How To Grow And Care For Delphinium Flowers

They're striking—and unmistakable. Delphiniums are towering columns of bright blooms that can reliably add a dose of drama to any landscape. They're often found in classic English cottage gardens, and their distinctive blooms are great additions to cutting gardens across the U.S. as well.

While these flowers have developed a reputation for being finicky plantings in the Southern states—they balk at the heat and humidity of our summers—they're just plain gorgeous, which is why we've figured out ways to keep planting them. Read on to learn how to make delphiniums feel at home in your garden.

Prepare the planting site with organic matter or compost to 1 foot deep. Plant delphiniums in a hole that is twice the diameter of the container and backfill with soil that has been well-mixed with the organic matter. The top of the rootball should be level with the soil.

Other than the dwarf varieties, delphiniums require staking. Their hollow stems will break when blown in the wind or when the flowers become weighed down from rainfall. Stake them with sturdy supports and attach at 12- to 18-inch intervals.

Plant Attributes

Delphinium Care

Delphiniums usually bloom during the spring and early summer months, and they produce tall columns of brightly colored flowers in shades of blue, pink, lavender, yellow, red, and white. The native species are reliably perennial, and some of the striking (though more difficult to tend) hybrid species can be treated as annuals if necessary.

Delphiniums should be planted in an area that receives 6 to 8 hours of sun per day, preferably morning sun. They need shelter from strong winds and rain downpours to avoid damage to the tall flower stalks. Standing water causes crown and root rot, so a well-drained site is a must. To prevent disease, plant in an area that allows good air circulation and where they’re not overcrowded.

In a garden design, they can add visual interest with height, shape, and color. If you have many low-to-the-ground plantings in your cutting garden, consider adding delphiniums for an infusion of vertical variety. While most delphinium species reach heights from 1 to 6 feet tall, some hybrids grow much higher.

Light

Delphinium plants require 6 to 8 hours of sun a day, and gentle morning and early afternoon sun is preferred. The roots need cool, moist shade.

Soil

Well-drained, humus rich soil is a must, preferably slightly alkaline. Although mulch helps preserve moisture in the soil, if it is applied too closely to the stems it can cause them to rot. For finicky delphiniums, soil quality plays a major role in success or failure.

Water

Water deeply during rainless periods, but don’t allow standing water. Delphiniums like it moist, but water that lingers causes crown and root rot. Water delphiniums at the base, keeping the foliage dry to help prevent disease.

Temperature And Humidity

These plants prefer cool to moderate temperatures and do well in USDA hardiness zones 3 to 7, where they can tolerate temperatures as low as -40°F. The ideal range for delphinium is between 60°F to 75°F during the day and 45°F to 55°F at night.

High humidity and excessively hot temperatures can cause the plants to wilt and weaken, so it's important to ensure they are planted in a location with good air circulation and well-draining soil.

Fertilizer

Use a balanced, slow-release fertilizer to promote healthy growth and flowering. Apply fertilizer in early spring and midsummer.

Types Of Delphiniums

Candle delphinium (Delphinium elatum)

Also known as candle larkspur, this delphinium species blooms in shades including blue, purple, pink, and white. This group is where you'll find many hybrid selections, including the Pacific strain hybrids, which have been known to grow to 8 feet tall. Selections include'Percival,' which is white with a black center; 'Summer Skies,' which blooms in light blue hues; and 'Blue Bird,' which has bright blue flowers.

Carolina larkspur (Delphinium carolinianum)

This plant is native to the Southeast and Midwest. It has a narrow form and bursts into a heavy showing of blue or white blooms in spring. Afterward, during the summer months, it goes dormant. Prairie larkspur (previously Delphinium virescens), also called white larkspur, is a sub-species that's native from Texas to Canada. It's heat-tolerant and produces tall stalks of delicate, widely spaced white flowers that bloom from spring into summer.

Chinese delphinium (Delphinium grandiflorum, D. chinense)

Also known as bouquet delphinium or Siberian larkspur, this heat-tolerant species produces large, deep blue flowers that grow in bushy masses of loose, asymmetrical formations. Selections include 'Dwarf Blue Mirror,' which grows to 1 foot tall, and 'Tom Thumb,' which grows to 8 inches tall.

