The common lilac, Syringa vulgaris, is a deciduous shrub with a moderate growth rate and fragrant clusters of columnar flowers. Common lilacs are hardy in zones 3b through 7, where extreme heat is not an issue. To the delight of southern gardeners, lilac breeders have developed several cultivars of common lilac that are better able to withstand warmer temperatures than their tender cousins. Syringa vulgaris “Mme Lemoine” and Syringa patula “Miss Kim” are two examples of lilac crossbreeds that thrive in the warm soils of zone 9.
Scout out a location that receives at least six hours of daily sunlight. The site should contain well-drained soil with a neutral pH (7.0). Zone 9 soils contain fluctuating pH levels. If you are unsure of your soil’s pH, test it with a soil testing kit purchased from a garden center.
Turn over the soil with a pitchfork to create a fine planting medium. Modify your zone 9 soil if it is not within the preferred range. Mix peat moss in with the soil if the pH hovers above 7.0 or add lime to soil with a pH below neutral. Add the amendments according to the manufacturer’s recommendations.
Prepare planting holes for the lilac bushes in the early spring, just after the final frost of winter, which usually comes between January 30 and February 30. Dig each hole twice the width of the lilacs’ root-balls and just as deep. Space the holes between 5 and 15 feet apart.
Slip each lilac bush out of its nursery container and set one bush in the middle of each hole. Backfill the holes and pack the soil around the main stem of each lilac bush. Pat the top of the soil after backfilling to remove trapped air.
Run a soaker hose around the lilac bushes and water deeply to a 1-inch depth. Maintain this moisture depth for the first growing season. Zone 9 lilacs require 1 inch of water every week, whether it is through rain, supplemental watering or both.
Prune the lilac bushes to keep them looking neat and tidy. The best time to trim zone 9 lilacs is immediately after blooming in the late spring. Trim damaged, diseased and old wood with a pair of pruning shears. Avoid removing more than one-third of a lilac bush during a single pruning.