Larkspur is a cool season annual that can add green to an otherwise dreary winter garden and then show off its beautiful blue, lavender, pink, rose or white blossoms in early spring. The flowers are usually blue and appear on a spike that can grow one to two feet high, although some varieties grow as high as four feet. All parts of the larkspur plant are poisonous.
Larkspur is planted in the early spring. It will not germinate if the seeds do not go through a frost. Larkspur is difficult to transplant successfully so should be planted from seed where you want it to grow.
Larkspur will grow best in full sun but will also grow in partial shade, with morning sun and afternoon shade. It needs a well drained place to grow as it does not like wet feet.
Prepare the area you are sowing the larkspur by tilling it to a depth of six inches. Add three inches of compost and till that in. Now you are ready to plant your seeds.
Seed Larkspur four inches apart in groups of ten to twenty plants. Sow the seed on the surface of the soil and press it into the soil. Do not cover it with dirt as it needs light to germinate. It takes about a week to germinate and must be kept moist during that time. Seeds do not germinate well if the soil temperature is above 65 degrees.
Larkspur grows fast and requires a lot of water. Water at least once a week and give the plants an inch of water at a time. If there is a drought or the temperatures are very high, water as frequently as three times a week. However, take care to keep the soil moist and not soggy or the roots will rot.
When the seedlings have two true leaves, thin them to about six inches apart. At this density, they help support each other. Some larkspur grow so heavy with blooms that you must stake the plant to hold it upright. This is more common with the varieties that grow four feet in height.
Larkspur is a cool weather plant. It will generally die when the temperature reaches eighty degrees for any length of time. However, in cooler climates it will bloom and grow until the first frost, when it will die.
Larkspur is self seeding is allowed to develop seeds from its blossoms. It will come back in the same place over and over. It will also spread, so may have to be thinned when it comes up in a part of the flower bed it isn’t supposed to be in. To allow larkspur to self seed, you must not deadhead all of the plants. You will need to let a few get brown and go to seed. You can also save the seed for approximately six months and plant it yourself the next spring. Older larkspur seed does not germinate well, with as low a germination rate as 50%.