Gardening Laidback Gardener Tip of the Day

Why Won’t My Plant Bloom?

20161110aWhen you buy a plant labeled with a beautiful picture of its flowers, you expect to see it bloom. But sometimes weeks pass, then months, then years and there are still no blooms. What went wrong?

There are several reasons why a plant doesn’t bloom. Here are 11 of them:

1. It’s the Wrong Season

Few plants bloom all year long. Most have a specific flowering season: that might be spring, summer, late summer, fall, etc. So if you plant a fall-blooming perennial or shrub in the spring, you can’t expect it to bloom any earlier. Before you give in to despair when a plant doesn’t flower within a few weeks of purchase, always check to see at what season you really should expect flowers.

2. It’s Too Young

Oaks may take 4 decades to reaching maturity and start to bloom.

We live in a world where you rarely ever have to wait for anything. You purchase something and in minutes it’s installed and ready to do whatever it is supposed to do.

Well, plants aren’t always like that. Sure, there are fast-growing plants such as annuals that should bloom pretty much from the time you buy them, but others take their sweet time. Many perennials won’t begin to bloom until their 2nd or 3rd year and a shrub can take longer: 4 or 5 years before flowering. Trees are usually very slow to bloom for the first time: 6 to 10 years is normal for a standard apple tree, for example, while you may need to wait 20 to 40 years for an oak to bloom.

Sometimes nurseries throw you by using special treatments to force a plant into bloom before its normal time. You see it blooming away in its pot, take it home, assuming it’s mature, and plant it… then have to wait 2, 3 or even 4 or 5 years before it really is mature enough to bloom regularly. Lilacs (Syringa spp.) certainly fall into the category of plants often sold in bloom, but which then can years to settle in and bloom in the garden.

3. The Growing Conditions are Inadequate

When the growing conditions plants receive don’t meet their needs, most simply won’t bloom… ever! More often than not, the location simply isn’t sunny enough for the species being grown. (Yes, there are plants that bloom in shady locations, but most really only flower in sun or partial shade). The location can also be too hot, too cold or too windy, and the soil may be too acidic, too alkaline, too dry, etc. The list of possibilities is very long. Check out what the plant is reputed to need and trying moving it to a spot where those needs can be met. Otherwise it simply won’t flower.

4. The Local Climate is Too Cold

Sometimes it’s not just the spot where you planted you’d need to change, you’d have to move to a warmer climate entirely! A climate that is too cold can kill the plant over the winter or at least set it back severely, but it is also very common for plant grown under colder conditions that Nature designed it to tolerate to look fine, but simply not bloom.

This forsythia only bloomed at the bottom, where it was covered by an insulating layer of snow. The flower buds on the upper part mostly froze over the winter. Photo: Cooperative Extension, University of Maine

This is especially true of spring-blooming trees and shrubs. You see, their flower buds are often less hardy than their leaf buds. When you plant them in a climate that is too cold, the plant may therefore survive and even appear to thrive, but it either never blooms or only does so after a particularly mild winter. Forsythias (Forsythia spp.), mock oranges (Philadelphus spp.) and rhododendrons and azaleas (Rhododendron spp.) are examples of plants that can produce perfectly healthy foliage year after year, yet have a hard time flowering when the local climate is too cold for their tastes. Unfortunately the hardiness zones indicated on plant labels often indicate the coldest zone in which you can expect it to survive, not the coldest zone in which it you can expect it to flower. If you suspect that a given plant might be of borderline flower bud hardiness, always check with a local expert for recommendations on varieties that will bloom in your climate.

5. The Local Climate is Too Hot

The opposite is also possible. Many plants native to cold climates, including apple trees (Malus spp.), lilacs (Syringa spp.) and most spring-flowering bulbs, to name just a few, absolutely depend a prolonged period of cold in order to bloom. In too mild a climate, they may put out foliage, but won’t bloom. That’s why you don’t find many apple tree orchards in southern Florida!

