Delphinium Black Knight

Dark-Flowered Perennial

Black Knight delphinium is dolphin-shadped. The word delphinium is related to dolphin.
David Beaulieu

"Larkspur" is a common name for the genus, Delphinium. But the scientific name is so widely employed that it doubles, in essence, as a second common name (when used in this fashion,we do not capitalize). The taxonomy of the particular kind we cover below is Delphinium 'Black Knight'. The cultivar name 'Black Knight' is apt (see below).

Plant Type

Black Knight delphiniums are herbaceous perennials. Because of the plant's dark purple flowers, you may be surprised to learn that it is in the Buttercup family, a plant family associated with the color, yellow. However, upon inspecting the foliage, you will see the family resemblance.


The deeply dissected leaves, slightly reminiscent of maple leaves, may help with family identification, but growing this perennial is all about the blossoms. Tightly-packed spikes of semi-double, dark purple flowers reach to the sky, making a bold statement in the landscape. It could not be otherwise for a plant so tall (mine reached about 7 feet) with flowers of such a striking color. Plants bloom in mid-June or early July in my zone 5 garden.

Black Knight Delphinium is no wallflower, no mousy little perennial that only a plant collector could love; it is, rather, a plant that screams, "Notice me!"

Planting Zones for 'Black Knight' Delphinium

The various members of the Delphinium genus are indigenous plants spread out across the Northern Hemisphere. That Black Knight claims native status in these regions, specifically, should not surprise us since in the landscape they perform so much better in areas where summertime heat waves are more the exception than the norm. Black Knight delphiniums are suited to planting zones 3-7. Some gardeners mulch them for winter protection but do be aware that crown rot can be a problem for these plants, so some experts suggest focus affording them optimal drainage in winter rather than mulching them. If you do apply mulch, keep it away from the crown.

Sun and Soil Requirements

Plant these tall perennials in full sun. Grow Black Knight Delphinium in well-drained soil. Add soil amendments for optimal growth. For example, fertilizing regularly with compost will aid in their growth.

Uses for 'Black Knight' Delphinium

Along with hollyhocks and foxgloves, delphiniums are classic cottage garden plants for use in the back row of a mixed flower bed. Used by themselves, en masse, they can form a border or soften the look of a fence.

Larkspurs Attract the Right Kind of 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:

That's what we call drawing the right kind of crowd!

Care for 'Black Knight' Delphinium

All of these benefits do not come without a cost, though. As tall, floppy plants, Black Knight Delphiniums require staking. Without staking, stalks snap easily in high winds. Some growers also cut them down to the ground after blooming, in an attempt to foster re-blooming in early autumn. As one of the Pacific hybrids, 'Black Knight' does not succumb to powdery mildew as easily as other types.

No matter how much care you give them, larkspurs 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.

Outstanding Features

The cultivar name, 'Black Knight' was chosen with this plant's most outstanding feature in mind: its flowers are a dark purple. Speaking of the cultivar name, do not confuse it with the butterfly bush named 'Black Knight.'

But flower color is only part of the story. First of all, the flowers are also densely packed on their spikes. Secondly, on a shorter plant, the color would not be so easily displayed to optimal impact. This perennial's NBA-worthy height must also be considered one of its foremost qualities, consequently. Of course, its tallness is something of a double-edged sword, since it makes staking necessary.

More on Delphinium Plants

We had a rather special introduction to delphiniums in our life. One of the first times we ever spotted a hummingbird, the tiny jewel was buzzing around a delphinium. While we cannot say that we have had numerous such sightings since then, the experience has always stayed with us.

Delphinium plants come in a wide variety of colors, including white, pink and various shades of blue. Our favorite—since it is relatively rare to find blue flowers that are a sky-blue (morning glory comes to mind) —is the aptly named 'Sky Blue.' The species nudicaule adds a red-colored type to the landscaping palette, while 'Sungleam' bears yellow flowers.

The story behind the plant's name is rather interesting. The word, Delphinium comes from the Greek for "little dolphin." Are you scratching your head over that one? Well, the reference is to the bottle-like shape of the unopened flowers, which is reminiscent of the shape of a dolphin's nose. If you wish to check for yourself, scrutinize the image we've provided above. Personally—if we're going to use our imaginations to declare what the unopened flowers look like—we're more inclined to say that they look like little fish. One is reminded of the derivation of the name, "​Columbine," which also appeals to an alleged resemblance to a member of the animal kingdom.​