When to Plant Delphinium Seeds

Plant your delphinium seeds directly in flower beds in early summer.

Where to Plant Delphinium Seeds

Cultivate delphiniums in well-drained, moist soil under full sunlight. To address challenges with wet winter soil, enhance drainage by incorporating grit like sand into the planting hole, especially if dealing with heavy soil.

Delphinium plants like full sun to partial shade, and they will grow very quickly. They thrive in average soil and cool weather. When choosing a location, keep in mind delphinium is potentially toxic if consumed.

How to Plant Delphinium Seeds

While not required, delphinium seeds can benefit from a special one to two week treatment called cold moist stratification prior to planting them.

Delphinium is notoriously difficult to transplant, so it is best to sow seeds directly into your flower garden after all danger of frost. When the soil is about 70°F to 75°F, sow your seeds and cover them lightly with 1/8th inch of soil. Space your seeds four inches apart, and after germination, thin seedlings to 10 to 12 inches apart. Keep the soil moist to feed your delphinium’s fast growth.

How to Care for Delphinium

Once started, cosmoses require virtually no attention. You can add a general purpose fertilizer once or twice a season. If a plant grows very tall and is not planted in a wind protected area, it may require staking. If you want blooms all summer long, dead head the old blooms.