Lilacs are very easy to grow and care for, but they do have a few basic needs that must be met for success. They need full sun – no fewer than 6 hours a day, and 8 or more is preferred. They also require well-drained soil, or in other words, soil that never stays wet or soggy for long periods. This is especially important in winter. Lilacs are fairly adaptable to soil types, though they really thrive in alkaline soils. If you wish to prune lilac, do so immediately after blooming. Lilacs are actually more cold tolerant than they are heat tolerant. In fact, they need a minimum of 1,700 hours of temperatures below 45°F in order to bloom.