Lilacs (Syringa vulgaris) are among the first flowering shrubs to bloom in many areas in mid-spring, filling the air with a rich sweet fragrance and pleasing the eye with colors that range from white to pink, red, yellow and lavender. Hardy in U.S. Department of Agriculture plant hardiness zones 3 to 7, lilacs can be planted in the spring or fall in most areas, and they're relatively maintenance-free once established. Lilacs can be planted singly or in rows as a privacy screen.
Young lilac shrubs are generally sold as container-grown greenhouse specimens or as bare-root field-grown seedlings. Plant potted lilacs in the spring after the last frost when the soil is workable, or in the fall before the first frost of the season. Keep the soil in the pots moist but not saturated until you are ready to transplant the lilacs. The University of New Hampshire Cooperative Extension recommends planting bare-root stock in the spring, and keeping the roots in a pail of lukewarm water until you are ready to set them into the soil.
Lilacs require full sunlight to thrive and bloom profusely, which translates to at least six hours of direct sunlight per day. They tolerate some afternoon shade, and it may actually benefit the plant during a hot dry summer. In the spring, choose a well-drained area where the soil has warmed to at least 50 degrees Fahrenheit. For fall planting, select a site that will receive plenty of sunshine during the day, with protection from high winds. A southern or southeasterly facing location maximizes the available sunshine during the late fall and winter months.
Soil Preparation and Planting
Lilacs do well in all types of soil, and best in moderately rich soil that registers a pH between 6.5 and 7.0, which is slightly acidic to neutral. To test for pH, perform a soil test using a kit purchased at a garden center, or send a sample to your county extension service or a testing lab. At planting time, dig the hole as deep as the lilac's root ball and three times as wide, which allows you to position the roots without disrupting them. The Clemson Cooperative Extension recommends enriching poor soil at planting time with a 1- to 2-inch layer of compost mixed in at the bottom of the hole. Mulch the area under the lilac bush with 2 to 3 inches of organic material such as shredded leaves, compost or straw to retain moisture and discourage weeds.
Culture and Maintenance
Water lilacs when the weekly rainfall amount is less than 1 inch, and water to a depth of at least an inch. You can visually gauge the moisture level while watering by digging a small hole about 2 inches deep a few inches from the base of the plant. Lilacs generally begin flowering between three to five years after planting, and may benefit from a single application of 5-10-10 fertilizer in early spring or mid- or late October, at a rate of 1/2 pound per 25 square feet of soil. Overfertilizing lilacs has been known to result in excess vegetation but poor blooming. Encourage flowering by pruning off all flowers as soon they've faded. Avoid pruning beyond that point to allow new buds to develop for the following year. Be sure to sterilize all pruning tools before and after use.