A deciduous tree, the lilac (Syringa) produces deep green leaves that give way to fragrant blooms in the spring. Lilac trees can grow to 15 feet with a 10-foot spread at maturity, which usually takes about five years. Hardy within USDA planting zones 3 through 7, lilacs will propagate from seed when planted in well-drained sunny soil with a pH between 6.5 and 7.
Select a location for your lilac trees and test the pH of the soil with a soil testing kit. If your soil does not meet the required pH you will need to amend prior to sowing the lilac seeds.
Loosen the soil with a garden fork and amend if necessary. Add lime to the soil if the test reveals a pH below 6.5 or peat moss for a soil pH above 7.0. Add the required amendment per label instructions.
Sow the lilac tree seeds into the soil in the fall, before the winter thaw. Press the seeds into the soil at a depth of 1/16 inch, at a distance of 3 to 6 feet apart. Pat the soil over the seeds to remove air pockets.
Spread a layer of mulch around the lilac tree. A 3-inch layer of bark mulch will protect the seeds over the winter and reduce weed growth in the coming spring.
Water the soil lightly after planting, just enough to moisten the soil. Keep the soil moist, but not wet throughout the germination process using a garden hose. Germination should occur within 30 to 40 days of sowing.
Provide your lilac trees with at least 1 inch of water per week as they grow. Maintain moist soil at a 1-inch depth at all times. Weekly supplemental waterings in addition to rainfall are often necessary until the lilac trees are established.
Prune lilac trees in the fall. Use a pair of sharp pruning shears to remove dead, damaged or inward growing branches. Use your fingertips to pinch off any spent blossoms that are remaining on the lilac tree. Pruning will encourage future growth.
Lilac trees grown in well-amended soil will not need fertilising. Treat mildew or lilac blight with a fungicide. Lilac trees are susceptible to leaf miners, which require treatment with a natural insecticide.
Do not overwater the lilac trees. If the soil feels moist at a 1-inch depth do not add more water. Check the soil again in a few days.