Lilacs need sunlight to bloom properly

Posted6/10/2018 6:00 AM

Q. A relative gave me a small lilac bush several years ago. Although it has been growing nicely, it produces leaves and no flowers. Each year I am disappointed when there are no blooms to enjoy. What can I do?

A. After waiting all winter for the arrival of their beautiful scent and lovely color, it is always disappointing if blooms fail to appear. There are a number of reasons why this may occur.


Most commonly, excess shade is to blame as lilacs bloom best in full sun, and most varieties require at least a half day of sun to develop flowers. If your bushes are located where they are shaded all day, it is unlikely they will bloom. Maybe they were initially planted in an unsuitable location, or as is often the case in urban landscapes, once neighboring trees grew taller and fuller, they received less and less sun. Perhaps you have other shrubs nearby with heavy foliage. You may need to thin or trim them to make sure your lilacs are getting more sunlight. You may even need to move your bush to another location with less shade.

Your pruning practices also need to be considered. If you prune lilacs drastically, it may take three to four years before you see blooms again. If you have an overgrown bush and need to get it under control, cut out the oldest third of the shrub each year over a three-year period. This will help restore the bush to a manageable shape and stimulate blooms. On the other hand, if you prune lightly to shape the bush, but you wait until the middle of summer to take your trimmers out, you might not see flowers the next spring. This is because lilacs set their flower buds for the following year soon after the plant finishes blooming. It is best to prune immediately after the spring flowers fade.

If your bush hasn't bloomed, you may have provided it with extra fertilizer thinking you might get some action. Actually, lilacs don't need to be fertilized as they are not heavy feeders. When fertilizer nutrients are readily available, in particular nitrogen, the result is extra leafy, vegetative growth at the expense of bud development. Hold off on feeding your lilacs, and with time you should see blooms return.

Is your bush located where water doesn't readily drain away? This may have a negative impact on your plant. Lilacs like well-drained soils. Excess moisture in the form of poorly drained soil is associated with root rot and/or failure to thrive. You may need to move your bush to another site or plan to amend your current site with organic material, which will encourage drainage.

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-- Mary Moisand

• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines, and University of Illinois Extension, North Cook Branch Office, Arlington Heights. Call (847) 298-3502 on Wednesdays or email Visit

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