Plant the seeds 1/8 inch deep, sowing two to three seeds per pot.
Set the pots outdoors or in a 60 to 65 degree Fahrenheit room. Avoid locations where the soil freezes or where temperatures rise above 75 degrees Fahrenheit.
Move pots to a full-sun location once the seeds germinate, typically within 20 days of sowing. Move outdoor pots indoors once temperatures drop below 40 degrees Fahrenheit. Maintain a temperature between 70 and 75 F after germination.
Thin the plants once they produce their second set of leaves. Pinch out the smaller and weaker plants in each pot so only one larkspur plant remains in the pot.
Water the larkspur plants when the soil surface begins to dry. Fertilize the plants every two weeks with a balanced fertilizer diluted at the package recommended rate.
Transplant the larkspur flowers outdoors in a well-drained, full sun bed in spring once frost danger has passed. Space the plants 12 to 16 inches apart.
Water the flowers once weekly so the top 6 inches of soil remains moist. Larkspur tolerates some drought but flowers best with consistent soil moisture.