How to Grow Lilac Hedges

Select the type of lilac bushes to plant based on the use and location of the hedge. The compact Palibin lilac (Syringa palibiniana), which grows to just 5 feet high by 7 feet wide, is suitable for separating areas of the garden, such as the vegetable garden and a play area. The larger Henri Robert, with its blue-toned flowers, and white-blossomed Monique Lemoine grow to 12 feet high by 8 feet wide and make a formidable hedge at the end of a vast, sweeping lawn.

Mark the spot where each lilac will be planted with a garden stake pounded into the ground. Allow between 5 and 7 feet between each plant. The spacing for Miss Kim, a perfume-scented lilac that grows up to 8 feet wide, would be 5 feet between plants. Measure 6 to 7 feet between larger lilac bushes, such as the fragrantly spicy Syringa pubescens and the Sensation lilac, which has white edging around each of the tiny purple blossoms in its flower clusters.

Dig holes at least 2 feet deep and twice as wide as the plant's root ball. Separate and spread the roots as you set the lilacs in the holes. Backfill with alternating layers of 2 inches of garden soil and 1 inch of compost. Ensure the base of the plant, where the branches join the roots, is even with ground level.

Water newly planted lilacs until the surrounding ground is soaked. Water the plants deeply whenever the top inch of soil becomes dried out through the first growing season. Thereafter, water established plants during extended dry weather periods. The lilacs may be watered individually or by running a soaker hose the length of the hedge.

Prune lilacs lightly immediately after the blooms fade. Cut the spent flower heads off of branch tips with long-handle pruners. In mature hedges, remove old wood and branches that have died back with a pruning saw.

Examine the lilac hedge monthly for pests and disease. If powdery mildew appears—as it may after a long, humid, cloudy period—contact staff at a local garden center or your county extension agent for the most current fungicide treatment products and appropriate application methods.