Do Delphiniums Grow Well in North Carolina?

Climate Requirements

• In the mountains of western North Carolina and the central region of the state, USDA hardiness zones range from 6 through 7, ideal for growing delphiniums as perennials. After the summer flowering period, the plants die back to the ground, going dormant through the winter and reemerging in the spring. In the coastal and eastern parts of the state, where USDA zones include 8a and 8b, delphiniums bloom in late spring and then die out during the heat of summer.

Planting Delphiniums

• Delphiniums grow best part to full sun and moist, loamy soil. Before planting, amend the soil by digging 4 inches of compost into the top 15 inches of the soil. Plant delphiniums from starts after the last frost date, commonly late March to mid-April in North Carolina. When planting, position delphiniums in the planting hole so that the base of the stalk is level with the soil line. Space multiple plants 2 to 3 feet apart.

Growing Season Care

• Water delphiniums regularly, especially through the summer when conditions are dry. Delphiniums need 1 inch of water per week and consistently moist soil. Feed using a balanced fertilizer applied every two to three weeks from spring through fall. Mix liquid fertilizer at a rate of 1 ounce in 2 gallons of water for each 20 square feet of garden bed around your delphiniums. To keep delphiniums from breaking, place a 6-foot-tall dowel or stake next to each plant and loosely tie the flower stalk to it. Keep an eye out for slugs and snails, and pull off any you find by hand.

Cutting Back Delphiniums

• After the delphinium flowers die back in midsummer, cut the flowering stalk 2 inches above the soil line. In North Carolina's USDA zone 7 and cooler areas, this encourages a second flush of flowers later in the summer. After the second set of flowers bloom, delphiniums are done for the season. Wait until winter frosts kill off the growing parts, and then cut back the leaves and stalks 1 to 2 inches above the roots.

Fall and Winter Care

• Overwinter delphiniums by covering the area over the roots with a 4-inch-deep layer of mulch. This insulates the soil and minimizes root disruption from frost heave. In spring, pull back the mulch layer to make room for new growth. In warm coastal regions, delphiniums are done growing after the first early set of flowers. Remove the plants by digging them up by the roots as soon as the flowers fade, and plan to replace them the following spring.