A Blooming Success

Discover why your plants are not flowering.

"My lilacs didn't bloom this year. I pruned them, fertilized and did everything right. Can you help?"

This is just one of the many blooming mysteries I am asked to solve each year. Unfortunately, there is no single, easy solution. The cause for non-blooming plants can be anything from improper care and unsuitable growing conditions to the weather. So before you give up on your garden, let's unravel the mystery behind why some of our favorite plants fail to bloom. It might be an easier fix than you think.

Timing Is Everything

I'll start with lilacs (pictured at right), since they are one of the most common non-bloomers. Like forsythia, bridal wreath, spirea and other spring flowering shrubs, lilacs set their flower buds in late summer. So if you prune these plants after the buds are set-from summer through the next bloom time—it will eliminate the spring flowers. If you do need to prune, you should do so right after the plant has flowered.

If pruning is not the problem for your shrubs, then take a look at the winter weather conditions. Many plants like forsythia (below right) or oriental wisterias fail to bloom after a cold winter. While we can't control the weather, we can select plants with flower buds that are more likely to survive winter. There are many to choose from.

The University of Minnesota Landscape Arboretum has introduced many cold-hardy plants, including Meadowlark forsythia and Minnesota snowflake mockorange. If you live in Zones 4 to 5 and are looking for wisteria, try the Kentucky cultivar (Wisteria macrostachya). Unlike its oriental cousins, this wisteria has shorter, 12-inch blooms that appear with the leaves. It's not as impressive as a Japanese wisteria in bloom, but it's certainly better than no blooms at all.

Southern gardeners have the opposite problem with weather. Plants in warmer zones may not have blooms due to a lack of cold. Certain plants like lilacs and spring-flowering bulbs need a cold period to set flowers. If this affects you, look for varieties that set blooms in your region, or buy precooled bulbs and flowering plants suited to your mild climate.

Late-spring cold snaps can interfere with some flowering plants. Though they are cold hardy when dormant, the flower buds are subject to frost damage as the protective bud scales separate, exposing the tender petals. Some early-spring blossoms are damaged by the cold, while others never expand beyond the swollen bud stage.

Older and Wiser

Another reason a plant might lack blossoms is from a lack of maturity. Flowering is part of the reproductive process in plants, and they need to reach maturity to reproduce.

For annuals, this happens in the first year. For biennials and most perennials, flowers emerge in the second year. And for trees and shrubs, it could be years.

Most nut trees don't blossom and produce fruit until they are 15 years old or more. Standard apple trees are usually 6 or 7 years old before they begin to flower. Landscape plants like wisteria and trumpet vine may take as many as 7 years to reach a flowering stage. In these cases, all you can do is be patient.

Excess fertilization can also interfere with flowering. For example, trumpet vines love nitrogen and will steal it from any source their roots can reach. This overindulgence leads to large plants that are covered with leaves but lack blooms.

Avoid high-nitrogen fertilizer near these plants. And if that doesn't work, try giving your trumpet vine a little root pruning. Don't overdo it—that can cause your plant to die—but a little can help encourage flowering.

A lack of other nutrients, such as phosphorous, can also result in a lack of blooms. This nutrient encourages root growth, flowering and fruiting. But don't reach for the fertilizer until you get your soil tested. Many soils are already high in phosphorous, and adding more can be harmful to the plant and the environment as well.

Sunlight can also interfere with flowering, so make sure your plants have proper growing conditions. Check the label or ask your local Extension service to match the right plant to your growing conditions.

Next time you need to solve a blooming mystery, take a few clues from your growing environment and gardening practices. You might be surprised to find that the answer is likely within your reach!