Delphinium is a tough perennial bloomer with colourful blooms on tall, sturdy stems. A versatile plant, delphinium is available in single or double types, in shades of blue, pink, violet, red and white and heights of 2 to 6 feet, depending on the variety. With proper care, delphinium will put on a show in early summer and return for a repeat performance in late summer or early autumn. Delphinium is suitable for planting in U.S. Department of Agriculture hardiness zones 2 to 7.
- Skill level:
Things you need
- Thin bamboo, wood or metal stake
- Soft garden ties or strips of old nylon pantyhose
- Compost or mulch
- Balanced granular fertiliser
- Garden pruners
Plant delphinium in well-drained soil amended with 1 to 3 inches of compost. Delphinium likes plenty of bright sunlight but benefits from afternoon shade in hot, dry climates. Provide air circulation by allowing 1 to 3 feet between each plant, as delphinium is prone to fungal problems in humid conditions.
Stake tall delphinium varieties at planting time or early in the season to provide support, as tall varieties become top heavy and may blow over in a strong wind. To stake delphinium, drive a thin bamboo, wood or metal stake into the ground 4 to 6 inches from the base of the plant. Tie the stem loosely to the stake, using soft garden ties or strips of old nylon pantyhose. Use a stake tall enough to reach the mature height of the plant.
Water delphinium regularly during dry periods. Water the plant deeply enough to saturate the root zone, as deep waterings develop strong roots. Allow the soil to dry slightly between waterings, but never allow soil to become bone dry. A 3- to 4-inch layer of compost or mulch, such as pine needles or shredded bark, keeps the soil cool and moist.
Spread a balanced granular fertiliser around each plant in early spring, then repeat after the first flush of flowers fade in midsummer. Refer to the container label for specific rates of application. Don't allow fertiliser to contact the leaves, and always water delphinium immediately after applying fertiliser.
Remove wilted delphinium blooms and stems after each bloom wilts. Removing blooms as they wilt in early summer or midsummer promotes another flush of blooms in late summer or early autumn.
Cut the plants back to within 2 to 3 inches of ground level after the first hard frost in autumn. Apply a fresh layer of mulch or compost to protect the roots from winter freezes and thaws.
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- Iowa State University Extension; Delphiniums; Sherry Rindels; December 2004
- Colorado State University Extension; Delphinium: The Diva of the Colorado Garden;Terry Deem-Reilly; 2010
- National Gardening Association: Delphinium
- North Carolina State University Extension; Delphinium; Alice B. Russel, et al.
- Utah State University Extension; Delphiniums Are Pretty Tough - One Of The Hardiest Perennials In Northern Utah Gardens; Dennis Hinkamp