Lily of the Nile or agapanthus (Agapanthus africanus and hybrids with this species) is a blue-flowered perennial that grows from a rhizome (fleshy root). Each rhizome sends up several shoots. Rhizomes also reproduce, so over time, a one-gallon plant of a vigorous cultivar like ‘Blue Storm’ will make a clump 2.5 feet wide. One of my large-leaved, unnamed cultivars has spread 3.5 feet in all directions.
Agapanthus is well suited for loamy or clay soils of South Carolina. Add composted organic matter to clay soil before planting. Although agapanthus is drought tolerant, they don’t bloom well if planted in low-nutrient sandy soil.
Some agapanthus cultivars can be a bit finicky about blooming. Not every plant in a clump will bloom. Shoots must reach a certain size before they are ready to flower. To bloom regularly, fertilize agapanthus twice a year, either after blooming, in early fall (September in the Upstate, October in the Lowcountry), or in early spring (early March in the Lowcountry and April Upstate). A low-nitrogen, complete fertilizer that includes phosphorus is best, such as 5-10-15 or 8-8-8.
It’s time to divide and transplant lily of the Nile when clumps don’t flower even after fertilizing. Since agapanthus flowers in June (Lowcountry) to July (Upstate), early fall is the best time to disturb clumps. The long, thick, white roots that stretch out a foot from the rhizome make agapanthus drought tolerant but tricky to transplant. To move a portion of a clump, dig as large a root ball as possible. Don’t cut off bare roots that stick out beyond the root ball; carry them along to the new site. These long roots tend to grow near the soil surface, but it’s fine to cover them with an inch of soil.
For more information, see HGIC 1156, Summer and Fall Flowering Bulbs.