Quck answer
Delphiniums are beautiful flowering plants that can add color and height to your garden. To grow delphiniums successfully, follow these steps:
1. Choose a sunny location with well-draining soil.
2. Prepare the soil by adding compost or organic matter.
3. Plant delphinium seeds or young plants in early spring or fall.
4. Water regularly, keeping the soil evenly moist but not waterlogged.
5. Stake tall varieties to support their growth.
6. Mulch around the plants to retain moisture and suppress weeds.
7. Fertilize with a balanced fertilizer once a month during the growing season.
8. Deadhead spent flowers to encourage continuous blooming.
9. Protect the plants from strong winds and heavy rain.
10. Divide mature plants every 2-3 years to maintain their vigor.
By following these steps, you can enjoy the beauty of delphiniums in your garden and create a stunning display of vibrant colors.
When describing plants, the word “showy” is often used, but this is especially true when it comes to delphiniums (​Delphinium spp.​). The plant’s tall, elegant spikes are covered with numerous small flowers. Although delphiniums are typically associated with blue flowers, cultivars with pink, crimson, white, and purple blooms are also available.
While these plants are stunning to look at, they can be temperamental and require a lot of care. Delphiniums do not thrive in hot, dry summers and prefer cooler temperatures and moist soil. It is essential to maintain a consistent watering schedule to keep the soil moist. Additionally, they often require protection from strong wind and heavy rain. Taller varieties must be staked to prevent them from falling over.
Despite their high maintenance, delphiniums, if cared for properly, offer two blooming seasons: one in June and July at the beginning of summer and another in late summer through fall. They are also attractive to hummingbirds and butterflies.
Simple Steps for Growing Delphiniums
- When planting directly into the garden, mix organic matter like compost with the top 8 to 12 inches of soil.
- Plant the seeds and cover them with 1/8 inch of soil. Keep the soil moist.
- When the plants have three sets of leaves, thin them to 12 to 18 inches apart.
Best Uses for Delphiniums
Delphiniums are often found in cottage gardens, particularly those that receive full sun for most of the day but have some afternoon shade.
- Due to their height, they work best at the back of a perennial border or in the center of a circular garden.
- Plant them in mass if there is enough space, but even small groups of three or five can become a garden focal point.
- Dwarf varieties are suitable for potted plants that can be placed in outdoor living areas or around the entrance to a home. They are a favorite of cutting gardens.
Tip
After the first set of flowers fades in June or July, cut the flower stalks to the ground. This often leads to a second round of blooms in early to mid-fall.
How to Grow Delphiniums
|
Common Name |
Delphinium |
|
Botanical Name |
​Delphinium elatum​ |
|
When to Plant |
For indoor seeding, sow eight to ten weeks before the last spring frost date. For outdoor planting, sow directly into the garden in late spring. In warm regions like zone 7, seedlings can be planted in the fall. |
|
USDA Zones |
3-7 |
|
Sun Exposure |
Full sun to partial shade, particularly in very hot climates |
|
Soil Type |
Well-draining and slightly alkaline |
|
When It’s in Trouble |
The plant displays stunted growth with yellow foliage, often due to a lack of fertilizer. |
|
When It’s Thriving |
The spikes are upright and sturdy, with vibrant flowers. |
How to Start Delphiniums from Seed
To start delphiniums from seed, begin indoors eight to ten weeks before the final spring frost date. Place the seeds in the refrigerator for about a week before sowing to give them a cold start boost. Then, cover the seeds with about 1/8 inch of starter soil in the trays of a seed-starter kit and keep the soil moist at around 70 degrees Fahrenheit. It takes about three to four weeks for the seedlings to emerge. Once they have developed two pairs of true leaves, move them from small cells to 4-inch pots and place them under a fluorescent grow light or a sunny windowsill. Keep them under the light for 16 hours per day and in the dark for the remaining eight. Before moving the young plants to the garden, harden them off by gradually introducing them to outside conditions over the course of about a week in a sheltered outdoor spot. To sow seeds directly into the garden, mix the top 8 to 12 inches of soil with organic matter and cover the seeds with 1/8 inch of soil. Keep the soil moist, and the seedlings should emerge in approximately three to four weeks. Thin the plants to 12 to 18 inches apart once they have three sets of leaves.
How to Start Delphiniums from a Seedling
Growing delphiniums from a seedling is less complicated. Prepare the soil by mixing the top 12 inches with organic matter, space the plants 12 to 18 inches apart, and dig a hole twice the diameter of the pot containing the young plant. Loosen the roots with your fingers and place the plant in the hole so that the top of the root ball is even with the surrounding area. Water the plant and cover the area around it with a few inches of mulch to keep the soil moist, but keep the mulch away from the stems to avoid encouraging pests and decay.
Which Zone is Best for Delphiniums?
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Jill Ferry/Moment/GettyImages
Delphiniums grow best in USDA zones 3 to 7, but it is essential to consider the microclimate, or local climate condition. Delphiniums do not thrive in hot conditions and may struggle during summers in warmer regions. For optimal growth, plant them where they can receive full morning sun but some afternoon shade. Additionally, planting delphiniums against fences or the side of a house can help protect them from strong winds as their stems are hollow.
