Question: My ornamental apple tree didn’t bloom this spring. Why not?
Answer: There are a lot of reasons why a crabapple—or an apple tree, the two just being selections of the same species, Malus pumila—might not bloom. Here are some of the possibilities:
1. Your tree is too young. Like so many fruit trees, crabapples may take several years after planting before they start to flower. Usually 3 or 4, but up to 10 years when conditions aren’t ideal.
2. Your crabapple might be an alternate-year bloomer. It is quite normal for some cultivars to flower and fruit only once every two years. Or to bloom lightly one year and abundantly only the next. This kind of biennial flowering is called “alternate bearing” and it’s largely genetic, a holdover from wild apple trees, most of which bloom biennially. When buying a crabapple tree, try to look for an annual bloomer.
3. The tree is not getting enough sun. If the location has become too shady over the years, this can prevent flowering.
4. The apple tree is diseased. Apple trees suffering from various diseases (scab and fire blight are the worst) may see their flowering reduced or eliminated, especially when the disease goes untreated. It may be necessary to treat certain crabapples with fungicides in order to obtain good flowering.
5. The tree was over pruned or badly pruned. Usually, crabapples require little pruning, only enough to remove branches that are dead, damaged, diseased or rub together. Careful pruning, usually at the end of winter, has little to no impact on flowering, but severe pruning, such as cutting back most branches in an effort to rejuvenate an aging crabapple, often end up eliminating the buds that had overwintered on the tree. Very harsh pruning can also weaken the tree to the point it may take 2 or 3 years to recover and flower again.
6. A late spring frost killed the flower buds. This happens more often on other fruit trees (peaches, cherries, plums, etc.), as apple flower buds are quite cold resistant, but even so, it does happen. Depending on the stage of development of the buds when the frost hits, even a light frost of only 28 °F (-2 °C) can sometimes kill the buds, especially if it is prolonged.
7. The apple tree suffered drought the previous year. A dry summer can lead the tree to taking a year off blooming in order to recover from the trauma. If possible, always water your crabapple deeply during drought.
8. The growing conditions simply don’t suit it. Crabapples are actually quite adaptable, but won’t thrive in extremely acid or alkaline soil, where drainage is poor or in zones of constant dryness. To counteract poor soil, another possible problem, apply an all-purpose fertilizer in the spring.
9. The winter was too mild. This happens in areas with Mediterranean climates where crabapples are only very marginal garden choices anyway. Apple trees of all types need a long period of winter cold, often 1000 hours of temperatures below 45 °F (7 ° C), in order to prepare buds to bloom. If you live in such an area (USDA hardiness zones 8 or 9), look for varieties specifically adapted to mild climates that require less than 400 hours of cooling. Even then, if the winter was not cold at all, the tree won’t bloom.
10. The winter was too cold. At the opposite extreme, prolonged winter temperatures much below -40 °F (-40 °C) can kill flower buds and even leaf buds on some crabapples. Usually the tips of the branches are also killed. When this happens, the tree will leaf out late too, that season’s foliage coming from secondary buds buried under the bark … but there are no backup flower buds!
And there you go: just some of the many reasons why a crabapple tree doesn’t bloom.