Space bulbs 6 to 10 feet apart and bury them 5 to 8 inches deep when planting to allow adequate room for growth. A mature rainbow butterfly bush can span 6 to 8 feet wide. Plant the bush in garden areas that receive full sun to partial shade with well-draining soil. Fertilizer is not needed the first year, but you should add it in subsequent years to promote growth.
The rainbow butterfly bush blooms from midsummer into fall with small, multicolor flowers. The orange, lavender and yellow buds cover the ends of each stem in the bush for lush, continuous color and fragrance throughout the blooming season. The flowering portion of the stem can span up to 10 inches.
The bush requires pruning in early spring to promote blooming. When the new growth appears, prune the old growth back to the base to allow room for the new stems to develop. In late winter, trim the bush just above ground level. This bush grows and spreads rapidly, so trim the dead flowers immediately to prevent the spread of seeds if you want to contain the plant to a smaller area.
The rainbow butterfly bush grows 6 to 8 feet tall in USDA hardiness zones 5 to 9 with dark green stems and leaves up to 10 inches long. This perennial bush attracts many varieties of butterflies, but is not attractive to deer. Few pests plague the bush, but drought or other stress on the plant can allow spider mites to infest the bush.