Garden Scheme

Plant library  ·  Perennial Flowers

Delphinium

Delphinium elatum

Delphinium brings tall blue flower spires to the back of a perennial border in early to midsummer. At about 5 feet tall and 2 feet wide, it creates a strong vertical layer behind lower flowering plants rather than a compact filler. Its perennial presence suits USDA Zones 3 through 7, where the clump can hold a consistent place in a long-term bed plan.

  • Pollinator friendly
  • Deer resistant
Sunlight Full Sun
Water Regular
USDA zones 3–7
Spacing 2 ft
Mature size 5 ft tall, 2 ft wide
Bloom Early summer - mid summer

Placement and use

Give delphinium a full-sun position in a sheltered part of the garden, away from wind funnels between buildings or along exposed path edges. Place it toward the rear or center of an island bed, where its height will not block shorter plants or sightlines. Install stakes or a discreet support ring at planting time, leaving a clear approach from a path or bed edge for tying stems as they rise.[1][2]

Spacing and mature footprint

Set plants 2 feet apart, center to center. That matches the expected 2-foot mature width, creating a continuous vertical rhythm without asking neighboring clumps to overlap heavily. Keep the planting line far enough inside the bed that stakes, stems, and surrounding foliage do not lean into a walk. Avoid packing lower perennials tightly against the crown; open space around each clump supports the needed air circulation.

Three plants set 2 ft apart, center to center; shaded circles show the 2 ft mature spread.

Sun, water, and soil

Reserve a sunny bed with rich soil and plan for regular watering through active growth. The soil should drain freely after rain or irrigation rather than holding water around the crown. A border that can be watered evenly is more useful than a dry, difficult-to-reach back corner, especially once the tall stems begin to develop.[1][2]

Seasonal notes

The main display arrives from early summer into midsummer, when the flower spires occupy their greatest height and need their support most. After flowering, remove spent spikes to keep the border orderly; cutting them back promptly can encourage a later flush. When the top growth dies back in fall, the bed opens again for nearby plants to carry the later-season view.[2]

Planning caveats

This is not a plant to squeeze into a narrow strip beside a busy path. Its tall stems need staking, shelter, and reach-in access, while the clump needs breathing room from neighboring foliage. Use it where a 2-foot-wide footprint and occasional maintenance will not interrupt circulation or obscure smaller plants in front.

Growing facts

Botanical name
Delphinium elatum
Type
Perennial
Category
Perennial Flowers
Lifecycle
perennial
USDA hardiness zones
3–7
Sunlight
Full Sun
Water
Regular
Plant spacing
2 ft
Mature size
5 ft tall, 2 ft wide
Bloom season
Early summer - mid summer
Pollinator friendly
Yes
Deer resistant
Yes
Native to North America
No

References

  1. How to grow perennial delphiniums — Royal Horticultural Society
  2. Delphinium elatum — Royal Horticultural Society

Editorial content updated 2026-07-20.