Evergreen Agapanthus cultivars are more tender than the deciduous types, and will probably require frost protection in colder regions. Therefore, when temperatures start to drop, consider moving container-grown plants to a sheltered location (such as a greenhouse or south-facing porch), and covering border-grown specimens with a cloche, or double layer of horticultural fleece.
Keep them well-watered during the growing season, applying a balanced liquid fertiliser each month from spring to late summer. Then, in September, gradually ease back on the feeding and watering, allowing the plants foliage to toughen up. By mid-autumn, stop feeding altogether, and only water sparingly throughout the winter.
Grow garden plants in rich fertile soil in a sunny, sheltered position. When growing Agapanthus in patio pots, use a soil based compost such as John Innes No.3.