As far as a shrubs go, lilacs are a dream come true for the gardener. Once established, these landscaping beauties will throw out heavenly-scented, long-lasting blooms for years and years-and all with very little care and maintenance on our part. Why is it then, after weeks and weeks of anticipation and doing everything right, your lilacs always fail to bloom? Here are the eight most common reasons.
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 6 hours of sunlight every day. If your lilac bush is not blooming, check to see if your site is too shady.
A lilac will not bloom before its time, and most varieties of lilacs won't bloom until they reach at least 3 to 6 years of age. Years 1-3 are spent growing and developing. Only then, and only when they are good and ready, will they produce their 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 will generally flower sooner than bare-root shrubs.
Imagine stuffing yourself full of food and then trying to perform something that requires you to expend lots of energy (think Thanksgiving). This is how it is for lilacs getting too much nitrogen.
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. Phosphorus promotes growth below the ground (roots) and 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 a fertilizer with twice the ratio of phosphorus to nitrogen in order to promote flowering. Remember, grass craves nitrogen, so if you're fertilizing your lawn your lilacs may be getting over fed.
If you've recently purchased a lilac for transplanting, it may still 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. You may need to wait as much as 3 years before it fully recovers.
Lilacs don't like their feet constantly wet, but summer droughts 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.
If you wait too long to prune (after midsummer) 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 1/3 of the shrub each year over a period of 3 years.
Lilacs prefer a soil pH from 6 to 7 (a little on the alkaline side). If your soil is too acidic, or missing certain nutrients, your lilacs won't bloom. And testing your soil is the only way to know. Inexpensive test kits are available at more garden centers, or for the most accurate test, contact your county extension agency for labs in your area. If the results indicate your soil is too acidic, the International Lilac Society suggests spreading fireplace ash around the drip line of the bush for bigger and better blooms.
If you've purchased you lilacs from a reputable local nursery, this probably isn't your problem. Still, large discount garden centers sometimes stock zone inappropriate plants and shrubs. Most common lilacs (Syringa vulgaris) need a cold winter to allow it to set buds. If you live in an area of mild winters, a Meyer lilac (Syringa meyeri) may be a better choice for your garden.
If none of these reasons can be applied to your situation, consider giving your bush a light root pruning in early summer. Jam a sharp spade into the ground on two sides of the plant about 12 inches out from the trunk. And maybe next year will be the year!
About The Author: Ellen Brown is our Green Living and Gardening Expert. Ellen Brown is an environmental writer and photographer and the owner of Sustainable Media, an environmental media company that specializes in helping businesses and organizations promote eco-friendly products and services.
I have found lilacs tolerate slightly acidic and slightly alkaline soils quite well. And they do well on clay soils, which will tend to be alkaline. And while I agree with most of the statements made by the author, the best flowering lilacs I have observed are beside old, abandoned farm houses, where the shrubby tree is never pruned, or fertilized - just left alone.
re: " reason #7 - "Lilacs prefer a soil pH from 6 to 7 (a little on the alkaline side)." "
Um, sorry but if they prefer "a little on the alkaline side", that'd be 7 to 7.5, 6 to 7 is "slightly acid". So which is it?
7 is neutral on the pH scale, anything above that (7.1 to 14) is alkaline and anything below that (0 to 6.9) is acid.
I was wondering the same thing myself, knowing the ph scale quite well, that doesn't make a lick of sense to me.
I think what the author meant by "a little on the alkyline side" was "on the less acidic side." Most plants prefer acidic soil to alkyline, but on the pH scale of what most plants prefer, lilacs prefer "more neutral/alkyline" and less acidic soil.
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