Transplant agapanthus plants in spring, before new growth starts. If you live in U.S. Department of Agriculture Hardiness Zones 9 to 11, transplant in fall as well. Prune off any old blooms or flower stalks and any dead foliage to make the move easier.
Choose and prepare a new site in full to partial sun. Use a site with at least 4 feet of space, quick year-round drainage and good air circulation. Dig into a 2-foot-square area of the new site and turn up the top 10 inches of soil. Mix 7 inches of organic compost, leaf mold, humus or well-rotted manure into the natural soil to give the Lily of the Nile loose, fertile soil.
Dig the agapanthus root ball up and transfer it with all roots intact. Plant the root ball in a hole deep and wide enough to contain it in the newly amended soil.
Water the agapanthus with 1/2 gallon of water to settle the soil around the root ball. Spread 2 inches of mulch over the soil in a 2-foot circle to maintain moisture and warmth.