While both cherry and apple trees belong to the larger Rosaceae family, the answer to whether one can pollinate the other is a simple and definitive no. Successful cross-pollination requires a degree of genetic compatibility that does not exist between these two distinct types of fruit trees.
Understanding Species Incompatibility
The fundamental barrier preventing an apple tree from pollinating a cherry tree, or vice versa, is genetic incompatibility at the genus level. Apple trees belong to the genus Malus, while cherry trees are classified under the genus Prunus, which also includes plums and apricots. This separation indicates a significant evolutionary distance, preventing the successful fusion of their reproductive cells.
When pollen lands on the receptive female part of a flower (the stigma), it must germinate and grow a pollen tube down the style to reach the ovule for fertilization. In cases of incompatibility, the female tissue chemically recognizes the foreign pollen as unsuitable. The pollen tube growth is either completely arrested or is too slow to reach the ovule before the flower withers.
The genetic information carried by the apple pollen simply does not contain the correct chemical signals to be accepted by the cherry flower’s reproductive system. This biological roadblock cannot be overcome by planting the trees close together or by having overlapping bloom times. For successful fruit set, the pollinator must be a compatible variety from the same or a very closely related species.
Specific Pollination Requirements for Apple Trees
Most apple varieties are self-incompatible, meaning they require a different, genetically distinct apple variety to act as a pollen donor. This donor variety must bloom at the same time as the primary apple tree to ensure the transfer of viable pollen by insects, primarily bees. Planting two trees of the same variety will not result in cross-pollination because their genetic makeup is identical.
The most effective pollen donors are diploid varieties, which have two sets of chromosomes and produce fertile pollen. Triploid varieties, such as ‘Jonagold’ or ‘Gravenstein,’ have three sets of chromosomes and produce sterile pollen, meaning they can be pollinated but cannot pollinate other trees. Growers often use flowering crabapples, which are also in the Malus genus, as effective pollinators due to their abundant and long-lasting bloom period.
For optimum fruit set, the pollen must be highly effective, not just compatible. Even among compatible apple varieties, the source of the pollen can affect the rate of pollen tube growth and the final fruit set. For instance, ‘Golden Delicious’ pollen may lead to a higher fruit set on certain varieties compared to some crabapple pollen sources.
Specific Pollination Requirements for Cherry Trees
Cherry trees, particularly sweet cherries, have a complex and specific pollination system governed by genes called S-alleles, which determine compatibility. Most sweet cherry varieties are self-incompatible and require a partner tree that possesses a different pair of S-alleles. If two varieties share even one S-allele, they will be partially incompatible, and if they share both, they are completely cross-incompatible.
Sweet cherry varieties are organized into incompatibility groups based on their S-alleles, and a successful pollinator must belong to a different group. For example, two varieties in Group I cannot pollinate each other, but either can pollinate a variety in Group II, provided their bloom times align. To simplify this process, many growers choose self-fertile sweet cherry varieties, such as ‘Stella’ or ‘Lapins,’ which possess a unique S-allele that overrides the incompatibility mechanism.
Sour cherries, unlike most sweet cherries, are generally self-fertile, meaning a single tree can produce fruit without a pollination partner. Even these self-fertile varieties may produce a heavier crop when cross-pollinated. The distinction between sweet and sour cherry pollination needs is a consideration for growers.