Delphinium x belladonna

This delphinium group produces full, dense forms with light and delicate clusters of flowers. Selections include 'Belladonna' (light blue), 'Bellamosum' (dark blue), 'Casa Blanca' (white), and 'Cliveden Beauty' (deep turquoise).

Tall larkspur (Delphinium exaltatum)

Tall larkspur is native to the U.S. and grows north to Pennsylvania and south to Alabama. It produces bright blue flowers and reaches heights of 3 to 6 feet tall. It's both a drought- and shade-tolerant planting.

These plants need rich soil that's very porous, and they do best with regular watering and feeding in a spot where they can receive full sun. Because they grow to considerable heights, these flowers also require staking to ensure stability in the garden. To get them started, per The Southern Living Garden Book, "Delphiniums are easy to grow from seed. In the Middle, Lower, and Coastal South, sow fresh seed in flats or pots filled with potting soil in July or August, and set out transplants in October for bloom in late spring and early summer. In the Upper South, sow seed in March or April and set out transplants in June or July for first bloom by September (and more bloom the following spring)."

Pruning

To encourage best flowering, thin new plants to 2 to 3 good shoots when they are 3 inches high. Thin established plants to 5 to 7 of the best shoots. Cut the main stalk down after flowering to the level of its smaller side shoots, which will bloom secondarily with slightly smaller flowers. To encourage a second, but smaller, bloom in late summer or early autumn, cut the stalks to the ground just after flowering. Prune the entire plant to the ground after it wilts in autumn.

Growing Delphinium From Seed

September to March is the best time to propagate delphiniums from seed. Germination can be poor after a year, so use fresh seeds. Presoaking the seeds is recommended to improve the germination rate, along with ensuring temperatures of 65 at night and 75 during the day are available while germinating.

Cover seeds with only one-eighth inch of soil and keep evenly moist, but not wet as this can cause them to rot. Smaller rather than larger tray size is also recommended. Transplant after plants have two true sets of leaves.

It is common for delphiniums not to bloom the first year, so be patient and you should see them come to life in the second year. Seeds collected from hybrids growing in the garden may not produce offspring that bloom true to color.

Overwintering Delphinium

In preparation for wintering delphiniums, water the plants regularly as winter approaches and continue until the ground freezes so hard it can no longer absorb moisture. Do not use a sprinkler, use a hose and set it on trickle until the roots are thoroughly saturated. Shear the plants down to a height of 6 to 8 inches after the first killing frost in autumn. Remove leaves and other plant debris from around the plant to dissuade disease and pests, including slugs.

Layer on at least 2 to 3 inches of mulch in late autumn, when the ground is cold but not frozen. Use organic mulch such as bark, straw, pine needles, dry grass or chopped leaves. Mulch protects delphinium in a couple of ways: It prevents damage caused by freezing and thawing that can freeze the crown. It also conserves soil moisture.

How To Get Delphinium To Bloom

According to The Southern Living Garden Book, "If you live in the Upper South, you can set off a burst of delphinium blooms like those you see in English gardens. When new stalks appear in spring, remove all but the strongest two or three, tie to stakes, and apply a bloom-booster fertilizer. After blooms fade, cut stalks nearly to the ground, leaving foliage at the bottom. Fertilize again and you may get a second bloom."

Common Pests And Plant Diseases

Delphiniums are susceptible to a host of diseases including powdery mildew, Southern blight, bacterial and fungal spots, gray mold, crown and root rot, rust and others.

Planting your delphiniums in a well-ventilated area and keeping the foliage dry will go a long way in preventing disease. Care should be taken to protect young plants from snails and slugs, as they can cause considerable damage. Delphiniums are also commonly plagued by cyclamen mites, aphids and nematodes.

Delphinium Toxicity

All parts of the delphinium plant (especially the very young delphinium plants) can be harmful to humans and animals, so take care not to ingest them, and keep them away from children, pets, and livestock.