Lilac Selection & Pruning

Lilacs are one of the most recognized and best loved shrubs found in Nebraska landscapes. It’s also one example of a plant that performs wonderfully in northern gardens, hardiness zones 3-7 for most species, but lacks vigor and does not flower reliably in southern gardens (Zone 8 and higher).

lilac-4181633_1920Lilacs are easy to grow and tolerate much abuse, particularly common lilac, S. vulgaris. As with most blooming plants, lilacs prefer full sun locations and well drained soil. Plants in shady locations frequently struggle with powdery mildew fungus each year. Old flowers should be cut off as soon as flowers fade to keep plants looking well-groomed. Annual pruning helps to keep plants vigorous and blooming profusely.

Common species of lilacs include the following:

  • Syringa meyer , Meyer Lilac (often called Dwarf Korean lilac) – a dense, neat lilac with a good uniform outline. Violet-purple flowers produced in May are softly fragrant. Literally covered in flowers when blooming. Height 4-7 feet, width 5-6 feet. ‘Palibin’ is a compact form that grows 4-5 feet high and 5-7 feet wide with reddish-purple flower buds that open to whitish-pink flowers.
  • Syringa microphylla , Littleleaf Lilac– smaller leaves result in a finer textured shrub, when compared to S. vulgaris. A handsome, broad-spreading shrub grows 6 feet tall and 9-10 feet wide. Fragrant, rosy-lilac flowers. Works well in a shrub border, groups or as a hedge. ‘Superba’ had single, deep pink flowers and is quite floriferous.
  • Syringa persica , Persian Lilac– a graceful shrub with upright, arching branches reaching 4-8 feet in height and 5-10 feet in width. Dark green foliage and pale lilac, fragrant flowers produced in May. A nice small lilac with a mass of flowers in season.
  • Syringa reticulata, Japanese Tree Lilac– a large shrub or small tree form of lilac reaching a height of 15-20 feet, and width 15 feet. Stiff, spreading branches develop an oval to rounded crown. Creamy, white, fragrant flowers are produced in June. An excellent specimen tree and small enough to plant under utility lines. If allowed to develop into a tree, annual pruning is not necessary.
  • Syringa villosa , Late Lilac– blooms in late May or early June, later than other lilacs. A bushy shrub of dense, rounded habit with stout, stiff upright branches. Many cultivars are available with flower colors including pink, dark purple-red, violet, rosy lilac and white. Not as fragrant as S. vulgaris. Height 6-7 feet, width 6-8 feet.
  • Syringa vulgaris , Common Lilac– the most common form of lilac grown in Nebraska, forms an upright shrub with a height of 8-15 feet and width of 6-15 feet. Blooms in May with extremely fragrant flowers. Well over 400 cultivars are available including a wide range of colors and flower forms.

If you would like to add a lilac to your landscape this year, it’s worth the time to visit the lilac collection at the Yeutter Gardens on the University of Nebraska’s East Campus.  There you can view over 50 cultivars and species of lilacs to consider, while strolling through the gardens with an ice cream cone from the nearby UNL Dairy Store.  The best time for viewing most lilacs in bloom is from late April through mid-May.

Lilac Pruning
Unfortunately, as lilacs mature, the lower portions of the shrub become shaded and usually lose their leaves. As a result, large, overgrown specimens are often leggy and unattractive. Their thick, heavy stems are very attractive to lilac borers. Start young plants on a regular pruning program in the fourth or fifth year of growth as outlined below. Old, neglected lilacs can be renewed or rejuvenated through pruning. Home gardeners can choose between two different pruning methods.

Three-year Plan. The best way to prune lilacs it to initiate a three-year pruning cycle. Begin the procedure the first year by removing one third of the largest, thickest stems at ground level in late winter. For young plants, this may mean you are only remove 2 or 3 stems.

The following year, again in late winter, prune out another third of the thickest stems. Repeat the process again in the third year.

For plants, this method has the advantage of not removing all stems with their stored carbohydrates all at the same time. And it leaves the plant with an ample amount of foliage each year so it can photosynthesis normally, maintaining health and vigor. Since lilac wood needs to be 3 or more years of age before it blooms, this pruning method also allows gardeners to enjoy flowers every spring.

1317042-PPT
A well-pruned lilac shrub. Syringa vulgaris ‘Betsy Ross’ – Margaret Pooler, Bugwood.org.

When properly pruned using the 3-year plan an old, overgrown lilac can be transformed into a vigorous attractive shrub within a few years.

 

 

 

 

 

Renovation Pruning. A more drastic way of renewing an overgrown lilac is to cut the entire plant back to within 6-8 inches of the ground in late winter, March or early April. This severe pruning will induce a large number of shoots to develop during the following growing season.

In late winter of the next year, select among last year’s new shoots and retain several strong, healthy ones to form the shrub framework. Remove all other shoots at ground level. To encourage the development of branching in these young stems more quickly, cut them back at staggered heights just above an outward facing bud.

This method has the disadvantage of removing all flower buds and delaying flower development for about 3 years. But it does allow for the pruning work to be done all at one time. Once rejuvenated, start the 3-year pruning program to keep your lilac beautiful and healthy.

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