When Flowering Plants Don't Flower
by Don Janssen, Extension Educator
Spring-flowering shrubs like these Nanking Cherries can be
pruned immediately after flowering. Do not prune in fall or
winter or you will lose your beautiful blooms next spring
When gardeners plant flowering bulbs, vines, shrubs or trees, chances are that it's the flowers they're eager toss. When the plants don't perform, the obvious question is "Why?" Sometimes the answer is obvious.
With woody ornamentals, failure to flower is often simply a matter of age. These plants go through a juvenile growth period, when they produce shoots and foliage but don't flower. The length of the juvenile period can be a year or two or a dozen years or more, depending on the species and the cultivar. When the plants mature, they begin to produce flowers.
Many plants will respond to abundant fertilizer with abundant leafy growth at the expense of flower formation. This is most often seen in tomatoes, though it can occur in landscape ornamentals also.
A poorly selected planting site or improper planting can also interfere with flowering. Planting peony crowns or iris rhizomes too deep, for instance, will prevent flowering. Sun-loving plants planted in a shady spot may survive but produce only a few blossoms or none at all. Spring-flowering bulbs planted in poorly drained soil or too near a heated basement, where heat from the structure warms the soil and interferes with the bulbs' necessary cold treatment, will rot or simply fail to flower.
Plants that are only marginally hardy in our area may fail to flower most years. Many dogwood cultivars, for example, are spectacular farther south, but in Nebraska, their flower buds usually get frost nipped. Plants that are hardy may have flowers that are not - strawberries, for instance, and peaches. Even forsythia, that old standby, may lose its flower buds in an especially cold winter. Sometimes the buds above the level of a winter's insulating snow layer will be killed, while the ones below it will open as usual.
Forsythia and other spring-flowering shrubs set flower buds in the fall on one-year-old wood, so pruning them in the fall or during the winter removes the buds and so prevents flowering. Browsing deer and rabbits feeding on twigs in winter can have the same effect. No buds, no flowers.
The time to prune these plants is immediately after flowering, before they have a chance to produce the buds that will open into next spring's floral display.
It may take a little detective work to pinpoint the cause, but why a plant fails to flower usually isn't a major mystery. It usually has something to do with the plant's age, the planting site, nutrition or pruning, either by the gardener or Mother Nature and her helpers. It's unusual to have to look much further.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office