6. The Flower Buds were Killed by Frost

Frost at the wrong time can be deadly to nascent flower buds.

Another weather effect that may explain the lack of bloom is late frost, one that occurs after the plant, usually a tree or shrub, has started to awaken from its winter dormancy. The same flower buds that could take -5?F (-20?C) when the plant was deep in dormancy may now die at only 1 or 2 degrees below freezing once the plant’s growth is underway, causing the flowers to abort. Actively growing plant parts are rarely very frost resistant.

7. The Growing Season is Too Short

In northern regions, the cold nights of fall sometimes arrive too quickly for certain late-blooming plants. If so, they may produce flower buds, but they rarely succeed in opening. For example, perennial hibiscus (Hibiscus moscheutos) and several bugbanes (Actaea spp., formerly Cimicifuga spp.), though hardy enough to survive cold winters, rarely if ever bloom in my USDA zone 3/AgCan zone 4 climate. The season simply isn’t long enough.

8. The Plant Needs Short Days

Thanksgiving cactus need short days in order to bloom.

Some plants flower only under the influence of short days (less than 12 hours of sunlight per day). Outdoors that’s rarely a problem outside of Equatorial regions, as days naturally shorten in the fall, encouraging such plants to bloom. But the situation is different in our homes, which we tend to keep well lit in the evening, extending the day length. To bloom plants like poinsettias (Euphorbia pulcherrima), Christmas or Thanksgiving cacti (Schlumbergera spp.), kalanchoes (Kalanchoe spp.) and certain begonias (Begonia spp.), you need a spot where they won’t receive artificial lighting in the evening from the end of September on. You’ll find more information on that subject here.

9. Too Much Fertilizer

Too much fertilizer, especially a nitrogen-rich fertilizer (the first number of the 3 written in large letters on the label) can prevent plants from blooming. Nitrogen tends to stimulate excessive growth of green plant parts (stems and leaves) at the expense of flowers. Some plants, including nasturtium (Tropaeolum majus), are particularly affected by the overuse of nitrogen fertilizers.

Oddly enough, insufficient fertilizer is rarely a problem when it comes to stimulating bloom. Most soils that are rich enough in minerals to allow plants to survive are also rich enough to allow them to bloom. In these cases, applying more fertilizer is more of a way of increasing bloom than actually stimulating it. The idea, highly promoted by the fertilizer industry, that fertilizer stimulates bloom is simply a sales gimmick. So don’t run out and buy fertilizer if your plant doesn’t bloom: that won’t be the real problem. Find the real cause first.

10. Pest Damage

Scale insects can sap a plant’s energy and prevent it from blooming.

The presence of borers, scale insects, mealybugs, mites, aphids, etc. on a plant can weaken it and prevent flowering. An appropriate treatment may be necessary to regain control. Nibbling pests, like deer, marmots or rabbits, can certainly keep a plant from blooming as well. In some cases, a repellent may help. In others, nothing less than good fencing will stop them.

11. Pruning at the Wrong Season

Pruning at the wrong time of year can certainly prevent plants from blooming. You can’t simply cut most plants back at just any time of year, especially just before they are due to bloom, and still expect them to flower, because your pruning efforts would well be suppressing the flowers to come.

But you sometimes have to think much farther ahead than just a few weeks before you prune. Many trees and shrubs, especially those that bloom in the spring, flower on old wood that is, they begin producing their flowers buds the previous season. For example, the ever popular lilac (Syringa spp.) begins getting ready for its next blooming within 3 to 4 weeks of the previous year’s flowers fading. The usual rule of thumb for spring-flowering shrubs is to prune them “within two weeks of their previous blooming”, otherwise you may inadvertently cut off the flower bulbs for the upcoming year.

There you go: 11 reasons that can explain why a plant doesn’t bloom. It’s now up to you now to determine what might be keeping your plants from blooming under your conditions!20161110a

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

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