Plums, which belong to the Prunus genus of stone fruits, are a delicious addition to any home garden. Many gardeners are confused about the requirements for a plum tree to produce fruit. The presence of flowers does not guarantee a harvest, leading to the question of whether a second tree is required. The answer depends entirely on the specific type and variety of plum tree planted. This guide clarifies the different pollination needs and offers practical solutions for successful fruiting.
Plum Tree Pollination Requirements
Whether a second tree is necessary depends on the plum variety’s genetic makeup and fertility status. Plum trees are categorized as either self-pollinating (self-fertile) or cross-pollinating (self-unfruitful). A self-fertile plum can produce fruit when its own pollen fertilizes its flowers, allowing it to yield a crop as a solitary tree.
A cross-pollinating plum requires pollen from a different, compatible plum variety to set fruit. Without a partner, the tree will flower but fail to develop a harvest. Even self-fertile varieties often produce a heavier and more consistent crop when cross-pollinated by a partner tree.
A tree’s fertility is linked to its lineage, generally divided into European plums (Prunus domestica) and Japanese plums (Prunus salicina). These groups have distinct pollination habits. Knowing the cultivar chosen is the first step in ensuring fruit production, as a mismatch will result in no fruit.
Selecting Compatible Pollinator Varieties
Planting two different plum trees is insufficient; the selected partners must be compatible, and their bloom times must overlap. European plums (Prunus domestica), such as ‘Green Gage’ and ‘Stanley,’ are often self-fertile, but their yield improves with a compatible European pollinator. If cross-pollination is required, European plums must be paired with another variety within the Prunus domestica species, like a damson or a different European cultivar.
Japanese plums (Prunus salicina), including ‘Santa Rosa’ and ‘Shiro,’ are almost always self-unfruitful and require a different Japanese variety nearby. These trees rely heavily on cross-pollination for fruit set. The pollinator’s flowers must be open and releasing pollen simultaneously with the main tree’s flowers, which is why varieties are grouped by their general bloom period.
A common mistake is assuming that any two plum trees can pollinate each other, but European and Japanese plums generally do not successfully cross-pollinate due to genetic incompatibility. For instance, a European ‘Italian Prune’ cannot pollinate a Japanese ‘Methley,’ even if their bloom periods align. Pollen transfer is primarily facilitated by insects, especially honey bees, which must visit flowers on both trees within a short distance, ideally less than 100 feet.
Solutions for Single Tree Owners
For gardeners with limited space or those who have planted a self-unfruitful plum without a partner, several practical options exist beyond planting a second full-sized tree. One effective technique is grafting a compatible variety directly onto the existing tree. This process involves attaching a small branch, called a scion, from a compatible pollinator to a limb of the original tree.
Grafting creates a “cocktail tree” where a single plant produces two or more varieties, ensuring the necessary pollen is available on the tree. The most important step is aligning the cambium layers of the scion and the host branch so the tissues can fuse. This permanent, space-saving solution turns a non-fruiting tree into a productive unit.
A temporary but reliable solution is the “bouquet method,” useful while a new pollinator is growing or during low bee activity. This involves cutting branches of a compatible plum variety in full bloom and placing them in water near the non-fruiting tree. Bees will visit the cut flowers and carry the pollen to the main tree.
Another option for restricted spaces is growing a dwarf, compatible pollinator in a large container. The potted tree can be moved close to the main plum tree during the bloom period to ensure cross-pollination. These steps provide alternatives to help a solitary plum tree produce a good harvest, whether through permanent genetic modification or seasonal assistance.