Delphinium (Larkspur): Plant Care and Growing Guide

What is the difference between Delphinium and Larkspur?

Delphinium and larkspur are often confused with each other because of their common names and similar appearance, but they are two distinct plants. Here are some differences between the two:

• Scientific Name: Delphinium belongs to the genus Delphinium, while larkspur belongs to the genus Consolida.
• Common Name: Delphinium is commonly known by several names, including larkspur, candle larkspur, rocket larkspur, and bee larkspur. Consolida is also commonly known by the names larkspur, rocket larkspur, field larkspur, giant larkspur, and candle larkspur. Most of the confusion comes from the fact that these 2 species share the same common name, Larkspur.
• Plant Type: Delphinium can be annuals, biennials, or perennials, while Larkspur is annual.
• Flower Spikes: Delphiniums have a more elongated and dense flower spike with individual blooms tightly packed together. Larkspurs have a looser, less dense flower spike.
• Leaf Shape: Delphiniums have deeply lobed, palmate leaves, while larkspurs have more finely divided leaves.
• Height: Delphiniums tend to be taller, with some varieties reaching up to six feet tall (180 cm). Larkspurs typically range from two to four feet tall (60-120 cm).
• Blooming Season: Delphiniums bloom in early to mid-summer, while larkspurs bloom in late spring to early summer.
• Toxicity: Delphiniums are highly toxic if ingested, while larkspurs are less toxic.

What is Special about Delphinium?

• Vibrant color: They add vibrant colors to your garden with their striking, showy blooms.
• Stunning addition: They are a great addition to cottage gardens, cutting gardens, and border plantings. Tall varieties make them a standout feature in your garden.
• Pollinators-friendly: They attract pollinators like butterflies, hummingbirds, and bees to your garden.
• Long blooming season: They have a long blooming period, providing beautiful flowers for several weeks in the summer.
• Undemanding: They are easy to grow and do not require too much maintenance.
• Deer and rabbit resistant: Delphiniums are considered deer-resistant plants due to their bitter taste and toxic properties.

Where to Plant Delphinium

• Sunlight: Delphinium requires full sun to part shade. It needs a minimum of six hours of sun a day. In hot climates, it benefits from afternoon shade.
• Soil: Delphinium prefers well-draining soil that is rich in organic matter.
• Water: Delphiniums need consistent moisture, especially during the growing season. However, they don’t like to be waterlogged, so make sure the soil drains well.
• Wind: Delphiniums benefit from shelter from strong winds, as their tall spikes can be easily damaged.
• Temperature: Delphiniums 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 (-40°C). They can also grow in zones 8 to 9 but will likely require some afternoon shade to protect them from the heat. The ideal temperature range for delphiniums is between 60°F to 75°F (15°C to 24°C) during the day and 45°F to 55°F (7°C to 13°C) at night.
• Humidity: 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.
• Water: Delphiniums need consistent moisture, especially during the growing season. However, they don’t like to be waterlogged, so make sure the soil drains well.
• Placement: Delphiniums are commonly grown in borders and are a popular choice for cottage gardens due to their tall spires of colorful flowers that add vertical interest and charm to the garden. Plant them in a mixed border with other cottage garden favorites such as roses, peonies, and foxgloves. Use delphiniums as a backdrop to lower-growing plants or as a focal point in a mixed border. Consider planting delphiniums in groups of three or more to create a more impactful display.

When to Plant Delphinium

The timing of planting delphinium depends on the climate and the type of delphinium being planted. In general, delphinium seeds should be sown in early spring as soon as the soil can be worked. In areas with mild climates, delphiniums can also be planted in the fall for spring bloom.

How to Plant Delphinium

• Choose a sheltered location: Delphiniums prefer a spot with full sun to partial shade and rich, well-drained soil with a pH of 6.5 to 7.5.
• Prepare the soil: Loosen the soil to a depth of 12 to 15 inches (30-37 cm) and amend it with organic matter, such as compost or aged manure. Delphinium is a heavy feeder, so the more compost you add to your flower bed, the more spectacular your Delphiniums are likely to be.
• Dig the hole: Dig a hole that is twice as wide and as deep as the delphinium plant’s root ball.
• Plant the delphinium: Place the plant in the hole, ensuring that the crown is level with the soil surface. Backfill the hole with soil, gently tamping it down around the plant.
• Space your plants: Plant delphiniums 1 to 3 feet apart, depending on the variety and the size of the mature plant. When planting delphiniums, it is important to space them properly to allow for adequate air circulation and to prevent overcrowding. If planting in a container, choose a pot that is at least 12 inches in diameter (30 cm) and plant one delphinium per pot.
• Water the plant: Water the plant well after planting to settle the soil around the roots.
• Mulch the plant: Apply a layer of organic mulch, such as shredded leaves or bark, around the plant to help retain soil moisture and suppress weeds.

Growing Delphinium from Seed

Delphiniums may be grown from seed, but this can be quite challenging. Seed should be started indoors early in the year, and those plants will flower the first year. If seeds are sown directly in the ground, those plants will not flower until the following year.

• Sow the seeds indoors about 8 to 10 weeks before the last frost date in your area. Fill a seed tray with soil and sprinkle the seeds on top. Cover lightly with soil and mist with water.
• Place the tray in a warm and bright location, keeping the soil moist but not too wet. The seeds should germinate in about 10 to 14 days.
• Once the seedlings have developed two sets of true leaves, they can be transplanted into individual pots or containers.
• When the danger of frost has passed and the seedlings have grown to a height of 3 to 4 inches (7-10 cm), they can be transplanted into the garden. Dig a hole that is slightly larger than the root ball and place the seedling in it. Fill in the hole with soil and gently press down to remove any air pockets.

