Pruning

Lilacs were brought to America by the earliest settlers and have been very popular landscape shrubs ever since for good reasons. Lilacs are tough, drought tolerant, usually healthy, long-lived, have masses of beautiful flowers and most of them have a delicious fragrance. In dry Colorado air, you have to stick your nose in most flowers to get the smell, but lilacs carry their rich perfume for quite a distance. Like most young boys, I was more interested in bugs than flowers, but my earliest memory of a flower was lying on a grassy hill next to a lilac hedge in full bloom, soothing my spring fever in the sweet, heady fragrance of the common lilac. This powerful aroma is one of the main attractions to lilac and one of the reasons why people forgive other garden qualities like the huge size and habit of suckering.

In fact, the tendency to sucker and the ease of transplanting are primary reasons for the rapid spread of lilacs across America. By the 1650s, lilacs were growing all over the colonies, and later they were carried west by the pioneers. I recently pruned some lilacs that were planted by miners in the rocky foothills above Boulder. I can just imagine some rough traveler, burning with gold fever and the Colorado sun, sharing his canteen with a lilac sucker.

Lilacs are natives of colder regions of southeastern Europe and northern regions of China and Korea. What we call Common Lilac, Syringa vulgaris, came from Romania, Yugoslavia and Bulgaria. The species comes in purple and white, is long blooming and is one of the most fragrant. It will grow to 12—15′ and can spread to make wide clumps, making a good screen. Because they are native to limestone areas, they prosper in our alkaline soils. And their hardiness makes them enduring in Colorado: books say to zone 4, but local growers say zone 3 or even 2 and to 10,000′.

Another reason lilacs are so popular is that they have been hybridized so much that there are many colors and forms to choose from. From Syringa vulgaris were bred at least 1500 cultivars. Starting in the 1880s, Victor Lemoine of France began selecting and hybridizing lilacs. It was a family enterprise with Victor as the leader, Madame Lemoine climbing ladders to do the actual cross pollinating and their son Emile taking over the business. They achieved 214 successful varieties, and both Victor and Madame Lemoine have great lilacs names after them. These are what we now call the French Lilacs. Since Lemoine, there have been many lilac breeders, several from the United States including Father John Fiala who wrote the great reference Lilacs: The Genus Syringa.

Some successful Syringa vulgaris cultivars available in our area are: ‘Albert Holden’ has deep violet blossoms with a silver reverse and good fragrance and grows to only 7—8′. ‘Arch McKean’ which has magenta flowers and very little suckering, growing to 7—8′. ‘Beauty of Moscow’ (‘Krasavitsa Moskvy’) with double white fragrant blossoms growing to 10—12′.(“one of the finest lilacs in commerce.” Fiala); ‘President Grevy’ has excellent double blue flowers in immense panicles.

‘Edith Cavell’ is rated “excellent” with double white, very showy flowers. ‘Monge’ is a single deep purple that is “outstandingly showy” and grows to 10—12′. This one is thriving at the neglected Cheyenne Station. ‘Sensation’ is very striking with its purple flowers edged with white. ‘Marie Frances’ has true soft pink flowers that are very fragrant.

Besides Syringa vulgaris, there are 22 other species, all from Asia. Some of these are not garden worthy, several were used in breeding great new hybrids and some make good shrubs in themselves. Syringa laciniata is sometimes available. It is quite beautiful with its cut leaves and its lavender blossoms. It is an annual bloomer, is long-flowering and suckers very little.

Syringa meyeri is compact and the variety ‘Palabin’ is available locally. It grows to 5′, needs little pruning and likes loose soils. It has deep purple buds and lavender-blue flowers and succeeds in dry conditions.

Syringa microphylla ‘Superba’ has small leaves, as its name implies. It is slow growing to 6—8′ and is wide spreading with small clusters of dark pink flowers that are sweetly fragrant. This is a lilac that will make a few blooms again in summer and fall. This is a real treat.

Syringa oblata is occasionally available and although it is an early bloomer, it is less susceptible to freezing than S. vulgaris and so is fairly reliable. The flowers are pale purple and the fall color is wine red. The variety dilatata is a superior form with very fragrant purple flowers and the variety ‘Cheyenne’ is extremely fragrant.

Syringa x hyacinthiflora is a cross between Syringa oblata and S. vulgaris. These hybrids bloom a week to 10 days before the French Vulgaris Hybrids. The fragrant flowers can be white, lavender or purple and the fall color is wine red. They are successful large, dense shrubs for Colorado, growing to 10—12′, and can be used as hedges since their leaves and flowers form all the way to the lower branches. They are hardy to 9000′. However since they bloom early, avoid planting them in a frost pocket or next to a tall wall or house where the flowers can be coaxed to open early only to be frozen. A few that are available locally are ‘Mount Baker’ with very fragrant, pure white flowers, ‘Assissippi’ which is the earliest with fragrant lavender flowers, and ‘Pocahontas’ with deep violet fragrant flowers.

