Why isn’t my lilac blooming?

By Melanie Mathieson, The Gardening Guru

Why isn’t my lilac blooming?
This question is one of the most common queries to garden advice columnists, including myself.
Here are some reasons as to why your lilac may not be blooming—and remedies. Follow this sound advice and you should see a change in the status of blooms on your lilac in the next few growing seasons.
Remember, patience is a virtue that often has to be practised in the gardening world.
•Reason #1: It’s not getting enough sun
The fact that lilacs prefer being located on a site with full sun is an understatement. To thrive and flower, lilacs need a minimum of six hours of sunlight every day.
If your lilac bush is not blooming, check to see if your site is too shady.
If is it a smaller shrub, you may be able to relocate it to a sunnier spot (just be careful that you dig it up using a generous distance away from the tender young roots).
Reason #2: It’s too young
A lilac will not bloom before its time, and most varieties of lilacs won’t bloom until they reach at least three-six years of age.
Years one-three are spent growing and developing both the root system and the upper foliage. This is necessary for the shrub to provide itself with the ability to obtain water and nutrients, as well as complete the photosynthesis process, in order to produce enough energy in the future to also produce flowers.
Only when the lilac is good and ready will it produce its first blooms.
When they finally do bloom, the first few years can be less than spectacular. Don’t worry, be patient. It’s worth the wait.
Hint: Most lilacs purchased in containers have passed their first birthday and started to develop a good root system. They generally will flower sooner than bare-root shrubs.
Reason #3: It’s over-fed
As mentioned in previous columns, fertilizing needs great care and precision.
The primary nutrients in fertilizers are nitrogen, phosphorus, and potassium (on the fertilizer package, they are listed in this order, N-P-K).
Nitrogen promotes growth above ground while phosphorus promotes growth below the ground (roots) and also is most responsible for flowering. Potassium helps with overall growth.
Using a fertilizer high in nitrogen will encourage your lilacs to produce an abundance of green leaves while, at the same time, prevent it from flowering.
Fertilizing lilacs is not mandatory and if your soil is nutrient-rich, your lilacs won’t need feeding more than once per year in the early spring (if at all).
When you fertilize, use one with twice the ratio of phosphorus to nitrogen in order to promote flowering. Bone meal is great fertilizer for lilacs.
Remember, grass craves nitrogen so if you’re fertilizing your lawn, your lilacs may be getting over fed. Make sure when fertilizing your lawn that you make a wide berth around the lilacs.
Reason #4: It’s in shock
If you’ve recently purchased a lilac for transplanting, it still may be adjusting to its new environment. Even if it was blooming when you bought it, you shouldn’t expect it to bloom for the next year or two following transplanting.
Lilacs need a fairly long period to settle in. Be patient—you may need to wait as much as three years before it fully recovers.
Reason #5: It’s dry
Lilacs don’t like their feet constantly wet, but summer droughts also can take a toll on the next year’s flower buds.
Keep your lilac on a regular watering schedule and adjust it for heavy rain or extended periods of drought (just be sure not to over-water).
Reason #6: Improper pruning
If you wait too long to prune (after mid-summer), you’re going to be cutting off next year’s flower buds. Pruning should be done immediately after flowers die off because next year’s buds form shortly thereafter.
If your lilac bush has become overgrown, cut back only the oldest one-third of the shrub each year over a period of three years.
Reason #7: Soil imbalance
Lilacs prefer a soil pH from 6-7 (a little on the alkaline/basic side). If your soil is too acidic or missing certain nutrients, your lilacs won’t bloom.
Testing your soil is the only way to know. Inexpensive pH test kits are available at garden supply stores.
If the results indicate your soil is too acidic, spread wood ash or lime around the drip line of the bush for bigger and better blooms.
Reason #8: You’re growing the wrong variety
If you’ve purchased you lilacs from a reputable local nursery, this probably isn’t your problem, but as I mentioned in other columns, large box store garden centres sometimes stock zone inappropriate plants and shrubs.
Most common lilacs (Syringa vulgaris) need a cold winter to allow it to set buds and do fine in our area, but sometimes a new special variety may show up in the bulk stock (check the hangtag to make sure it is appropriate for a Canadian Zone 4 or less).
Reason #9: You’re not pruning away the root suckers
Always prune away the small shoots that come up through the soil in close proximity to the trunk. These root suckers are taking energy away from the main part of the tree, which is needed to produce flowers.
Good grooming and mulching also is important. As well, make sure there are no weeds close to the trunk competing for the nutrients.
Good luck—maybe next year will be the year!

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