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Monday, May 16, 2011

Why Lilacs Don't Bloom

Courtesy of Rob's Plants
Around there, the Lilacs (Syringa vulgaris) are in full bloom. Just a short walk outside and their perfumed scent hits you before your eyes can even find them. But what does it mean if the shrub doesn't bloom? I was asked this question last weekend by a friend. Last year she pruned it serverely after it flowered, with the hopes of rejuvenating it so it would be overflowing with blooms the following spring. However, this year, not one bloom appeared.

There are a few reasons I can think of as to why a Lilac shrub wouldn''t bloom:

1. Pruning
New flower buds are formed soon after the current year's blooms die back. To ensure abundant flowering the next year, spent blossoms should be cut off and the flowering stem should be pruned back to a set of leaves. Waiting too late to prune will remove the new buds that have formed for the following year.

2. Immaturity
Most varieties of Lilacs need three to four years to grow and develop before they produce their first blooms.

3. Soil pH
Lilacs prefer sweet soils (slightly acid to alkaline) with a pH between 6.0 and 7.0. If the soil is too acidic (aka "sour"), it should be amended with lime to help sweeten it a bit.
Never assume your pH - have it tested by your local garden center or Cooperative Extension Service before trying to alter it.

4. Fertilizer
In general, Lilacs don't need much fertilizer, but if you feel it is needed, Cornell University recommends a 5-10-10 (5% Nitrogen, 10% Phosphorus, 10% Potassium). Using the wrong type of fertilizer can be a problem. Fertilizers with higher Phosphorus will encourage flowering on plants and vegetables. Fertilizers with higher Nitrogen will help produce green leaves, but will hinder blooming. Apply fertilizer to the planting area in the spring, as new growth is beginning.

5. Sunlight
Lilacs need full sun. If the shrub is in partial sun or shade, it will not bloom well.

6. Water
Lilacs need do not like wet feet, so be sure they are not over-watered. They do best in soil that is well drained.

7. Transplant shock
If the plant was moved since the last blooming period, it may take a year for it to recover and be happy.

Did you know?
The story of Lilac, according to Greek mythology, begins with a beautiful nymph named Syringa (Lilac's botanical name). Captivated by her beauty, Pan, the god of the forests and fields, chased Syringa through the forest. Frightened by Pan's affections, Syringa escaped him by turning herself into an aromatic bush - the flower we now refer to as lilac!

5 comments:

  1. The obvious reason for lack of bloom is lack of winter chill. An unseasonably warm winter may discourage bloom. That's why lilacs do not bloom in the south. Lilacs were my father's favorite flower and we had huge lilac bushes in north Georiga. They are iffy bloom in the Atlanta area and do not thrive near the Florida line where I garden now.

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  2. Very true Nell Jean! Here on Long Island, however, we had quite a cold, snowy winter so that wouldn't have been the case with my friend's shrub. But interesting to hear how they can grow in northern parts of GA - I didn't know that!

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  3. Lilac blossoms form on 'Old' wood. If your friend pruned the bush back hard then most of its energy in putting out new green growth. Lilacs flower best and more prolifically if they are never pruned but if you do have to prune them hard, don't expect blossoms for up to five years!

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  4. HI Tanya - That could very well be the reason it's not blooming now. Thanks for your post!

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  5. Such wonderful tips Kate. There is nothing that smells so wonderful in the spring around here as the lilacs.

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