The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Delphiniums like moisture and need about 1 inch of water a week. If rain is sparse, soak the soil at their roots to a depth of 10 to 12 inches. Overhead watering weights down their heavy bloom stalks and promotes mildew on their leaves. During hot, dry weather, water thoroughly every 5 to 7 days. For information on products see the file on Choosing Watering Equipment
Delphiniums need fertilizing in the spring when they are planted and later in the summer when they are cut back to induce new growth. Sprinkle a handful of granular all-purpose fertilizer on the soil around each group of delphiniums at these times. Do not allow it to touch the foliage or stem. The next rain will soak it into the soil. For more information see the file for Choosing Fertilizers
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A 1 or 2 inch layer of some organic material like chopped leaves, straw or commercially shredded bark spread over the soil at the base of each delphinium plant helps control weeds, conserves soil moisture, and keeps roots cool during the summer. It is important for winter protection, as well, especially in areas that get little snow. Add evergreen branches, more straw or chopped leaves to help protect the soil from heaving due to fluctuations in winter temperatures. Do not use whole leaves because they mat when wet and prevent water from penetrating into the soil. For more information see the file on Using Mulch
It is important to cut off fading flower spikes before they go to seed. Later, when the foliage turns yellow, cut off the remaining stalks down at the crowns. New shoots will emerge and may provide a bonus blooming in the fall.
Delphiniums need staking to help support their flower-laden hollow, brittle stems. Begin with 4-foot stakes when the plants are about a foot tall. Replace them with taller stakes as the plant grows. Stakes that are taller than the plants look unsightly. Tie the plants to the stakes with soft cord or strips of fabric. For more information see the file Staking Flowers
Although they are perennials, after 2 or 3 years most delphinium plants pass their peak, lose vigor and die out. Replace them with new seedlings from the nursery or plant seeds that are easy to grow. Sow them in the spring or summer, up to 2 months before frost. Cover them with a thin layer of peat moss or sand. They'll germinate in 8 to 15 days. The new plants will flower the next year.