Black Knight Delphinium Plant Profile

Dark-Flowered Perennial

Black Knight delphinium bloom about to open.
Flower bud of Black Knight delphinium about to open. David Beaulieu

Delphiniums are hard not to notice in the landscape. They are members of the buttercup family, and, if you take a good look at the deeply dissected, maple-like leaves, you will see the family resemblance. But it is the impressive height and tightly-packed spikes of oddly-shaped flowers that gain delphiniums so much attention. The Black Knight cultivar sports semi-double, dark purple flowers. Grow Black Knight when a mousy little wallflower of a plant just won't do.

How to Grow Black Knight Delphinium

Delphiniums perform much better in areas where summertime heat waves are more the exception than the norm. Even then, they are fussier and require more maintenance than do many other perennials.

Delphiniums need full sun and more fertilizer than you may be used to giving your perennials. Select an area for them that is sheltered from high winds. Prepare the planting hole by mixing in compost.

As tall, floppy plants, Black Knight delphiniums require staking. Without staking, their stalks snap easily in high winds. Some growers also cut them down to the ground after blooming, in an attempt to foster reblooming in early autumn.

Some gardeners mulch them for winter protection. But do be aware that crown rot can be a problem for these plants. The risk of losing them in winter from poor drainage is greater than the risk posed by the cold. So it is better to focus on just giving them optimal drainage in winter rather than mulching them. If you do apply mulch, keep it away from the crown. Powdery mildew can also be a problem for delphiniums, but, as one of the Pacific hybrids, Black Knight does not succumb to powdery mildew as easily as some other types do.

No matter how much care you give them, they are not long-lived perennials. Even under the best of conditions, do not expect more than four years out of them (probably less). In warmer climates, they may be treated as annuals.

Light

Install your Black Knight delphinium in an area of your garden that receives a daily dose of six hours or more of direct sunlight.

Soil

Grow delphiniums in a humusy soil that drains sharply.

Water

Black Knight delphinium has average water needs.

Fertilizer

Apply a balanced fertilizer every 2 to 3 weeks from the time the plants emerge from the earth to the time they stop flowering.

Uses for Black Knight Delphinium

Let delphiniums aid you in achieving your ideal landscape color scheme. Delphinium plants come in a wide variety of colors, including white, pink, and various shades of blue. A favorite—since it is relatively rare to find blue flowers that are a sky-blue —is the aptly named Sky Blue. It helps you inject into the landscape a blue color similar to what you find in morning glory (Ipomoea tricolor Heavenly Blue).

The species nudicaule adds a red-colored type to the landscaping palette, while Sungleam bears yellow flowers.

Along with hollyhocks (Alcea rosea) and foxgloves (Digitalis spp.), delphiniums are classic cottage garden plants for use in the back row of a mixed flower bed. Used by themselves and planted in a mass, they can form a border or soften the look of a fence.

Delphiniums and Wildlife

If you tell someone whose garden has just been devastated by deer pests that a plant "attracts wildlife," you may very well get a very pointed question in return: "What kind of wildlife?" Fortunately, Black Knight delphiniums are deer-resistant plants. Bambi is no fool: These perennials are poisonous plants.

The wildlife they do draw is of a sort that is almost universally desired by gardeners:

Origin of the Name

The story behind the plant's genus name is rather interesting. The word, Delphinium, comes from the Greek for "little dolphin." The reference is to the bottle-like shape of the unopened flowers, which is reminiscent of the shape of a dolphin's nose. This is not the only case where a plant name comes from the plant's supposed resemblance to an animal. The name, "​Columbine," comes from the fact that the flowers of Aquilegia ssp. resemble doves.​