- Lack of sunlight - insufficient light reduces flower bud development
- Fertility - too much nitrogen fed to plants can over-stimulate vegetative growth, either delaying or preventing flower bud development
- Winter injury or chilling tender flower buds in one or more spring frost
- Pruning at the wrong time of year, essentially removing all flowering wood
- Alternative (biennial) flowering when a plant bears too much fruit and will not initiate new flower bud for the next year
All these factors are inter-related. While bad pruning practices may reduce flower bud numbers, good timely pruning practices increase blooming. Usually, an unpruned tree or shrub does not bloom heavily. A shrub or tree with an open branch canopy in full sun will flower reliably every year.
Prune spring flowering shrubs and trees immediately after flowering. These plants set flower buds on woody growth produced in the summer. Summer-flowering plants set their flower buds on spring wood in the same year when they bloom. They can be pruned in late summer or wait until late winter and early spring.