Sometimes only part of the
bud is killed, and you still have a few flowers able to open on each
bud cluster. Warm weather in March had spring moving along a little
earlier than normal, until unusually cold weather in April damaged
all that tender growth. We have seen a lot of spring freeze injury
this year, and lilacs have been among the samples that have crossed
The location where your lilacs are planted could be another factor.
Lilacs need full sun to bloom well. Too much shade can reduce
flowering significantly, and deep shade will keep lilacs from
blooming at all. Eight to ten hours of sun daily is ideal; six
hours would suffice.
Well-drained soil is another consideration. Lilacs struggle along in
poorly drained soil, or die outright. They expend so much energy
trying to stay alive that they might not bloom in that situation.
When to Prune
Maintenance practices can also cause lilacs not to bloom well.
They "bloom on old wood," which means they form their flower buds
during the previous growing season. If you prune lilacs in the fall,
you remove those flower buds, and will not get to enjoy any of that
heavenly fragrance. Many spring-blooming plants bloom on old wood,
and all should be pruned when they finish blooming in the spring,
before they start to form next year's flower buds. You lilac is
young enough that you should not have to prune it much yet.
How you prune will also impact how well they bloom. Lilacs should be
pruned by removing the oldest, thickest stems at ground level. The
plant will respond by sending up a flush of growth from the roots.
Remove weak spindly shoots, and keep well-spaced, robust shoots.
This keeps the interior of the shrub open to better air circulation
and sun penetration, which makes for a healthier lilac. Lilacs do
not lend themselves to shearing the way you would maintain hedges of
privet or yew. Shearing removes the tip of each stem, which is where
you usually find flowers on lilacs. If your lilac was sheared at the
wrong time of year, you would have removed all of the flowers. If
you prune as described above, the flower buds on the remaining stems
would have been left to bloom for you.
Lilacs do not require a high
fertility level. If you fertilize a young plant heavily to encourage
it to grow faster, it may put on leafy vegetative growth at the
expense of flowers. Ornamental shrubs and trees generally do not
require the level of fertility that lawns, annuals, and some
vegetable and fruit crops require. You should always base their
fertilization on soil test results.
Soil test kits are available from your local Penn State Extension
office for a nominal fee. In Allegheny County, consumer soil test
kits cost $12 each, and come with detailed instructions for taking a
good soil sample and information to help you understand your soil
Customers ordering multiple kits at one time pay $9 each for any
additional kits. (You should take separate tests for lawns,
vegetable gardens, shrub borders, etc. since recommendations are
based on the crop you tell the soil lab you will be growing on the
site). Send a check made payable to Penn State Extension to Penn
State Extension, 400 North Lexington Street, Pittsburgh, PA 15208.
Write Attn. Soil Test Kit in the lower left corner of the envelope.
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