Fragrant, flowering lilacs are familiar harbingers of the coming summertime throughout the world's temperate zones. Though lilacs are commonly associated with gardens in the eastern United States, their requirement for excellent drainage in a neutral to slightly alkaline soil makes them especially appropriate candidates for many gardens in the western part of the country too. Heat-tolerant Persian lilacs expand the lilac-growing range, thriving not only wherever common lilacs have adapted but also in warmer climes.