Crop Rotation Group
Miscellaneous
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Soil
Fertile, well-drained soil enriched with compost, with a neutral to slightly alkaline pH.
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Position
Full sun with shelter from strong wind; partial shade where summers are hot.
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Frost tolerant
Yes, delphinium is a hardy perennial. Well-rooted plants are hardy to -30°F (-34°C). The plants prefer cool weather and cannot tolerate long periods with warm, humid nights.
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Feeding
Mulch over the plants’ root zones with rich compost just as the new growth emerges in spring. Drench plants with a balanced organic fertilizer in late spring when the plants are producing vigorous new growth, and again in late summer to stimulate a fall flush of flowers.
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Companions
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Spacing
Single Plants: 11" (30cm) each way (minimum)
Rows: 11" (30cm) with 11" (30cm) row gap (minimum)
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Sow and Plant
Bare-root or potted plants of improved varieties and native strains are widely available in spring, or you can start seeds indoors in late winter. The Belladonna types are the best delphiniums to grow from seed, which must be fresh. At room temperature, delphinium seeds will germinate in 10 to 15 days. Set out purchased plants or seedlings as early as possible, while the soil is still cool. Plants may bloom a little the first year after planting, with stronger flower production in subsequent seasons. Delphiniums do not tolerate dry conditions, so try to keep the roots lightly moist at all times. A surface mulch suppresses weeds while making the plants look more attractive.
Our Garden Planning Tool can produce a personalized calendar of when to sow, plant and harvest for your area.
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Notes
Tall delphiniums require staking to keep them upright, while more compact delphiniums need less exacting care. These beautiful flowers either love or hate certain sites, so try them in more than one location. All plant parts are poisonous. In addition to large-flowered perennial delphiniums, there are many species native to North America worth including in wildflower gardens, such as D. tricorne (dwarf larkspur) in the east and D. hesperium (Western larkspur), among others.
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Harvesting
Gather the first flower spikes as soon as half the blossoms have opened. Harvesting the first spikes encourages the development of more blooms. In climates with cool summer nights, many delphiniums will bloom a second time in the autumn when given good care.
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Troubleshooting
Slugs chew holes in leaves with smooth edges. Aphids and cyclamen mites weaken plants by feeding on leaf undersides and stems. Warm, rainy weather can lead to problems with blossom rot and crown mold.
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