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Tales from a Plant Addict

Fun (& a few serious) facts, tips and tricks for every gardener, new and old.


One sure sign to me that Spring has taken hold and there's no turning back is lilacs beginning to bloom. Though lilacs are a very common sight around the U.S., they are native to Europe and Asia. There are about twenty different species of lilac, or Syringa, plus many different hybrids of these species. They are closely related to another common landscape shrub, Ligustrum, the privet.

Lilacs are considered to be deciduous shrubs or even small trees. Their size ranges from about six feet to over 30 feet tall. It is possible for the stems of lilac to be over twelve inches in diameter.

Most lilacs flower once a year in the spring. Flowers are produced in large clusters called panicles at the end of branches on old wood. Each individual flower is tube shaped, up to about a half an inch in diameter, and an inch long, though smaller flowers may be present.

The most common color of lilac flowers is pale purple—this is where we get the color name 'lilac'. There are cultivars available with white or pink flowers, or even purple edged with white. Victor Lemoine, a French plant breeder is credited with developing double-flowered cultivars which are commonly called French lilacs.

Growing lilacs is best done in a sunny site that has well-drained, slightly alkaline soil. The good news is alkaline soil is pretty easy to come by in central Illinois, since many soils are high in clay, which is alkaline. The bad news is that soils high in clay usually retain too much water and result in poor drainage of a given area. Hopefully you can strike a happy medium in your landscape with some careful amending and attention to site selection.

Everyone wants to know how to make their lilac bush produce more flowers. They are an extremely hardy shrub, often living for decades. Some have reportedly lived for centuries! This time of year I know we will get a few calls from people who have had a lilac in their yard "forever" but it doesn't flower anymore. And they want to know why.

There are a couple of possibilities. Lilacs flower on old wood. This means that they form next year's flower buds on this year's growth. If you decide to prune your lilacs, it needs to be done right after they flower. If you wait until later in the summer or fall, you risk pruning next year's flowers off!

After lilacs flower, they will produce seed pods if the flowers are not pruned off. Producing seed pods takes a lot of energy from the plant, if the flowers are never pruned after they have finished flowering, you may develop a cycle of one "good flowering" year followed by a "bad flowering" year because the plant is trying to recover from producing all those seed pods.

A lilac that is never pruned will often flower poorly, if at all, and will become leggy and sometimes even die out in the middle of the shrub. Lilacs produce suckers readily from the roots, and while in theory you could "renewal" prune it right to the ground, and have suckers sprout from the stump, most people don't go with this route.

Usually lilacs that have reached this stage are quite large, and taking the entire shrub down to a stump would leave a large unattractive hole in the landscape. A better strategy is to take out one-third of the largest stems at ground level each year for three years. By the end of the third year the whole shrub should be renewed, and should be flowering once more.

Another reason to stay on top of pruning your lilac is the lilac borer. This pest burrows under the bark of lilac, and can be devastating. I've seen it very commonly in shrubs that have lots of old thick branches that are growing poorly. Keeping your lilac growing vigorously with young branches is a cultural method to keep this pest at bay. If you have further questions on chemical control, feel free to give our office a call.

Lilacs may also have oyster-shell scale, an insect that looks like brown or grey warts on the stems. It is controlled by pruning out the affected branches, and applying dormant oil spray.

In late summer, I guarantee you someone will call me to ask about why their lilacs leaves look like they have white powder on them. This is a very common fungal disease called powdery mildew. It doesn't hurt the plant at all, it just bothers homeowners. You can reduce the extent of powdery mildew by pruning your lilac to allow good air circulation, but it may still develop. Luckily it doesn't tend to develop until late in the season, about a month short of when the shrubs naturally lose their leaves before winter.

Some newer introductions to the lilac world are reblooming lilacs, which have a large flush of blooms in the spring like other lilacs, a smaller period of bloom in the fall, and sporadic blooms here and there over the summer months. I bought one of the first reblooming cultivars, 'Josee' about ten years ago and have really enjoyed it. It has been around since 1974 and produces more flowers in years that are cooler than average. The blooms are more pink than purple, and the clusters of flowers are a bit smaller than my old fashioned lilac in another part of my yard. It is a dwarf lilac as well, reaching a maximum height of four to six feet. While not as spectacular as my old fashioned lilac, it does rebloom as promised.

A more recent reblooming lilac cultivar is 'Bloomerang®' which also grows to a maximum of four to six feet tall. Though 'Josee' had been around for years without sparking any sort of garden controversy, 'Bloomerang®' ignited a bit of fury on the interwebs probably thanks to the instant nature of blogs and social media. A few garden writers objected to the introduction of this cultivar, arguing that it was just a plant novelty that serious gardeners would reject. To some people, having a lilac blooming at other times of the year is sacrilege. Fortunately or unfortunately depending on your point-of-view, the 'Bloomerang®' lilac surpassed all estimates of demand in its first years on the market and continues to be a popular choice for many gardeners.

No matter whether you are a lilac "purist", preferring a couple of weeks of fleeting blooms each spring from a traditional lilac, or a person that would like to savor a bit of the lilac's intoxicating fragrance all summer long, lilacs are a sure sign that the outdoor season is upon us. It's time to get out in the garden and enjoy our time there!

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