HARDINESS: Freeze tolerant
PREFERRED SOIL pH: Neutral to slightly alkaline
PREFERRED SOIL TYPE: Fertile, well-drained
PREFERRED LIGHT: Sun
ATTRIBUTES: Pastels flower spires; for flower or herb gardens, fresh cut or dried flowers
SEASON OF INTEREST: Spring to summer, depending on climate
FAVORITES: 'Giant Imperial' for many colors, tan spires; 'Messenger' for early flowers
QUIRKS: Toxic plants and seeds; poor transplant survival
GOOD NEIGHBORS: Alliums, poppies, monkshood, peonies, yarrow
WHERE IT GROWS BEST: Moist, fertile, alkaline soil; cool weather
POTENTIAL PROBLEMS: Powdery mildew, crown rot, root rot
CRITTER RESISTANCE: Good
DIMENSIONS: 3-4 ft (1-1.2 m) toll, 1 ft (0.3 m) wide
Larkspur in the Landscape
Larkspur was once a mainstay of the garden, just as popular as roses, lilies, and hollyhocks. Apt to be found in every garden, the airy flowers of larkspurs were also apt to be seen in every garden bouquet. In recent years, delphiniums, their close relatives, have stolen larkspurs' place of honor in garden beds. Although it's true that perennial delphiniums have larger spires composed of fancier flowers, they can't beat larkspurs for care-free cultivation. There's also no comparison when it comes to nostalgic appeal. Something about the 3 ft (1 m) spires bristling with snow white, tissue pink, powder blue, or navy blue florets tugs at our hearts.
Comfortable in herb gardens as well as flower beds, larkspurs are especially eye-catching when planted where their blue flowers can echo the color of a nearby pond or patch of sky. But larkspurs look best in a small grouping of mixed colors. The Giant Imperial series, with a color range that includes carmine, deep blue, rose, powder blue, lilac, pink, salmon, and white, is the standard for cut-flower purposes. The 'Messenger' series blooms 2 weeks earlier.
Unlike the upright-growing, high-maintenance delphiniums, larkspurs are informal, open-limbed plants that are likely to self-sow and sprout in just the right place without effort on your part. But, given a choice, they'd like to have fertile, fluffy, well-drained soil with plenty of lime and regular, reliable moisture. To insure that the spires aren't buffeted by wind, stake them as they begin to shoot up.
Increasing the Bounty
If larkspurs have any failure, it is that the flowers don't linger long. Because hot weather is not to their liking, sow larkspurs in the garden in early spring when the ground thaws, or in autumn for flowering the following spring. In cold regions, sow in September; in Zones 7 to 9, you can safely sow until the end of November. The seeds can take up to 20 days to sprout, and germination from fall sowing is often erratic. The goal is to get larkspurs to sprout as early as possible. The seedlings tolerate extreme cold, but mature plants subjected to nighttime temperatures above 55°F (13°C) for any length of rime fail to flower well.
Larkspurs don't like to be transplanted. It's more effective to sow the seeds directly in the ground than attempt to transplant seedlings. Larkspur seeds require darkness to germinate, so sprinkle them over good garden soil and cover them with a thin layer of finely sifted soil. Sprinkle to moisten the seedbed, keeping it moist until they sprout.
Although pests aren't usually a problem, larkspurs sometimes succumb to fungal diseases, such as powdery mildew, crown rot, and root rot. Increasing air circulation by thinning plants is an effective preventative for mildew, while rotating, or sowing seeds in different locations every year, and incorporating compost into the soil to improve drainage will keep rot from occurring. The seeds and leaves of larkspurs are poisonous if eaten, so place the plants in an area away from children and pets.