Delphinium plants, sometimes called “Delphi plants,” are popular garden perennials known for their striking vertical flower spikes. These stately blooms come in vibrant shades of blue, purple, pink, and white, often featuring a contrasting “bee” or eye. Delphiniums add height and charm to garden borders and cottage-style landscapes, making them a popular choice for their elegant appearance and diverse color palette.
Planting Your Delphiniums
Plant delphiniums in spring or early autumn when the soil is warm and moist, aiding root establishment. They thrive in full sun, ideally six to eight hours daily, though afternoon shade helps prevent heat stress in warmer climates.
Choose a site protected from strong winds, as their tall, hollow flower stalks are prone to damage. Delphiniums prefer rich, well-draining soil that is neutral to slightly alkaline (pH 6.0-7.5). Before planting, incorporate two to four inches of compost or aged manure to enhance fertility and drainage.
Dig a hole twice as wide as the root ball and just as deep, ensuring the plant’s crown remains level with the soil surface. Space plants two to three feet apart, depending on variety, for adequate air circulation. Backfill with amended soil, gently firming it, and water thoroughly to settle the roots.
Caring for Established Delphiniums
Ongoing care for established delphiniums involves consistent watering, appropriate fertilization, structural support, and timely deadheading. Delphiniums require regular watering, particularly during hot and dry periods, to keep the soil consistently moist but not waterlogged. Overwatering or poorly draining soil can lead to crown rot.
Delphiniums are heavy feeders, benefiting from a balanced liquid fertilizer applied every two to three weeks starting in early spring. Alternatively, a slow-release granular fertilizer can be applied in spring when new growth emerges. Mulching around the base of the plants with a two to three-inch layer of organic material, such as shredded leaves or compost, helps retain soil moisture and keeps the roots cool.
Staking is often necessary for taller delphinium varieties to support their heavy flower spikes and hollow stems, preventing them from falling over in wind or rain. Stakes should be inserted early in the growing season, when plants are around 12 inches tall, using materials like bamboo canes or plant support rings. Removing spent flower spikes, known as deadheading, encourages a second flush of blooms, extending the flowering period. For winter care, cut plants down to about 6 to 8 inches after the first hard frost, and apply mulch to protect roots, especially in colder climates.
Troubleshooting Delphinium Issues
Delphiniums can encounter common garden problems, including pests, diseases, and environmental stressors. Slugs and snails feed on leaves and stems, leaving ragged holes; manage them with handpicking, beer traps, or copper tape. Aphids and spider mites cause distorted or discolored foliage and can be controlled with insecticidal soaps or neem oil.
Fungal diseases include powdery mildew, a white coating on leaves often due to high humidity and poor air circulation. Prevent it by ensuring adequate spacing and avoiding overhead watering. Crown rot, characterized by wilting and decay at the plant’s base, results from overly wet soil conditions.
Wilting might indicate insufficient watering during hot, dry spells or root issues from waterlogging. Delphiniums prefer cooler temperatures and may struggle in prolonged hot, dry summers. Addressing these issues promptly helps maintain plant vigor and bloom quality.
Delphinium Safety and Toxicity
Delphinium plants are toxic to humans, cats, dogs, and horses if ingested. All parts of the plant contain toxic compounds, with the highest concentrations found in new growth and seeds. Ingestion can lead to symptoms including gastrointestinal upset like nausea, vomiting, and diarrhea.
More severe cases of poisoning can result in neurological effects such as muscle tremors, weakness, and even paralysis, potentially leading to respiratory or cardiac failure. It is advisable to wear gloves when handling delphiniums, as contact with the foliage can cause skin irritation in some individuals. Keep delphiniums out of reach of children and pets. If ingestion is suspected, immediate medical or veterinary attention is important.