Archive for Sunday, April 8, 2012

Garden Calendar: New life for lilacs that have lost vigor

April 8, 2012

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The common lilac, Syringa vulgaris, may be one of the most recognizable harbingers of spring in northeast Kansas. The shrub’s soft purple panicles emit a fragrance often emulated but rarely equaled, and they are often planted solely for the enjoyment of their spring blossoms.

Despite being long-lived, lilacs can lose vigor over time and will eventually produce fewer blooms or stop blooming altogether. There are two possible solutions to get blooms again in the years ahead: revive the shrub with a little tender loving care or consider planting other species of lilacs.

To rejuvenate, lilacs need a little pruning. The best time to perform the pruning is just after the blooms fade. (Lilacs can be pruned every year to encourage new, healthy growth.)

Begin by removing the largest stems at ground level. While this may seem counterintuitive, stems lose vigor over time. They are also likely infested with ash/lilac borer, an insect pest that typically does not kill the shrub but may cause wilting or kill individual stems. Also remove any dead stems or branches or stems that appear to be unhealthy.

If the lilac is a different color than the traditional light purple, or you know it is a newer variety, it may be grafted. If so, you will want to make the previously advised cuts above the graft union. Cutting below the graft union may trigger shoots to sprout from the rootstock. Shoots from the rootstock will likely produce less-desirable flowers than the grafted top of the plant.

You could also wait until this winter and prune the entire plant to near ground level, but you will lose blooms for a few years during the plants’ recovery.

After thinning the largest stems, work to remove the spent flower blossoms from the plant if it had any. Lilacs can handle severe pruning, so this is the time to reduce the height or size of the shrub if necessary. Leave at least a little foliage on each stem so the plant can continue to photosynthesize.

This is a good time to also note that if you are reducing the plant’s size because it is too large for the space in which it is planted, it might be time to move or replace it. You could prune it down every year, but why make the effort when there are smaller plants available?

Make cuts next to a bud or another branch, and preferably at a 45-degree angle in the same direction as the bud or branch to which you are cutting.

Shade could also be the culprit for a poorly-blooming lilac. If this is the case in your yard, cut the shrub back and move it to a place where it receives six to eight hours of direct sunlight per day.

If you want to replace your nostalgic lilac for one of its cousins, there are many to choose from. These can also be additions to the landscape rather than replacements.

Lilac options

Cultivars of Syringa vulgaris are common lilacs that have been selected and reproduced because of their unique flower color and/or size. More than 400 selections are available in a range of shades of pink and purple and white. Look for resistance to powdery mildew and purchase while in bloom so you know what you are getting for flower color and scent.

Meyer lilac, Syringa meyeri, is most typically available as a cultivated variety named “Palibin.” The species is similar in size to common lilac while “Palibin” grows to only 4 to 5 feet tall. Meyer lilacs bloom are resistant to powdery mildew and are considered the easiest lilac to grow, but they are less fragrant the common lilac.

Miss Kim Manchurian lilac, Syringa patula “Miss Kim,” is one of my favorites because it blooms a little later than common lilacs and has a distinct blue tint to its blossoms. Miss Kim lilacs are typically listed as reaching 3 feet tall by 3 feet wide, but I have seen a few reach 5 feet or more in good growing conditions.

Syringa reticulata — Japanese tree lilac — is another lilac cousin growing in popularity. This is a tree form as the name implies and some common cultivars are “Ivory Silk” and “Chantilly Lace.” They reach 20 to 25 feet tall and bloom in early to mid-June. The fragrance of this plant is much different from that of the common lilac and people typically either love or hate it.

Littleleaf, Pekin, Cutleaf, and Persian lilacs are also suitable species for our region.

—­ Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. Contact her or an Extension Master Gardener with your gardening questions at 843-7058.

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