Delphiniums are tall, majestic flowering plants known for their vibrant colors and towering spires of blooms. These striking perennials create a dramatic vertical element in garden beds. Gardeners are drawn to their intense blues, purples, pinks, and whites, which add a classic cottage garden charm.
Choosing and Planting Delphiniums
Site Selection
Delphiniums thrive best in full sun, requiring at least six hours of direct sunlight daily for robust blooms. While they tolerate partial shade, insufficient sun leads to leggy growth and fewer flowers.
Well-draining, fertile soil is also important. Heavy clay soils cause root rot due to excess moisture. Amend soil with organic matter like compost or aged manure to improve drainage and fertility. Aim for a slightly acidic to neutral soil pH (6.0-7.0) for optimal nutrient uptake.
Planting
Plant delphiniums in spring after the last frost or in early fall. This allows plants to establish roots before extreme temperatures.
Dig a hole twice as wide and deep as the root ball. Place the plant so its crown sits at soil level. Space plants 18 to 24 inches apart for proper air circulation and mature growth. This spacing helps prevent fungal diseases by reducing humidity around foliage.
Essential Delphinium Care
Watering
Proper watering supports vigorous growth and abundant flowering. Delphiniums prefer consistently moist soil but are intolerant of waterlogging, which causes root issues.
During dry periods, provide about one inch of water per week. Water deeply and less frequently to encourage deeper root growth, making plants more resilient to dry spells. Adjust watering frequency based on soil type and local climate.
Fertilizing
Regular fertilization provides nutrients for delphiniums to maintain size and produce blooms. In early spring, apply a balanced granular fertilizer (e.g., 5-10-5 or 10-10-10) as new growth emerges. This supports plant vigor and prepares them for flowering.
A second application after the first bloom flush encourages a smaller, later round of flowers. Always apply fertilizers according to package directions, sprinkling around the base and watering thoroughly. Avoid direct contact with stems or leaves to prevent burning.
Staking for Support
Staking prevents tall delphinium varieties from bending or breaking, as heavy flower spires can be damaged by rain and wind. Install stakes when plants are 12 to 18 inches tall, allowing them to grow around the support.
Use individual bamboo stakes, metal grow-through grids, or sturdy garden hoops. For individual stakes, gently tie the main stem to the stake at several points with soft ties. Early support ensures stems remain upright and blooms are showcased.
Maintaining Delphinium Health
Pruning and Deadheading
Pruning and deadheading maintain delphinium health and encourage repeat blooming. Deadheading removes spent flower stalks, redirecting energy from seed production to new flowers. Cut faded spikes back to a strong leaf node or side shoot to stimulate a second bloom flush.
After the second bloom cycle, or when flowering finishes, cut the entire plant back to 6 to 8 inches above ground. This tidies the plant for dormancy and removes diseased or damaged foliage, contributing to vigor.
Managing Pests and Diseases
Delphiniums are susceptible to pests and diseases, requiring proactive management. Slugs and snails are common, especially on young shoots, and can be controlled with organic baits or hand-picking. Aphids on new growth can be managed with insecticidal soap sprays.
Fungal diseases like powdery mildew and black spot affect foliage, particularly in humid conditions or areas with poor air circulation. Adequate spacing and watering at the base prevent these issues. If fungal diseases appear, apply a suitable fungicide per instructions. All parts of the delphinium plant are toxic if ingested by humans or pets; exercise caution when handling.
Winter Care
Proper winter care ensures delphiniums survive cold months and return vigorously in spring. After cutting back foliage following the final bloom or first hard frost, prepare plants for dormancy. This late-season pruning prevents diseases from overwintering on decaying plant material.
Apply a generous 4 to 6-inch layer of mulch (straw, shredded leaves, or wood chips) around the plant base. This insulates the crown and roots from extreme temperature fluctuations and freezing. Gradually remove mulch in early spring as new growth emerges to prevent rot and allow soil to warm.
Popular Delphinium Types
Many delphinium types offer a range of sizes and bloom forms. The Pacific Giant series is known for towering spires, 5 to 7 feet tall, with dense flower heads in classic blues, purples, and whites. These varieties are common in traditional cottage gardens.
The New Millennium series offers improved vigor, stronger stems, and a wider array of vibrant colors. These robust hybrids often produce multiple flower spikes.
Belladonna delphiniums feature a more open, branched form with smaller, less dense florets, typically growing 3 to 4 feet tall. These types provide a lighter, airy feel to a planting.