How to Grow Larkspur from Seed

Larkspur is a cool-season hardy annual, which means it does its best work in the chilly shoulders of the year and fades once summer heat arrives. Sow the seeds directly in the garden rather than starting them indoors, because larkspur grows a taproot and resents being moved.

In mild-winter regions like the Southeast, Texas, and the Pacific Coast (roughly USDA zones 7 and warmer), scatter seed in fall so it germinates over winter and blooms early. In colder areas such as the Upper Midwest and New England, sow as soon as the soil can be worked in late winter or very early spring, a good 4 to 6 weeks before your last frost date, since the seeds actually prefer cold ground to sprout.

Pick a spot in full sun with loose, well-drained soil. Larkspur is not fussy about fertility, but it will rot in ground that stays soggy.

Rake the bed smooth, then sow the seeds about 1/8 inch deep and cover them fully, since larkspur needs darkness to sprout. Water gently to settle the seed and keep the surface evenly moist until seedlings appear. Once the little plants are a couple of inches tall, thin them to stand 8 to 12 inches apart so each one has room for a strong stem.

Germination usually takes 14 to 21 days and runs faster in cool soil, around 50 to 55 degrees F. If you are sowing in spring in a warm area, tuck the seed packet in the refrigerator for a week or two first. The chill mimics winter and wakes the seeds up for better, more even sprouting.

Water larkspur about 1 inch a week when rain is short, aiming at the base of the plant to keep the foliage dry and discourage mildew. The plants are light feeders, so a single dose of balanced fertilizer or a scattering of compost as they start to grow is plenty. Too much nitrogen gives you leaves instead of flowers.

Taller varieties can get top-heavy, especially after rain or in a windy spot, so either grow them in a sheltered block where they lean on each other or add a few stakes or a grow-through grid while the plants are still short. Larkspur grows fast and flowers hard for several weeks in late spring and early summer, then naturally winds down as the heat climbs.

Larkspur mixes happily with other cool-season, direct-sown cottage flowers that share its timing and taste for a sunny bed.

• Bachelor's buttons (cornflower): Sows and blooms on the same cool-season schedule and echoes the blue tones.
• Snapdragons: Add a different flower shape at a lower height while larkspur rises behind them.
• Sweet peas: Climb nearby for a fragrant, old-fashioned pairing that enjoys the same early start.
• Nigella (love-in-a-mist): Self-sows alongside larkspur and fills the gaps with airy foliage and seed pods.
• Calendula: Brings warm orange and yellow that plays off larkspur's cool spires and feeds pollinators.

Keep larkspur out of vegetable beds and any area where children, pets, or livestock graze, since every part of the plant is toxic if eaten.

Larkspur blooms from the bottom of the spike upward over a couple of weeks, which makes it a generous cut flower. Snip stems in the early morning when about a third to half of the florets on the spike have opened, and they will keep opening in the vase.

Deadhead spent spikes to push the plant toward side shoots and a longer show. If you want volunteers next year, leave a few of the last spikes to form seed and drop it. The flowers also dry well: hang small bunches upside down in a dark, airy spot and they hold their color for months.

Larkspur earns its keep as a cut flower, both fresh in the vase and dried for wreaths and arrangements that last into winter. In the garden its tall spires add vertical lines to borders and cottage plantings, and it looks especially good woven among rounder, bushier flowers. Bees and butterflies work the blooms steadily, so a patch doubles as a pollinator stop in late spring.

• Slow or patchy germination: Larkspur needs cool soil and darkness. Sow early while the ground is still cold, cover the seed completely, and chill the seed in the fridge for one to two weeks before a spring sowing.
• Powdery mildew: A white, dusty film shows up in crowded, humid plantings. Give plants room, water at the base rather than overhead, and keep air moving between them.
• Floppy, bent stems: Tall spikes lodge in wind and heavy rain. Plant in a sheltered block or set stakes or a grow-through grid early, before the plants need them.
• Aphids on buds and stems: Blast them off with a sharp spray of water and let ladybugs and lacewings mop up the rest.