Extremely Cold December May Pay Off With Lilac Blooms

Somewhere on your property there has probably been some damage from the ravages of winter. In some cases, it will be very apparent, as with azaleas and rhododendrons that may fail to flower on top but flowered profusely on the bottom—which was insulated by snow cover. On the other hand, there are some plants that were actually helped by the extreme cold back in December.

Among the plants that revel in pipe-bursting winters, none seems to have been more blessed than the lilac (Syringa). This was noticed a number of years ago by my Washington, D.C., clients who had an estate in northwest Virginia, an area with a growing season and hardiness zone remarkably similar to Long Island, except in August. And just about now is when they, and we, would be expecting lilacs to begin blooming. In a “normal” year, that is.

Well, these clients, whom we’ll call the Greens (not to protect the innocent, but my livelihood), were driving out to the country early one May when they came upon a magnificent sight that was described to me as a quarter-mile-long planting of “native” lilacs. The Greens were—how shall I put it—horticulturally challenged.

The fact of the matter is that lilacs are not native to this country: They are an Old World shrub that was first imported to this country in the 1600s. They perform best in hardiness zones 3 to 5, in states such as Massachusetts or the Dakotas—but this has not stopped millions of us from trying our luck in areas where mild winters and hot summers can lessen their magnificence.

Usually, we cannot compare our blossoms to those of our northern friends, who enjoy spectacular displays of scented flowers and heart-shaped foliage.

If lilacs strike your fancy, you may want to travel up to my ancestral city of Rochester, from May 11 to 20, for the 120th annual Lilac Festival in Highland Park. The festival usually draws more than a half million visitors to an area that has a horticultural history rivaling Long Island’s.

There are more than 1,200 bushes that include more than 500 varieties in a park designed by Frederick Law Olmsted. The collection was started in 1892, when horticulturist John Dunbar began the organized plantings from some 20 slips (cuttings) that were thought to be decedents of plants brought to America by early colonists, who may have gotten them from the Balkan mountains.

Then, from June 8 through 17, there’s also the Mackinac Island Lilac Festival in Michigan, if you miss the Rochester show.

But this spring will probably turn out to be a memorable exception for us. Throughout the month of May and into early June, we will see a profusion of purple, blue, reddish and lavender trusses that delight fanciers in Europe. They link the month of May with intensely fragrant varieties that are, unfortunately, hard to find on this side of the Atlantic.

I also should mention white in the list of lilac colors, because the serious lilac grower invariably finds room for at least one shrub with immaculate white (and usually fragrant) blooms. One theory holds that when a white is planted among the purple varieties, the white intensifies the effect of the purple—and it works.

A yellow lilac was developed in the 1940s and named Primrose, but it never gained acceptance in the American market. After all, when someone describes lilac as a color, what do you see? Case closed.

There also are Asian lilacs, and among these there is a dwarf Korean lilac that is also a light yellow, but, again, it is more a novelty than a cherished specimen, though other Korean varieties are very popular now.

The lilac needs several weeks of hard freeze for the optimum bud development that leads to superb blossoms. Lilacs can happily live in temperatures down to minus-40 degrees. On the other hand, a few newer varieties, notably those of some tree lilacs and one Chinese hybrid named Lavender Lady, perform well in states such as Georgia and Alabama … just in case you’re moving. If you try growing common lilac in those states, you end up with no blooms and a good dusting of summer mildew.

Lilacs can make it with less than perfect drainage, but they cannot survive in low-lying areas that invite standing water. For best bloom performance, and to cut down on the inevitable end-of-August mildew attacks, lilacs prefer full sun, good air circulation and soil improved with well-decomposed organic matter. A slope is a good place for them, if you are so fortunate to have one, because of the enhanced drainage, and their roots, which are extensive and virtually indestructible, are good at anchoring soil. (No, sorry, they can’t be used for erosion control on your dune.)

Unfortunately, one of the banes of the lilac, the lilac borer, is undisturbed by harsh winters. The presence of the lilac’s lethal enemy may be detected by holes in the bark at the points of entry and by telltale traces of sawdust on the ground below afflicted branches. Such branches should be cut off at the ground. The borer rarely will kill the plant, and careful observations on your part may enable you to eradicate it in a few years just through preventative pruning.

On the other hand, another pest, called wax scale, is put off by harsh winters. This insect has a waxy white body with a red center and has been compared to jelly doughnuts in miniature. They damage a large number of shrubs, such as hollies, camellias and boxwood. They excrete a sweet, sticky honeydew that attracts ants, and a fungi that results in a blackening of the tops of leaves with something we call “sooty mold.”

These scales usually do not become a serious problem, as the occasional severe winter will control them, but if they do get out of hand, they may be eradicated, or at least controlled, with sprays of horticultural oil early in the spring.

There are probably 25 species of lilacs, and since there have been a great deal of hybridizing and research done on them in this country, in Europe, Korea and China you can find nearly 150 cultivars in single- and double-flowering types, from 2-foot dwarfs to 20-foot shrubs—though 20 feet is pushing the shrub limit.

But, no matter the height, there is the perennial question of how and when to prune lilacs. Obviously, if you prune them in the spring, you remove the flower bud, and you’re bound for a perpetual state of no flowers but wonderful foliage.

Pruning is always done right after flowering. So depending on the variety, this can happen anytime in May or June. Dead wood should always be pruned out whenever it’s noticed. As for the rest of the plant, there is a rule of thumb that calls for the removal of one-third of the old wood each year.

This may be a difficult task for the squeamish, but if you stick to this regime (especially on larger plantings and specimens), by removing a third of the canopy each year, you are opening up the shrub to light and air and removing older wood that tends to flower less vigorously. This also encourages repeated new growth and guarantees that you will never have a spring without these wonderful flowers—and, of course, you’ll keep growing.