This is first and foremost. Lilacs want full sun, at least five to six hours a day during the growing season. Be sure your site will provide this, as less sunlight will give you less blooms, and none at all in shaded areas.
Lilacs absolutely do not like wet feet. Their roots must stay moist, but not sitting in water. The soil must drain properly and allow air around the roots for optimum health. Lilacs are from the mountains, growing out of rocky terrain with little topsoil, which allows for ideal combination of air and water.
The right soil mix will give the proper nutrients and proper drainage and aeration. The soil should be comprised of small pebbles or course sand only, good garden soil, and organic ingredients such as wood chips, sawdust, compost, or straw which has been broken down already, etc. If planting an already large shrub from a container or transplanting, follow these steps:
If planting in clay or hardpan soils, then you must create a raised bed to provide proper drainage, using the same layered process above. Planting in a hole of clay soil, even with the proper ingredients, will most certainly spell doom for your lilac.
Pruning will keep your lilacs in good health and promote good growth, keeping blooms at nose level, and lots of them. Only prune right after blooms are spent. pruning any other time will risk cutting next years flowers. Next year's blooms come from Spring and Summer’s growth this year, with the buds fattening up usually by end of Summer.
Generally, cut out old, leggy growth, the smallest suckers but leaving some for future new main trunks, cut out any diseased stems, and any small twiggy growth, which by the way is a sign of depleted soil conditions.
Following these guidelines will ensure a lifetime of healthy shrubs and plenty of blooms!