Eight Reasons Your Lilac Bush Won't Bloom

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.

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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 6 hours of sunlight every day. If your lilac bush is not blooming, check to see if your site is too shady.

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 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.

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3. It's Over Fed

   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.

    
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4. It's In Shock

   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.

5. It's Dry

   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.

6. You're Improperly Pruning

   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.

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7. Your Soil is Imbalanced

   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.

8. 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. 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!