Include larkspur in your flower garden and the tall, stately spikes will produce blooms in shades of purple, blue, rose, pink and white all summer long. Most strains are tall enough to be a backdrop for other flowers, and they're especially beautiful planted along a wall or a garden fence. Small varieties are compact enough to make a colorful border plant. Clip a few for a fresh floral arrangement or dry them for a cheery winter bouquet.
Stake larkspur to prevent it from breaking in the event of a strong wind. Some larkspurs can grow to a height of 5 feet or more, and although the stalks are sturdy, the blooms are heavy and can cause the plant to lean and break. The easiest way to stake a tall plant like larkspur is to insert a wooden stake into the soil about 3 inches from the larkspur's stem. Tie the stem to the stake loosely with soft twine or a strip of pantyhose.
Water larkspur twice a week, and more during dry periods, and give it an all purpose fertilizer every other week. Just before the larkspur begins to bloom, give it a high potassium fertilizer. Check the instructions on the package label for amounts.
Cut the blooms for cut flower arrangements just before they reach full bloom. Use garden shears or sturdy scissors to cut long stems to arrange in a vase. Don't worry about removing too much stem from the plant, as pruning will encourage more blooms. Deadheading any spent blossoms will allow the plant’s energy to go into developing new larkspur flowers. To deadhead, just clip the stem below the spent blossom, or pinch it off with your fingers.
Watch the larkspur for signs of problems. Although larkspur isn’t prone to insect problems, it can develop mildew, which is a type of fungus that can be recognized by white or black spots on either side of the leaves, or by a powdery, stringy substance. If the problem persists, the leaves will become distorted, or will turn brown or yellow and will eventually fall off. Treat the infected plant immediately with a fungicide, following the directions on the label carefully.To avoid mildew, make sure the plant has good air circulation and adequate sunlight.