Why Plants Don't Bloom
Most gardeners spend hours pouring over gardening books and catalogs looking for the perfect blooming plants for their gardens. Once the selection has been carefully made, the gardener plants and tends to the new plant with anxious anticipation for the magnificent show of flowers the following year. And then... no blooms. Why would this happen? The following conditions may account for this gardening frustration.
Many woody plants go through a period of growth called the "juvenile stage" in which the plant does not flower. This stage occurs early in the life of a plant. It is sometimes characterized by a smaller or different leaf shape than is found on older plants of the same species. During this stage the plant produces an abundance of leaves and new growth, but does not flower. Flowering is prevented by a complicated chemical balance within the plant. This juvenile stage can last two to three years in shrubs and more than five years in trees. There is nothing a gardener can do to hasten this stage along. While patience may be difficult, remember that your plant is growing and producing more branches on which to produce flowers. So when your plant does begin to flower, it will do so more profusely than it would have in previous seasons.
Older plants, as they begin to decline will begin to produce fewer blooms. Some older plants will bloom magnificently before they die. It is nature's way of producing seeds for future generations of plants.
Temperature can play an important role in the flowering of many plants. When winter temperatures are extremely cold, flower buds may be killed; and therefore, the plant will produce fewer flowers. Usually you can see the brown and dead flower buds on the plant. The same situation can happen in the spring if there is a late freeze. Flower buds which have swollen and are ready to bloom may be killed if temperatures drop below freezing.
Some plants are subject to a phenomenon called "alternate flowering." This type of plant will frequently flower heavily in one year and then fail to flower for one or two additional years. This is a natural phenomenon and there is nothing a gardener can do to prevent the occurrence. Flowering dogwoods and crabapples are often subject to alternate flowering.
Sun loving flowering trees and shrubs require at least 6 hours of full sun to bloom profusely. If there is not enough sun, the plant may grow well, but will not flower as expected. Sometimes a plant which has flowered well for years begins to flower less profusely. This problem can often be traced to a change in the amount of available light. This may be caused by the growth of neighboring trees and shrubs which are now casting shade onto the plant.
Shade loving plants, such as azaleas, laurels, pieris and rhododendrons, still require a few hours of morning sun to bloom. Flowering trees and shrubs which are planted in very shady spots will produce few or no blossoms.
Many gardeners note that plants can be very vigorous growers and have a great deal of foliage and branching, yet fail to bloom. The vigorous growth is often caused by excessive fertilization, particularly with nitrogen, an element which promotes vegetative growth rather than flowering. To induce a plant under such conditions to bloom, decrease the rate of fertilization and water the plant thoroughly to wash the excessive fertilizer from the root area. It may require a year or two before the effect will be apparent on trees or shrubs.
Annuals and roses, on the other hand, are heavy feeders and require ample fertilizer to bloom profusely throughout the spring and summer.
Lack of flowering in plants can also be related to improper pruning. Prune spring flowering trees and shrubs immediately after they bloom. These plants produce the following year's flower buds in early summer. If a gardener prunes spring blooming plants during the summer, fall or winter, s/he will be removing the flower buds.
Summer blooming plants, such as crape myrtle, roses and butterfly bush bloom on new wood and should be pruned in late winter or very early spring.
These six conditions can explain the lack of flowering in most ornamental plants. It should be remembered, however, that a plant is a complex biological organism and that the flowering process is controlled by many factors in the environment, many of which are not fully understood.