Choosing a lilac
It is best to choose a plant that already has several branches. Lilacs sold in containers should have well-developed root systems. If you buy a balled and burlapped plant, it should be firmly tied up. Home gardeners may find it more difficult to grow bare-rooted plants purchased in spring.
Home gardeners tend to use division and layering for propagating lilacs, whereas nursery growers mostly use cuttings and even in vitro culture to grow large quantities of plants. Grafting is becoming increasingly less common.
Spring is the ideal time for planting a lilac, in April or May. This will give the shrub plenty of time to develop new roots and store sufficient nutrients before winter. With the increasing popularity of container-grown plants, however, lilacs can now be planted all summer long and even in fall, as late as mid-October (before the ground freezes).
Lilacs should be planted in well drained soil with a neutral to slightly alkaline pH. Heavy clay soil should first be amended with compost or composted manure. Poorly drained clay soils can also be amended by adding sandy loam. If there is insufficient drainage, you can build raised beds.
For the best flowers, choose a sunny site (at least 6 hours of sun a day). Fertilize with a product high in phosphorus and potassium in early May. Avoid using fertilizers high in nitrogen, which encourages leafy growth at the expense of blooms.