The African lily (Agapanthus africanus) actually is native to South Africa where seasonal summer fires occur. This clump-forming evergreen perennial bears dark green, strappy leaves and 2-foot-tall flower stalks in mid to late summer. The flower cluster is a round umbel with deep blue flowers that are tiny trumpets in shape. This species is not overly tolerant of cold, so it's best planted outdoors in U.S. Department of Agriculture plant hardiness zones nine through 11. Sandy loam soils prove best for this somewhat difficult-to-grow species.
Basic Soil Requirements
The African lily grows best in fertile, well-drained sandy soils that are moist from fall to spring. A sandy loam soil -- a soil type that retains moisture and is fertile with equal parts sand and organic particles -- makes the best garden soil for this perennial. Avoid heavy textured and alkaline soils, because it inhibits uptake of some basic trace soil nutrients, but any acidic to neutral soil, pH 5 to 7.2, suffices. According to Richard Jamieson of the Centre for Home Gardening at Kirstenbosch in South Africa, this species is best grown in a rockery.
Gardeners still successfully grow African lily in loamy soil landscapes, especially if a little work is done to improve the soil prior to planting. Dig and overturn soil to a depth of 12 inches with a spade. In dry sandy soils, add organic matter such as compost, rotted manure and leaf mould to improve retention of water and bolster fertility. Avoid planting in heavy clay soils, and adding sand and grit to clay soils doesn't improve soil conditions for the African lily roots.
The African lily does not grow well in soggy, waterlogged soils or bone dry ground. All soils should remain evenly moist from November to May in the southern United States. It is naturally adapted to a hot, sunny and dry summer. Garden soils comprised of sand or on a hillside will dry out more quickly that ones with loam parent materials. Water and liquid feed the African lily freely in early to mid-spring when the plant is actively growing and again once flower stalks appear.
Numerous other species of Agapanthus are commonly grown in gardens across USDA zones seven and warmer. Agapanthus praecox and Agapanthus campanulatus are much more forgiving garden subjects. Their relative ease of culture and wider tolerance of winter cold and clay soils is in stark contrast to that of Agapanthus africanus. Verify you indeed have this species and not another, or a hybrid cultivar.