Syringa patula is a late blooming species from the mountains of South Korea. The selection ‘Miss Kim’ is fabulous for its compact form and its very fragrant ice-blue-lavender flowers. It has burgundy fall color and prefers a well-drained soil.

Syringa x prestoniae are a series of hybrids from crossing Syringa villosa and S. reflexa. Isabella Preston was the Canadian hybridizer of these prolific bloomers. They flower about 10-14 days later than S. vulgaris and have a spicy “oriental” fragrance. They are very hardy to zone 2 and can grow to 9000′ or 10,000′. They do not sucker and so can be pruned into small multi-stemmed trees. Some varieties that are available locally are: ‘Isabella’ with lavender flowers, ‘James Macfarlane’ with pink flowers, ‘Miss Canada’ with deep pink flowers only growing to 6—9′ and ‘Minuet’ with purple flowers growing to 6—9′.

Another lilac species that is a favorite in Colorado is Syringa reticulata, the Japanese Tree Lilac. It grows to 15—5′, blooming with white flowers in very late spring. The variety ‘Ivory Silk’ has a more compact form and the same cinnamon-brown peeling bark. The fragrance is like privet, that is, not delicious. It is hardy to zone 4 and 6500′.

The best culture for lilacs is fertile, well-drained soil with plenty of organic matter in full sun. The Common Purple and Common White seem to do just fine in my lean gravelly soil with almost no organic matter, but for the hybrids, for longer bloom, bigger and more flowers higher fertility is necessary. Father Fiala says commercial fertilizer is no substitute for two year old manure and compost, because they provide tilth, hold moisture and feed the soil microorganisms. The worst conditions for lilacs are “wet feet”, shade and subsoil. If heavy wet clay is all there is, Father Fiala says to build a 3′ high mound with gravel, top soil, manure and compost; and plant at the top of the mound. Another option is to plant near the top of a slope; never near the bottom. Syringa vulgaris and its offspring are the most tolerant lilacs for heavy clay, but not if it is soggy.

The best pruning for lilacs is to remove the dead, broken and very old. Also take out many of the suckers, but leave the biggest ones if they aren’t too crowded. Once the shrub is mature, remove a fourth to a third of the oldest wood every year. And prune the tallest branches down 10%-20% to a side branch leading out. This should be done soon after blooming so next year’s buds are not removed.

When a lilac has not been blooming well or has gotten very old with little care, it can often be rejuvenated if the roots are sound. First scratch in some composted manure into the top 2″ of the soil, and then mulch 3″ deep. Then cut out the oldest canes, or if it has too much dead, cut the whole shrub to the ground in the early spring before it leafs out. This will either renew it or if the roots are rotten, it may not survive the operation. Do not cut a weak lilac to the ground in the summer, because that would likely kill it.

There is not universal agreement as to the value of dead-heading the spent flowers, but Father Fiala and the Arnold Arboretum believe it is worth the trouble if it is done immediately after blooming. This will save energy that will result in better blooming and health. This can be a big job, but I have found removing even half the spent flowers is helpful.

Lilacs are generally healthy if they get decent drainage, some pruning and some organic matter. But they can have a few problems. In Colorado, a warm February and March followed by a frigid April or May can freeze the buds or flowers and ruin the floral show for a whole year. Another problem can be powdery mildew, turning the leaves almost white. If the plant is strong, this will cause no real harm; just rake up the diseased leaves. Some varieties like Syringa meyeri, S. microphylla, S. reticulata, ‘Mme. Lemoine’ and ‘Pocahontas’ are resistant to mildew. You can control the mildew with a non-toxic spray of horticultural oil and baking soda, one tablespoon each in a gallon of water, or there is a new product related to baking soda called Green Cure. One other possible problem is lilac borer which can tunnel into the wood to weaken or kill stems. This should not be a problem if the plant has good vitality. I have heard “painting” the lower trunks with wood ash and water repels them.

Like every plant, lilac has its strengths and weaknesses, but far more strengths. It is truly a sustainable shrub for Colorado, being both tough and drought tolerant. Enjoy the great variety of forms, flower colors and fragrances. And by planting the early, middle and late bloomers, you can enjoy a long season of flowers. I recommend that you go to the nurseries in the spring when they are in bloom so you can smell and see, and cultivate those that really speak to you. No nursery can carry more than a fraction of even the best varieties. Two mail order lilac nurseries are Heard Gardens in Iowa and Wedge Nursery in Minnesota.

Here are a few Father Fiala identifies as some of the top varieties that are not available locally, as far as I know: ‘Flower City’, ‘Dwight D. Eisenhower’, ‘Avalanche’, ‘Violetta’, ‘Blue Danube’, ‘Mechta’, ‘Larksong’, ‘Marechal Foch’, ‘Paul Thirion’, ‘Edith Braun’, ‘Sarah Sands’, ‘Etna’.