Butterfly bush, known botanically as Cassia bicapsularis, is a late fall or early winter flowering evergreen shrub or small tree. It reaches up to 10 feet in height at maturity and is named for the appearance of its flowers that look like yellow butterflies. It is a semi-tropical plant hardy in USDA Zones 9 through 11 and thrives in full sun or partial shade settings. Though it is low maintenance and readily adaptable to a range of environmental conditions, butterfly bush will perform best when its preferred soil conditions are met.
Soil pH Range
Cassia bicapsularis prefers soil with a roughly neutral pH fixed near 7.0 pH or just either side of neutral being slightly acidic or slightly alkaline. Amend very acidic or very alkaline sois to bring them back near the desired range for best performance.
Soil Texture & Drainage
Butterfly bush grows best in nutrient rich soils. It will readily adapt to either light clay, loam or sandy soils provided the soil is easy draining and water does not pool around the roots as this threaten suffocation and root rot. Heavy clay soils should be amended with organic material and sharp sand to improve drainage of water through the soil.
Butterfly bush requires sufficient organic or other absorbent material in the planting soil to hold on to and store enough moisture to see the plant through periods between irrigation sessions, rain or light drought. Amending soil with compost, aged manure and/or sphagnum peat moss will aid the natural found soil in holding moisture but will not block the flow of excess water through the soil.