How to Care for Delphinium

Here are some tips for caring for delphinium:

• Watering: Delphiniums need regular watering to thrive, especially during hot and dry weather. Water deeply and regularly to keep the soil moist but not waterlogged.
• Fertilizing: Use a balanced, slow-release fertilizer to promote healthy growth and flowering. Apply fertilizer in early spring and midsummer.
• Mulching: Mulch around the base of delphiniums with organic matter, such as shredded leaves or compost, to help retain soil moisture and suppress weed growth.
• Support: Delphiniums can grow quite tall and may require staking or support to prevent them from falling over in windy or rainy conditions.
• Deadheading: Deadheading, or removing spent blooms, encourages the plant to produce more flowers and can prolong the blooming period.
• Pruning: Cut back the plant to its base after it has finished flowering to encourage new growth and prevent disease.

How to Propagate

Delphinium can be propagated by division, cuttings, and seed. Be aware that all parts of delphiniums are poisonous, and contact with foliage may irritate your skin, so wear gloves when handling plants and seeds.

• Division: The best time to divide delphiniums is in the spring. Dig up the plant and gently separate the clumps into smaller sections with a sharp, clean knife. Replant the sections at the same depth they were previously growing.
• Cuttings: Delphinium cuttings should be taken in the spring. Cut a 3- to 4-inch stem (7-10 cm) from the parent plant and remove the lower leaves. Dip the cut end in rooting hormone and plant in a pot filled with moist potting soil. Keep the soil moist and place the pot in a warm, bright location. Roots should begin to develop in 3-4 weeks.
• Seed: Delphinium seeds can be sown directly in the garden in the spring or started indoors in the late winter or early spring. Sow the seeds in a prepared bed, covering them lightly with soil, and keep the soil moist. Seedlings should emerge in 14-21 days. Thin the seedlings to 12-18 inches apart (30-45 cm).

Pests and Diseases

Delphiniums are susceptible to several pests and diseases. Here are some of the most common ones:

Aphids: These small insects can suck the sap from the leaves and stems of delphiniums, causing stunted growth and distortion. They can be controlled by spraying the plant with a strong jet of water or by applying insecticidal soap.

Crown rot: This fungal disease causes the base of the plant to rot, which can lead to wilting and death. It is often caused by overwatering or poorly-draining soil.

Gray mold: It usually occurs during wet and humid weather conditions and can cause the leaves, stems, and flowers of the plant to turn brown and become mushy.

Leafminers: Delphinium leafminers are tiny larvae that can cause significant damage to delphinium leaves. These pests tunnel inside the leaves, leaving a trail of damage that can result in the death of the plant. The leafminers are typically light green and can be difficult to spot, but the damage they cause is visible as white or brown patches on the leaves.

Powdery mildew: This fungal disease appears as a white powdery coating on the leaves, stems, and flowers of delphiniums. It can be prevented by ensuring good air circulation around the plant and avoiding overhead watering.

Root rot: This can occur if the soil is too moist, causing the roots to rot and the plant to wilt.

Slugs and snails: These pests can chew holes in the leaves of delphiniums, especially in damp conditions. They can be controlled by handpicking or by applying slug and snail bait.

Spider mites: These tiny pests can cause yellowing and browning of the leaves of delphiniums. They can be controlled by spraying the plant with a strong jet of water or by applying insecticidal soap.

Regular monitoring and prompt action can help prevent and control these pests and diseases in delphiniums.

Companion Plants for Delphinium

Delphiniums look great when combined with other perennial plants with similar growing requirements and complementary colors. Here are some examples of companion plants that go well with delphiniums:

• Salvia
• Nepeta (catmint)
• Geranium
• Alchemilla mollis (lady’s mantle)
• Paeonia (peonies)
• Veronica
• Aquilegia (columbine)
• Digitalis (foxglove)
• Roses

These plants will not only enhance the beauty of your garden but also help to create a healthy ecosystem by attracting pollinators and other beneficial insects.

Click here to compare all Delphinium varieties

Frequently Asked Questions

Why is delphinium poisonous?

Delphinium contains several toxic compounds, including alkaloids such as delphinine, ajacine, and others. Ingesting any part of the plant, particularly the seeds and young leaves, can lead to symptoms such as skin irritation, upset stomach, difficulty breathing, and in severe cases, paralysis, and death.

What does a delphinium symbolize?

Delphiniums are often associated with the symbolism of purity, innocence, and grace. In the language of flowers, delphiniums represent a range of meanings, including joy, fun, and goodwill toward others. The color of the delphinium can also affect its symbolism, with blue delphiniums representing dignity and royalty, while pink delphiniums symbolize youth and love. Overall, delphiniums are considered to be a classic and elegant flower, often used in formal floral arrangements and garden designs.

Can you grow delphiniums in pots?

Yes, delphiniums can be grown in pots. It’s important to choose a large enough container that can accommodate the plant’s deep root system. The pot should also have drainage holes to prevent waterlogging. Delphiniums grown in pots may require more frequent watering and fertilization than those grown in the ground. Additionally, they may be more susceptible to temperature fluctuations, so it’s important to monitor their environment and protect them from extreme heat or cold.