.
Proximity and Grafting
Pollen is primarily transferred by foraging insects, especially honeybees, which necessitates that the trees be planted within a reasonable distance of each other. While some sources suggest effective pollination can occur up to 500 feet, a more reliable distance for consistent fruit set is typically within 100 feet. Closer proximity ensures a higher concentration of pollen transfer, which is especially important during unfavorable weather when bees are less active.
For gardeners with limited space, a practical alternative to planting a second entire tree is to graft a branch from a compatible pollinator variety onto the existing plum tree. This method allows the single tree to produce two different types of blossoms, ensuring the necessary genetically distinct pollen is available directly within the canopy. This technique effectively solves the need for a separate pollinator tree.