How to Grow and Care for Delphiniums

Delphiniums are stunning perennial flowers known for their tall spikes of colorful blooms. With their vibrant shades of blue, purple, pink, and white, they make an impressive addition to any garden. However, growing and caring for delphiniums requires attention to detail, as these plants have specific needs to thrive. Here’s a comprehensive guide on how to grow and care for delphiniums to ensure they flourish in your garden.

Choosing the Right Location

Delphiniums thrive in areas with full sun, which helps them produce the most robust and abundant blooms. Aim for a location that receives at least six hours of direct sunlight daily. The more sun they receive, the better the flower production. However, in extremely hot climates, delphiniums may benefit from some afternoon shade to protect them from the harshest midday sun.

The soil should be rich, well-drained, and slightly alkaline to neutral. Delphiniums prefer soil that is fertile, so adding compost or well-rotted manure to the soil before planting will help. Good drainage is crucial, as delphiniums are susceptible to root rot in soggy conditions.

Planting Delphiniums

Plant delphiniums in early spring or fall, depending on your climate zone. If you’re planting in the spring, wait until the threat of frost has passed. Delphiniums are often grown from seeds, transplants, or bare root plants.

1. From Seeds: Start delphinium seeds indoors in late winter, 8 to 10 weeks before the last expected frost. Sow seeds in small pots, just barely covering them with a thin layer of soil. Keep the seeds moist and in a bright location but out of direct sunlight until they germinate. Once the seedlings are large enough to handle, transplant them outdoors after the frost risk has passed.

2. From Transplants or Bare Root Plants: If starting with transplants or bare roots, dig a hole that’s slightly larger than the root ball of the plant. Space the plants about 18 to 24 inches apart to give them room to grow. Gently place the plant in the hole, ensuring the crown is level with the soil surface, and fill it with soil, pressing lightly around the base.

Watering and Feeding

Delphiniums need consistent moisture, especially during their growing season. Water them deeply and regularly, particularly during dry spells. However, avoid watering overhead, as wet foliage can lead to fungal issues. Instead, water at the base of the plant.

In addition to regular watering, delphiniums benefit from periodic feeding. Use a balanced, slow-release fertilizer or a liquid fertilizer every four to six weeks during the growing season. High-nitrogen fertilizers can encourage more leaf growth than blooms, so choose a fertilizer that’s higher in phosphorus to promote flower production.

Staking and Supporting Delphiniums

Delphiniums can grow quite tall, with some varieties reaching heights of 6 feet or more. Due to their height, they may need support to prevent the stems from bending or breaking, especially when they are covered with heavy blooms. Install stakes early in the growing season to avoid damaging the plant later. You can use individual stakes for each stem or set up a circular or grid-style cage around the plant.

When staking, ensure the stakes are firmly in the ground and gently tie the stems to them using soft twine or plant ties. This will allow the plant to grow without the risk of breaking under the weight of its blooms.

Pruning Delphiniums

Proper pruning is essential to maintaining a healthy delphinium plant. Remove any dead or damaged leaves or stems during the growing season to keep the plant looking tidy and to prevent disease. Once the flowers have finished blooming, you can cut back the flower spikes to about 6 inches from the base. This will encourage the plant to produce a second flush of blooms, particularly in varieties that are known for reblooming.

In fall, after the plant has gone dormant, you can cut the stems back to ground level to prevent any disease or pests from overwintering in the plant. However, don’t prune too early in the season, as delphiniums often have attractive seed heads that can provide visual interest in the garden during the winter months.

Winter Care

Delphiniums are hardy perennials, but in colder climates, they benefit from some winter protection. After cutting the stems back in the fall, apply a layer of mulch around the base of the plant to insulate the roots. A few inches of organic mulch, such as straw or shredded leaves, will help protect the plant from freezing and thawing cycles that can damage the roots.

In areas with very harsh winters, consider planting delphiniums in raised beds or containers that can be moved to a sheltered location during the coldest months. For plants growing directly in the ground, ensure the soil is well-drained to avoid waterlogging and root rot.

Pests and Diseases

Delphiniums are relatively disease-resistant, but they can be susceptible to a few common pests and diseases. Keeping the plants healthy and well-maintained is the best way to prevent issues. Here are some potential problems to watch out for:

1. Powdery Mildew: This fungal disease is often seen on delphinium leaves as a white, powdery coating. It’s most likely to occur during periods of high humidity and poor air circulation. To prevent powdery mildew, avoid overhead watering and space the plants adequately for good air circulation. If powdery mildew appears, treat the plant with a fungicide or a homemade remedy such as a mixture of water and baking soda.

2. Aphids: These small, soft-bodied insects can infest delphiniums and suck sap from the leaves, causing them to curl or yellow. You can remove aphids by spraying the plant with water or applying insecticidal soap.

3. Slugs and Snails: These pests are known to munch on delphinium foliage, especially in moist, shaded conditions. Using slug bait, diatomaceous earth, or creating barriers with crushed eggshells around the plants can help deter them.

4. Root Rot: To prevent root rot, ensure that delphiniums are planted in well-drained soil and avoid overwatering. Proper spacing also helps by improving air circulation around the roots.

Dividing Delphiniums

Over time, delphiniums may become overcrowded or produce fewer flowers. If this happens, it’s time to divide the plants. The best time to divide delphiniums is in early spring before new growth begins. Dig up the entire plant and carefully separate the root ball into smaller sections, ensuring each section has some roots and shoots. Replant the divided sections in the same type of soil and follow the same care instructions as for the original plant.

Conclusion

Delphiniums are a beautiful and rewarding plant to grow, adding height, color, and structure to your garden. While they require a bit of attention and care, particularly in terms of sun, soil, water, and support, their striking blooms are well worth the effort. By providing the right growing conditions, pruning regularly, and managing pests and diseases, you can enjoy healthy, vibrant delphinium plants year after year. Whether you’re a seasoned gardener or a beginner, delphiniums are sure to impress and enhance the beauty of your outdoor space.