Delphinium

Questions about delphinium

Does delphinium need sun or shade?

Delphinium grows in full sun (6 or more hours of direct sun a day).

It wants ordinary well-drained soil, rich in organic matter, and a good soak in dry spells.

What zones does delphinium grow in?

USDA zones 3 to 7. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).

Above zone 7 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does delphinium flower in my zone?

In zone 5 it flowers late June to mid July. As a summer flower it moves about half a week for every zone: earlier where it is warmer.

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should delphinium be planted?

24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is about its full width, so each plant keeps its own outline.

It grows 5 ft (150 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many delphinium plants do I need?

At 24 in apart, set out in staggered rows:

• 3 to fill 10 square feet (about 1 m²)
• 6 for a single row 10 ft (3 m) long
• 10 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.

In the bed above, the planner used three in one group.

Is delphinium poisonous to dogs and cats?

Yes: severe toxicity to people, dogs, cats and horses. All parts, especially the young growth and seeds, are highly poisonous if eaten.

Rated from NC State Extension and the ASPCA. Where references disagree, the more cautious rating is used.

Is there a pet-safe plant like delphinium?

These come closest to doing what delphinium does, and no toxicity is recorded for them:

• Culver's root: the same job in a bed and the same size; flowers early July to mid August, white or lavender, not blue.
• Carolina lupine: the same job in a bed; 12 in shorter, flowers late May to late June.
• Giant coneflower: the same job in a bed and the same flowering time; 12 in taller, yellow, not blue.

Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.

Do deer eat delphinium?

Mostly not. NC State lists it as resistant to deer and rabbits. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

What flowers after delphinium?

Delphinium is over by mid July. These start as it finishes and carry the same spot on, so it never goes flat:

• Russian sage: from mid July to mid September, 4 ft tall.
• Tiger lily: from late July to late August, 4 ft tall.
• Garden phlox: from mid July to early September, 3½ ft tall, to stand in front of it and cover its fading stems.

What does delphinium look like in winter?

Delphinium dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.

Is delphinium good for bees and butterflies?

Delphinium is visited by butterflies and hummingbirds.