The delphinium, a spiky bloomer, is a hallmark of romantic cottage gardens.
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Key Takeaways
They’re strikingand unmistakable.
In a garden design, they can add visual interest with height, shape, and color.
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If you have many low-to-the-groundplantings 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.
They like full sun with afternoon shade in hot climates and need shelter from strong winds.
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Read on to learn how to make delphiniums feel at home in your garden.
Delphinium seeds and seedlings are toxic to people, dogs, cats, and horses.
Standing water causes crown and root rot, so a well-drained site is a must.
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To prevent disease, plant in an area that allows good air circulation and where theyre not overcrowded.
These plants need rich soil that’s very porous, and they do best with regular watering and feeding.
Because they grow to considerable heights, these flowers also require staking to ensure stability in the garden.
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Stake them with sturdy supports and attach at 12- to 18-inch intervals.
Prepare the planting site withorganic matter or compostto 1 foot deep.
The top of the rootball should be level with the soil.
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The roots need cool, moist shade.
Soil
Well-drained,humus-rich soilis a must, preferably slightly acidic to neutral.
For finicky delphiniums, soil quality plays a major role in success or failure.
Water
Water deeply during rainless periods, but dont 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.
The ideal range for delphinium is between 60F to 75F during the day and 45F to 55F at night.
Fertilizer
Use a balanced, slow-release fertilizer to promote healthy growth and flowering.
Applyfertilizer in early springand midsummer.
Carolina larkspur (D. carolinianum)
This plant is native to the Southeast and Midwest.
It has a narrow form and bursts into a heavy showing of blue orwhite bloomsin spring.
Afterward, during the summer months, it goes dormant.
Prairie larkspur (previouslyD.
virescens), also called white larkspur, is a sub-species that’s native from Texas to Canada.
It produces bright blue flowers and reaches heights of 3 to 6 feet tall.
It’s both a drought- and shade-tolerant planting.
Thin established plants to five to seven of the best shoots.
In autumn,prune the entire plantto the ground after it wilts to encourage new growth in spring.
They can also begrown from seed.
Here’s how to propagate by division and cuttings.
Germination can be poor after a year, so use fresh seeds.
Smaller rather than larger tray size is also recommended.
Give the seeds bright light and keep the soil moist.
Transplant after plants have two true sets of leaves.
Seeds collected from hybrids growing in the garden may not produce offspring that bloom true to color.
Avoid clay or terracotta pots that may dry out quickly.
Potted delphinium will require more water than those planted in the ground.
Fill the pot with loose potting mix or a combination of compost and perlite.
Backfill with soil and water thoroughly.
Place the pot in an area that shelters the plant from wind.
Tall varieties may need to be staked.
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.
Useorganic mulchsuch as bark, straw, pine needles, dry grass, or chopped leaves.
It also conserves soil moisture.
High humidity, soggy soil, and watering over the leaves can contribute to these diseases.
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.
Treat with insecticides as needed.
After blooms fade, cut stalks nearly to the ground, leaving foliage at the bottom.
Fertilize again and you may get a second bloom."
Common Problems With Delphinium
Proper care and growing conditions can help ensure healthy delphiniums with few problems.
Pests, poor soil, inadequate watering, and overcrowding can cause issues.
Leaves Turning Yellow
Yellow leaves can be a sign of overwatering or poor nutrition.
It can also indicate crown rot, when the base of the plant has been affected by fungus.
Adequate water, watering at the base of the plant, and using well-drained soil can prevent this problem.
Fertilizer can boost nutrition.
Ensure the plant has adequate water,good drainage, and shows no signs of pests or disease.
Tall varieties may need staking to support their heavier weight.
Propagating delphiniums provides a continuous supply of the plants in the garden.
Delphinium seeds can be started indoors and transplanted outdoors once the seeds are germinated.
They do not make ideal houseplants because their growing conditions are hard to reproduce indoors.
Choose companion plants with similar growing requirements and complementary colors.
Salvia, peonies, geranium, catmint, columbine, roses, and foxglove are all good companion plants.
American Society for the Prevention of Cruelty to Animals.Larkspur.
