The lilac (Syringa spp.) is a woody plant that produces fragrant blooms in the spring which are attractive to bees and butterflies and which make attractive cut flowers. A perennial in U.S. Department of Agriculture plant hardiness zones 2 through 9, depending on species, lilacs come in different colors and varieties. To get the most blooms on a lilac, pruning at the proper time is essential.
Types of Lilacs
As the name implies, common lilacs (Syringa vulgaris, USDA zones 3 to 7) are the most common variety in the U.S. This variety blooms once in late spring -- specific dates differ by region. There are some reblooming varieties like the Josee lilac (Syringa 'Josee,' USDA zones 2 to 9) and the Bloomerang lilac (Syringa x 'Penda,' USDA zones 3 to 7).
For small spaces, dwarf lilacs are ideal. The Dwarf Korean lilac (Syringa meyeri 'Palibin,' USDA zones 3 to 7) is a smaller, denser bush that offers lavender blooms with lilac scent.
With over 1,000 varieties of lilacs available, there are options in many sizes and colors. Read all labels carefully to determine if a certain variety is appropriate for the intended space.
When to Prune
Do all pruning immediately after blooming. For most varieties, this will be in mid to late May. For reblooming varieties, prune after the last blooming cycle of the year.
Lilacs bloom on old-wood, which means they bloom on growth from last year. This is the growth that happened after the last time they bloomed. It is very important to prune immediately after they bloom -- waiting any longer may mean that buds for next year have been removed.
How to Prune Lilacs
Sterilize pruning tools before making cuts. Use an alcohol pad on any saws, loppers or pruning shears used to prune lilacs. Most small cuts can be done with pruning shears. Removing old canes will require the use of loppers or a small hand saw. Unless the lilac is showing signs of disease, like early leaf loss or spots on leaves, it is not necessary to sterilize clippers between cuts.
- Deadheading: Remove spent lilac blooms after they are finished blooming to allow the plant to store energy for next year's blooms. Snip the stem just under the bloom and compost the clippings.
- Shaping: After lilacs have bloomed, remove any oddly-shaped, dead or damaged stems to the closest strong shoot or, on plants with more than 10 canes, remove the entire odd or damaged cane at the ground.
- Rejuvenation: Lilacs over 10 years old often have too many canes and may start blooming less. When that happens, prune for rejuvenation. The first year you notice the lilac needs rejuvenation, after blooming, remove one-third of the oldest canes -- easy to identify because they are the largest -- by cutting them with loppers at the ground. Do the same thing the second year after blooming, and once more the third year. This should take care of all the old canes. Continue to remove the oldest canes every three to five years to keep the lilac producing big, healthy blooms.