Dr. Leonard Perry, Extension Professor
University of Vermont
The unique scent and beautiful flowers of a Lilac are a welcome sign of spring. This relatively care-free shrub is a beautiful addition to nearly any home landscape.
Lilacs are ubiquitous in New England in the spring, great in landscapes as well as cut in vases. They are an historic plant, found around many old homes and even surviving around old foundations after the home has fallen down. They are easy to grow, require little care, have a famous fragrance, and come in variations of red, pink, white, and purple. Even though blooms only last a couple of weeks, with a diversity of different plants from the various species you can have blooms over a 6-week period.
The two main requirements for lilacs to succeed are a well-drained soil and full sun. They will tolerate some shade, but won’t be as dense nor bloom as well. Once established, they will even tolerate dry soils and drought. Make sure when planting you allow plenty of room for the mature size of a lilac (maybe 8 to 15 feet tall and wide), otherwise you may need to “basal prune” all stems back near the ground, and then wait a couple years for new shoots to develop and get a few feet tall.
You should plant lilacs where you can appreciate their informal upright natural shape. Lilacs are often seen near building foundations, and are especially good near corners. They make great specimens in lawns and borders, and planted in a line make a fine seasonal hedge.
If you like the look of neatly rounded shrubs, most lilacs won’t please you, although there are a few exceptions. The single purple Paliban Korean lilac (Syringa meyeri) which grows 4 to 5 feet tall and a bit wider, and the single violet ‘Miss Kim’ Lilac(S. patula). Both have a rounded habit, unlike other lilacs.
Once established, fertilize lilacs lightly each year if at all. In good loamy soils, or with some compost placed around plants, they may need no fertilizer. If fertilizing, do so right after bloom. Too early and flowers may abort with only foliage appearing. Too late and plants may not harden properly for fall. Around the fourth of July is about as late as you should fertilize, or for that matter prune.
Types of lilacs
Most lilacs gardeners are familiar with the common lilacs (S. vulgaris) and their cultivars (cultivated varieties) that bloom in mid to late May in the northern U.S.. Some that bloom just a bit earlier are the hyacinthiflora hybrids, first bred by the famous Lemoine nursery in France in 1876. Examples of these are the single purple ‘Pocahontas Lilac’, the single white ‘Mount Baker’, the single blue ‘Blanche Sweet‘, or the single magenta ‘Asessippi‘.
As you see, lilacs come in more colors than “lilac” and white. Lilac specialists have grouped the over two dozen species and hundreds of cultivars into 7 flower colors: white, violet, blue, lilac, pink, magenta, and purple. For each of these there are singles and doubles. In addition there is the single yellow ‘Primrose’and the bicolor ‘Sensation’. The latter arose as a mutant in a Dutch greenhouse (from the lavender ‘Hugo de Vries’ that was being forced to flower at Christmas) in 1938, and has purple petals each in white.
The other large group are the late lilacs, mainly the Preston hybrids originally bred by a Canadian breeder by that name. These may not have the wonderful fragrance of the common lilacs, but bloom a week or 10 days later and tend to be larger in all respects– leaves, flowers, and wider plants. A few of my Preston favorites are the deep pink ‘Miss Canada‘ and ‘Donald Wyman’, and the white ‘Agnes Smith’.
I often get asked what is my favorite lilac. It is hard to answer as so many, in fact most including the common species, are beautiful. The one that stands out for me and many though is ‘Krasavitsa Moskvy’, or as many know it Beauty of Moscow. It was selected by a famous Russian breeder in 1947 from an offshoot of ‘Belle de Nancy’– one of the French Lemoine hybrids. The pink buds open into creamy white flowers tinged with pink, a silvery opal color.
How to prune a lilac
When it comes to pruning lilacs, experts have a couple of opinions. Some (such as myself) only prune branches as needed, eventually removing about a third of old branches each year. This allows the plant energy to produce new branches. Eventually most lilacs will get very tall, with most of the flowers appearing at the top. This makes the blooms hard to see up close, but fine from home windows, the street, or at a distance. Plus, with some pruning of lower branches you can appreciate the attractive stem architecture.
Others like to prune about a third of new growth off each year, back to sideshoots, not sheared like a hedge. This keeps plants and their flowers lower, but sacrifices the natural shape and effect of the stems. If you need to prune lilac branches that are obstacles, or crossing and rubbing on each other, do so right after bloom.
Lilac pests and diseases
The main problem you may see with lilacs is the white powdery mildew disease on leaves. This will be most common if if your site has late morning dew and little air circulation. Powdery Mildew is more of an aesthetic issue with lilacs and doesn’t cause enough harm to plants to warrant treating. During very wet springs some branches may suddenly wilt, and their tips turn black. This is a blight which should only come once, and new buds should emerge from stems in a few weeks. Occasionally a lilac may get small rounded brown bumps, or scales, which can be treated by cutting off the infected branches.
Dr Leonard Perry is an Extension Professor at the University Of Vermont and an advisor to the Vermont Association Of Professional Horticulturists
Buy lilacs on amazon: ‘Bloomerang Purple’ Lilac – Syringa – Proven Winners
This article originally appeared on Perrys Perennials