Gadenin日本語Get the appTwo different problems, depending on the type
A tree that flowers heavily and sets nothing is nearly always a sweet cherry standing alone. Sweet cherries carry a self-incompatibility system that rejects their own pollen, and it also rejects pollen from other trees that share the same incompatibility group. Planting two sweet cherries is not automatically enough: two trees from the same group are as sterile together as one tree by itself.
Sour or acid cherries, the cooking types, are self-fertile. One tree on its own sets a full crop, and it will also pollinate sweet cherries that flower at the same time. If you have room for a single tree and want fruit without arithmetic, that is the type to plant.
There is a middle category of self-fertile sweet cherries, bred specifically to sidestep the problem. They crop alone, though even these set more heavily with a second tree nearby. Whichever you have, the practical question is the same: is there compatible pollen open on the same days as your blossom?
| Type | Self-fertile? | Partner needed | Typical use |
|---|---|---|---|
| Sweet, standard | No | Yes, different group, same flowering time | Eating fresh |
| Sweet, self-fertile selections | Yes | No, but improves set | Eating fresh |
| Sour / acid | Yes | No | Cooking, preserving |
| Duke (sweet x sour) | Partly | Usually yes | Both |
Flowering times have to overlap
Compatibility is only half the requirement. The two trees must have open flowers at the same time, and cherry blossom lasts a short while: roughly 7 to 10 days per tree in mild weather, and as little as 4 days if it turns hot. Trees described as early and late flowering can miss each other entirely in a warm spring.
Watch your own trees rather than trusting a catalogue. Note the date the first flowers open and the date the last petals drop, for every cherry within about 100 feet (30 m), including neighbors' trees and wild cherries in a hedgerow. Two seasons of those notes tell you exactly which trees are actually available as partners, which no chart can.
If the overlap is marginal, a third tree flowering in the middle solves it more reliably than trying to shift bloom times. Ornamental flowering cherries are usually not useful here: many are sterile or triploid and produce no viable pollen.
Record first bloom, full bloom and petal fall each year for each tree. After three years you can predict overlap in advance and know whether a poor set was a pollination failure or a frost.
Get the insects working
Cherry pollen does not travel on wind in any useful quantity. It moves on bees, and cherry blossom opens early in the season when bee activity is unreliable. Cold, wind or rain across the flowering week will empty a tree of fruit even when both trees are perfectly compatible.
Bees fly properly above about 55F (13C) in calm conditions, and hardly at all below 50F (10C) or in steady rain. You cannot change the weather, but you can make the few flyable hours count: have something else in flower nearby so bees are already working the area, keep the tree out of wind, and avoid spraying anything at all while flowers are open.
- Plant early nectar close by Bulbs and early perennials flowering within 30 feet (10 m) of the tree bring bees into the area before the cherry opens. A tree that bees are already visiting sets better than one they have to discover during a four-day window.
- Never spray during bloom No insecticide, and no fungicide unless it is explicitly cleared for use at blossom, from first open flower to petal fall. Aphids can wait two weeks; the pollination window cannot.
- Hand pollinate if the weather closes in If it rains through the whole bloom, take a soft brush, collect pollen from the open flowers of the partner tree and dab it into the center of flowers on the other. Work in the middle of the day when the flowers are dry. Thirty flowers done properly is worth more than two hundred done fast.
- Use a cut branch as a mobile partner If your only compatible tree is out of reach, cut a flowering branch from it, stand it in a bucket of water under your tree, and top up the water daily. It will shed viable pollen for several days. This is the standard fix for a lone tree in a small garden.
Telling a pollination failure from a frost
Both leave you with no fruit, but the evidence differs and the fix is different. Open a failed flower and look at the base of the style. A frosted flower has a blackened center, visible within a day or two of the cold night, and the whole flower browns and hangs on limply. A flower that simply was not pollinated stays clean and pale inside, and drops cleanly a week or two after petal fall.
There is also a normal drop. A cherry sets far more flowers than it can carry and sheds a proportion of small green fruit a few weeks after bloom. Losing a third of the set at that stage is expected. Losing all of it, with clean abscission scars and no blackening, points at pollination.
If the diagnosis is pollination, the answer is another tree, and it is worth planting it immediately: a new tree needs three years before it contributes meaningful pollen. If the diagnosis is frost, the answer is site and protection: row cover thrown over a dwarf tree on a clear, still night at bloom is entirely practical, which is one more argument for keeping the tree small.