To start growing larkspur, pick a spot of soil with full sunlight or partial shade. Most people grow it along a fence, use it for borders, or plant it in drifts. The soil should be average to rich and also well-draining. Larkspur requires a lot of water, but soggy soil will cause it to rot - if you have an especially dry period, water them two to three times per week. If you live in a colder area, you can plant in early spring; otherwise it is best to plant in the fall, usually October or November. Since seedlings don’t transplant well it is best to sow the seeds directly in the ground. Follow the directions on the package, which usually instruct to cover the seeds lightly, and is the correct way to plant. The seeds must be close to the surface, because to germinate they need a lot of sunlight. Thus it is best to only scratch them into the soil. Four inches apart is generally enough space, and do not put a lot of mulch on them. During winter larkspur, develop their root systems, and the next spring they go into a blossoming frenzy. If you need to add fertilizer to your soil, do so about once a month, but not after the larkspur have bloomed.
For optimum growth, it is best to group them into sections of 10 or 20 plants. It will take about a week for the seeds to germinate, so be sure to keep them moist during this time. Wait until about two leaves appear on each plant and then thin them out to six inches apart. If excessive heat causes any plants to wilt, simply pluck them out and discard.
Larkspur generally grows best in cooler weather. When the temperature rises to 80 degrees and higher, they will most likely die. But in general, it will grow fast with little maintenance until the first frost hits. As with most annual plants, frost will wipe them out. Remember to keep the soil watered well to feed their fast growth. Also strong winds will damage them, so make sure they are well-shielded. If your larkspur grows too tall, it may have to be staked up since the blossoms will get too heavy. But if they are planted about six inches apart, they will support one another and won’t require staking. Larkspur usually blooms very early in the spring, before any other plants.
It is possible to start larkspur indoors and then transplant in the early part of the spring, but most often they’ll go into transplant shock. If you decide to risk it and transplant anyway, it is a good idea to use peat pots (the brown kind you bury with the plant). This cuts down on transplant shock.
If you want cut flowers for vases, you should wait until about half of the flowers have fully opened before cutting, just before the blooms reach full maturity. If you want to dry out your larkspur, simply hang it upside down in a dark dry place with plenty of air circulation. It is great used in arrangements with other flowers, or simply by themselves.
Be aware that all parts of larkspur, even the seeds, are highly toxic and hence poisonous to many animals, especially cattle. Ranchers occasionally have problems moving herds to locations where larkspur grows wildly. The cattle will eat the larkspur and it will kill them.
Sclerotium rot is the most common disease you will have to worry about with larkspur. It makes the plants wilt and turns the leaves yellow. If you notice your plants infected with it, immediately use a common fungicide to treat them. You should also pluck out any damaged larkspur and throw it away.
You shouldn’t have a major problem with insects, although aphids are sometimes a nuisance. Simply use your favorite organic insecticide if you notice a pest problem.
Three more facts about larkspur: 1) Some types were used in Transylvania to prevent witches from visiting stables; it is thought the blue coloring is what made the witches turn away. 2) In certain areas, larkspur will reseed itself. 3) In tropical areas, larkspur does not grow well at all.