The common lilac (Syringa vulgaris) is, surprisingly, a member of the olive family, and like the olive, has a long life. More than likely, it'll outlast the homes it surrounds as well as the people in them. Growing lilacs in climates warmer than USDA hardiness zone 9 poses problems for these cold-climate beauties that bloom in April and May. Their fragrance is distinctive, and in order for them to flower, protect them from a late frost by covering the buds in late winter. However, lilacs are one of the most hardy plants around and survive most swings in temperature.
If you are growing your lilac in a container, do not bring it indoors during the winter. They need the cold to set the buds for flowering.
Caring for Lilac Plants in Winter
A jar with lilacs overflowing and draping down to the kitchen table brings childhood memories into sharp focus. Add to that the unmistakable fragrance the bundle brings with it, and you're transported to a time long ago. Such is the pleasure of lilacs that bloom in the spring, even after a hard winter.
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Lilac hedges in winter need little attention. Preventing them from dehydration is your main concern. Dry winds and frozen ground contribute to the lilac becoming dehydrated. Water the plant well before the winter cold freezes the ground. When winter days bring a bit of sunshine, take the opportunity to give your lilacs a drink of water around their root area.
Another winterizing trick is to spread mulch around the base of the bush. During the winter when temperatures are extreme, roots "heave" and can penetrate the surface of the soil. The mulch keeps the roots warm.
Pruning Lilac Bushes
Good pruning practices for your lilac bushes and hedges is akin to good grooming. While the bush rewards you with beautiful scents and colors in the spring, you must care for it after the blooming period. The better you prune, the more likely it will survive a cold winter.
Start pruning your lilac bush when it's older than two years and after the spring blooming season. Cut dead flowers, damaged stems and thin out the suckers by at least 1/3. Late season pruning may put developing buds at risk. The Boomerang Purple lilac (Syringa 'Penda') blooms twice annually, and pruning after the first set of blossoms dies off encourages more growth and flowering in its second seasonal life.
As lilacs only flower at the tips of their branches, good pruning spreads the joy throughout the width and length of the bush, adding interest to the plant and encouraging new growth.
Lilac Plants in Winter
As the fall unfolds, the lilac bushes and hedges start preparing for winter. As a deciduous plant, the lilac loses its leaves, and the ground will be full of lilac debris. This shedding of leaves continues into the winter until the bush is bare. This is a good time to examine the lilac bush or hedge to determine any negative growth patterns to be addressed in the spring. Be careful not to prune at this stage, as budding has begun.
If the temperatures drop below -40 degrees Fahrenheit (Ouch!) wrap the bushes in burlap to protect them. Do the same when icy winds are projected. Keep the plantings away from buildings and be sure they get at least six hours of sunlight each day throughout the spring-summer-fall season. And just as extreme cold affects lilacs, so does high humidity.