Many home gardeners desire a bounty of fresh, homegrown cherries. Confusion often centers on the necessary conditions for a cherry tree to produce fruit. Unlike many fruit trees that bear a crop on their own, most cherry varieties require a specific biological partnership to transition from flower to fruit. Understanding pollination requirements is the most important factor determining whether a single tree will yield a harvest or remain ornamental.
The Core Distinction: Sweet vs. Sour Cherries
The most significant factor determining a tree’s pollination needs is the cherry type chosen. Cherries are broadly divided into two categories: sweet cherries (Prunus avium) and sour, or tart, cherries (Prunus cerasus). This distinction fundamentally changes whether a second tree is required.
Sour cherries, such as Montmorency or North Star, are generally self-fertile. This means a single tree can pollinate its own flowers and produce a full crop. The fruit is typically reserved for cooking or baking due to its higher acidity, as it is less often eaten fresh. Although one sour cherry tree is sufficient, planting a second, distinct variety nearby can sometimes result in a heavier fruit set.
Sweet cherries, including varieties like Bing, Rainier, and Lambert, typically require a partner tree. Most sweet cherry varieties are self-unfruitful (self-incompatible), meaning the tree cannot successfully fertilize its own flowers using its own pollen. This mechanism prevents inbreeding and requires pollen from a compatible cherry tree for fruit production.
Understanding Self-Fertility and Cross-Pollination
The necessity of a second tree for sweet cherries stems from a complex genetic system called self-incompatibility, controlled by specific S-alleles. If a pollen grain shares an S-allele with the receiving flower’s pistil, the flower rejects the pollen, preventing fertilization. Therefore, planting two trees of the same variety, such as two Bing trees, will not result in fruit production because the pollen is incompatible.
To ensure cross-pollination, growers of self-unfruitful varieties must plant a second variety with a different set of S-alleles. Modern breeding, however, has produced exceptions among sweet cherries. Varieties like ‘Stella,’ ‘Lapins,’ ‘Black Gold,’ and ‘Sweetheart’ are self-fertile, possessing a genetic mutation that allows them to fertilize their own flowers. These are excellent choices for gardeners with limited space for only one tree.
Self-fertile varieties can also serve as universal pollen donors for many older, self-incompatible sweet cherry varieties, provided their bloom times align. The presence of bees and other insects is necessary, as they are the primary agents for transferring pollen between flowers. Wind pollination is significantly less effective for cherry trees compared to insect activity.
Selecting the Right Pollinizer Partner
When a sweet cherry variety is self-incompatible, selecting the correct pollinizer partner requires both genetic compatibility and synchronized bloom time. The partner tree must be a different cultivar belonging to a distinct pollination group; for instance, a Bing cherry cannot be pollinated by a Royal Ann because they share the same incompatibility group (S-alleles). The trees must also have blossoms open simultaneously for successful pollen transfer, meaning a tree that blooms early will not pollinate a tree that blooms late. Compatibility charts often categorize trees into bloom groups (e.g., A, B, C) to simplify pairing.
The physical proximity of the two trees is also a practical factor, as pollinating insects, primarily honeybees, must easily travel between the blossoms. Closer planting, ideally within 50 feet, ensures the highest likelihood of successful cross-pollination, though 100 feet is often cited as a maximum. Planting a self-fertile variety like ‘Stella’ or ‘Black Gold’ simplifies selection, as they are compatible with most self-unfruitful varieties and are reliable pollen sources.