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Why Did My Lilac Stop Blooming?

Updated on January 18, 2017
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Caren White is a Master Gardener and instructor at Home Gardeners School. She has been a volunteer at Rutgers Gardens for over a decade.

Lilac | Source

You've had a lovely old lilac bush in your yard for years, but lately it seems to be blooming less or not at all. It looks healthy with no signs of disease or pests. So why won't it bloom? There are several reasons why lilacs stop blooming, most of them easily correctable.

Is it getting enough sun?

First, take a look at where the lilac is growing. Is it getting enough sun? Lilacs need full sun to bloom. Full sun is defined as at least 6 hours of direct sunlight each day. Are there surrounding trees that have grown and filled out over the years so that now they are shading your lilac? Large trees and large lilacs are not easily moved so in this case you might want to consider propagating your lilac and planting the resulting plants in a sunny location. Within 3 to 5 years, you will have lovely, blooming new lilacs.

Does the soil have too much nitrogen?

Next, you should check the soil surrounding it. It might have too much nitrogen, especially if your lilac is growing near your lawn. Lawn fertilizers contain a lot of nitrogen. Remember, nitrogen encourages the growth of foliage at the expense of flowers. A soil test can tell you if there is too much nitrogen. Call your local Extension office for a soil test kit and instructions on how to gather samples. If the test indicates too much nitrogen, an easy way to rebalance the nutrients in your soil is through the use of mulch. Wood chips or sawdust are excellent ways to soak up excess nitrogen from your soil.

Is it pruned correctly?

Pruning can be a reason why a lilac doesn't bloom if it is done incorrectly. Lilacs are shrubs. There are two types of shrubs, ones that bloom on "new wood" i.e. this year's growth and shrubs that bloom on "old wood" i.e. prior year's growth. Lilacs bloom on old wood. They should be pruned as soon as they stop blooming so that you don't cut off next year's buds. Removal of dead or diseased branches can be done any time.

Try the three year rejuvenation plan

Your lilac sits in full sun, has great soil and is never pruned in the spring or fall and it still won't bloom. Now what? A healthy lilac can live a long time. Eventually its branches become too old to bloom. It's time for a three year rejuvenation plan. Each year, for three years, remove 1/3 of the old stems. This encourages new growth which will produce blooms. At the end of the three years, you will have a healthy, new lilac bush that will produce loads of flowers for years to come.

© 2012 Caren White


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