It is usually quite difficult to determine why a shrub or tree fails to bloom. Most often the problem is the plant’s health, related to weather or environmental factors. Sometimes, the gardener has grown the plant poorly. Here are the seven leading causes:

1. High much nitrogen? The nitrogen to carbohydrate ratio (C:N) is a common fault. Too much nitrogen fertilizer encourages vegetative growth at the expense of flower production. Withholding nitrogen (particularly lawn fertilizer) application prior to bloom is the remedy. Root pruning around the shrub or tree’s drip line maybe another alternative.
2. Soil nutrition? A deficiency of phosphorus in the soil will inhibit blooming. To correct, dig a shallow trench around the plant. For each 3 feet of soil removed from the ditch, thoroughly mix a cupful of super-phosphate, or 2 cups of bonemeal, or a cupful of 0-20-20 into the dug soil and return to the soil.
3. Sun or shade? Shrubs and trees, which prefer a sunny location, fail to bloom in shade. Shade loving plants bloom more heavily in sunny locations, but plant health may decline afterward.
4. Plant spacing? Competition among nearby tree and shrub roots for moisture and nutrients may discourage blooming. Do not crowd plants.
5. Planting depth? If trees, shrubs or perennials are planted too deeply, the roots may lack water and oxygen.
6. Time of pruning? Pruning at the wrong time of the year may deter flower bud initiation or remove flower buds already formed. As a general rule, prune summer flowering trees and shrubs in late winter and spring bloomers within 4 weeks after petals fall.
7. Root sucker and shoot sprout removal? Vigorous root sucker and sprout growths around the plant base or densely thick on branches reduce flower bud initiation. Prune off sucker and sprout growths anytime that you see them.