What is the Best Time to Plant Delphiniums?
Delphiniums are mostly planted in the spring, but can also be planted in the fall in warm areas. If you live in a temperate climate, it is recommended to start planting seeds indoors around Labor Day for November planting. Delphiniums planted in the fall should bloom the following spring. If you are planting young plants, it is advised to work on a cloudy day or late in the afternoon to prevent transplant shock.
Although delphiniums usually produce flowers in the first year, they reach their full potential in the second year with a full complement of flowers and multiple stems.
What Soil, Sunlight, and Water Do Delphiniums Need?
Proper care is essential for delphiniums once they are planted in the ground. Here are some requirements for them to thrive:
Soil Requirements for Delphiniums
Delphiniums require nutrient-rich, well-draining soil and can tolerate neutral to slightly alkaline soil as measured on the pH scale. Testing the pH of your soil before planting can determine what nutrients your soil is lacking. Garden centers and DIY testing kits are available for testing the soil. Delphiniums are heavy feeders, so it is crucial to mix organic matter with the soil at planting time and side-dress the plants with compost or balanced liquid fertilizer every two to three weeks during the growing season.
Sunlight for Delphiniums
Plant delphiniums in areas that receive direct sun for six to eight hours per day. In hot areas, it is recommended to avoid too much heat and provide afternoon shade.
Water Requirements for Delphiniums
Delphiniums require deep watering at least once a week until young plants are established. During the season, the soil should be kept moist but not sopping wet, and the top 1 inch of soil should remain moist at all times. Watering early in the day helps avoid evaporation and promotes quick drying of leaves. Ground-level soakers or drip irrigation systems are efficient ways to water the plant at the base.
How to Propagate Delphiniums?
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wjarek/iStock/GettyImages
The best time for propagating delphiniums is in the spring when the plants in your garden start to grow. Take a 4-inch cutting from one of the side shoots.
To propagate delphiniums, cut below the soil line and remove all but a few top leaves from the cutting. Dip the bottom of the cutting in rooting hormone and plant it in a small pot with potting mix. Keep the soil moist and place the pot in a spot that isn’t exposed to direct sunlight. Once new growth appears after three or four weeks, the root system has started to develop. By late summer or early fall, you can plant the cutting in the garden. Delphiniums should be divided every three years. Use a soil knife or sharp shovel to separate the outer sections from the heart of the root system, and replant the divided sections to produce more plants.
To prepare delphiniums for winter, continue to water them until the ground freezes. After the first hard frost, cut the plant back to around six inches from the ground and remove debris from around it. Add 3-4 inches of natural mulch to retain moisture and protect the crown of the plant during the cold months. Avoid using large whole leaves for mulch, as they can damage the plant. If you want to use leaf mulch, cut up the leaves with a lawn mower first.
Slugs and snails can damage young delphinium plants, but you can discourage them by keeping the area free of weeds and debris. Some gardeners recommend burying a shallow saucer of beer so that the pests will crawl in and drown. Cyclamen mites can destroy plants by sucking the juices from leaves and stems, but keeping the plants well-watered can help prevent infestations. Leafhoppers spread disease and can be controlled with insecticidal soap or commercial insecticides. Powdery mildew is a fungal disease that can be treated with fungicide. Aster yellows is a virus that is spread by leafhoppers and has no cure, so infected plants should be removed and leafhoppers controlled.
Protecting Delphiniums from Fungal and Bacterial Pathogens
It is important to protect delphiniums from fungal and bacterial pathogens that can cause rotting of their stems, crowns, and roots. Symptoms of infection include yellowing leaves, blackened stems, and a foul-smelling ooze. If infected, it is best to destroy the plant to prevent the spread of the disease. Preventative measures can be taken by avoiding overhead irrigation, which creates conditions that foster these diseases.
FAQ
1. What are the ideal conditions for growing delphiniums?
Delphiniums thrive in cool climates and require full sun for at least six hours a day. They prefer well-drained soil with a pH level between 6.5 and 7.5. It’s important to provide them with sufficient air circulation to prevent diseases. Additionally, delphiniums benefit from regular watering, especially during dry spells, to keep the soil moist but not waterlogged.
2. How should I plant delphiniums?
To plant delphiniums, choose a location with plenty of sunlight and prepare the soil by removing any weeds and adding organic matter, such as compost, to improve drainage. Dig a hole that is twice the size of the root ball and place the delphinium plant in the hole, making sure the crown is level with or slightly above the soil surface. Backfill the hole with soil, firming it gently around the plant, and water thoroughly.
3. How do I care for delphiniums during the growing season?
During the growing season, it’s important to provide delphiniums with regular care. Keep the soil consistently moist, but avoid overwatering, as it can cause root rot. Apply a balanced fertilizer every four to six weeks to promote healthy growth. Additionally, stake tall varieties to prevent them from toppling over in strong winds. Deadhead spent flowers to encourage continuous blooming, and remove any yellow or diseased leaves promptly to prevent the spread of diseases.