Spring has sprung and the phone in our office is ringing off the hook! Spring clean-ups are in full swing, beds are getting a fresh layer of mulch and we are looking forward to planting beautiful landscapes. Several clients have asked this week, “When is the right time to prune lilacs?”
The traditional lilac, Syringa vulgaris, is known for its wonderfully fragrant flowers. A lovely bouquet will easily fill a room with fragrance. Unfortunately that’s their only real ornamental attribute. They tend to look gangly and unkempt most of the year. Throw in a little powdery mildew on the leaves and lilac shrubs leave much to be desired. It’s probably best to tuck a few traditional lilacs into a shrub border or grouping in the landscape. They are definitely not good foundation plants.
The recent estimate is that there are 2000 cultivars of common lilac. Most are in the pink, purple, blue or white range of flower colors with a few creamy yellows. There are a few listed as powdery mildew resistant such as ‘Charles Joly’ (magenta), ‘Madame Lemoine’ (pure white), ‘President Lincoln’ (true blue), ‘Primrose’ (creamy yellow) and ‘Sensation’ (purple and white bicolor).
Because lilacs tend to be long lived in the landscape, they may suffer from poor blooming eventually. The usual causes are:
1. Too shady a site. All lilacs grow and flower best in full sun and well-drained soil.
2. Pruning too late in the season and therefore removing the next year’s flower buds. Common lilacs should be pruned immediately after flowering to keep them vigorous.
3. Shrubs are in need of renewal pruning. Lilacs tend to bloom best on younger branches. Prune by removing about one third of the older branches down to the ground each year after flowering.
4. Poor shrub vigor due to scale or borers. Usually removing the older stems will help to control these insects. Oystershell scale may require a spray of insecticidal soap or summer oil in late May. Be sure to read and follow all label directions.
Although the common or French hybrid lilacs are magnificently fragrant, there are superior lilac species for the landscape. In my opinion these landscape plants do not have quite the heady fragrance of common lilac, they are far better looking shrubs after they flower and tend to be free of powdery mildew. If you don’t have much landscape space, these are better choices.
‘Palibin’ lilac is a neat, tidy shrub at five feet tall. The dark green leaves are smaller than common lilac. It may flower when quite young with pink lavender fragrant flowers. ‘Miss Kim’ lilac is a little larger at six feet. It makes a nice rounded shrub. It flowers a little later than common lilac with blue lavender flowers. The flowers are small but prolific. ‘Miss Kim’ usually develops a nice burgundy fall color, which is non-existent in common lilac.
Littleleaf lilac ‘Superba’ is also about six feet tall and like the other landscape lilacs forms a nice twiggy shrub. It has red buds that open to dark pink. ‘Tinkerbelle’ lilac might be worth growing just for the name. It has pink flowers on a five feet tall shrub. It has nice green heart shaped leaves.
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