Delphiniums thrive in the cooler climates of the north country, though they will grow as far south as zone 7. The New Millenium hybrids, however, tend to be more tolerant of heat and humidity. They grow best in rich, well-drained soil with a basic pH. If your soil is naturally acidic, adding lime will help to provide these conditions. They are also heavy feeders. The addition of compost or manure to the soil as well the use of granular fertilizer will result in healthier, stronger plants. Delphiniums can be grown in full sun or partial shade, though full sun may help to prevent powdery mildew. When planting, be sure to set the crown at or above soil level to avoid rot. Since their stems are hollow, taller varieties of Delphiniums should be staked to prevent damage from wind and rain. These new hybrids tend to be longer lived than their short-lived cousins but may be propagated from basal cuttings.