Lilac trees (syringa reticulata and S. pekinensis), relatives of the olive, are low maintenance, deciduous trees. In the residential landscape, lilac trees provide summer shade and fill the garden with the sweet scent of their blossoms. Lilac trees have deep roots and require good drainage to thrive. Sunshine, adequate air circulation and proper pruning will ensure you of years of beauty from your lilac tree.
Water the lilac tree deeply, once a week while it blooms. A soaker hose, set at the drip-line and left to run for one to two hours, will provide the tree's roots adequate moisture.
Keep the soil weed-free in a 3-foot radius around the lilac tree.
Add a 3-inch layer of mulch, in a 3-foot radius around the tree, keeping it 2 inches from the bark.
Fertilize with a high-phosphorous fertilizer in early spring. Fertilize again with an all-purpose plant food after the blooms have died. Apply the fertilizer at the drip-line, according to package directions, and water well after the application.
Apply lime to the soil around the base of the tree, at the rate recommended on the package, if you live in the Northwest or other areas with acidic soil.
Check the lilac tree for aphids and use insecticidal soap to control infestations.
Remove the mulch in the winter as mice and moles will use it for bedding and have a tendency to gnaw on the base of the tree.
Inspect the lilac tree for signs of powdery mildew, a gray or white substance generally found on the leaves in hot and humid weather. Prune off infected branches and dispose of them. Use a fungicide labeled for control of powdery mildew, according to the instructions on the package.
Remove spent flowers periodically during the season. Use your pruning shears to snip them off just under the base of the flower.
Prune the lilac tree in mid-fall to maintain the desired shape. Cut off any crossing, dead and diseased branches and remove suckers (small shoots at the base of the tree). Don't prune too much or you may prune off next year's flowers.