How to Grow and Care for the Black Dahlia Plant
Learn to cultivate the deep, velvety tones of 'black' dahlias. This guide offers key steps for successfully growing and preserving these striking, dark-hued blooms.
The presence of a near-black dahlia offers a unique visual appeal in a garden. These deep, velvety blooms create a sense of mystery and sophistication. Their contrast against bright green foliage makes them a focal point in any floral arrangement or landscape design, adding depth and an unexpected element to the garden’s color palette.
The Reality of Black Dahlias
While the idea of a truly black flower is captivating, one does not exist in the dahlia world. Plants marketed as “black” are displaying shades of deep burgundy, dark maroon, or rich red. This optical effect is due to high concentrations of pigments called anthocyanins, which absorb most visible light, creating a color that appears black.
Plants lack the genetic pathways to produce melanin, the pigment for black coloring in animals. Instead, they rely on concentrating other pigments, which is why even the darkest flowers often reveal undertones of red or purple in direct sunlight.
Popular Black Dahlia Varieties
- ‘Arabian Night’ produces deep, rich red flowers that appear almost black in low light. Its formal decorative form features broad, flat petals, and this variety grows to about three to four feet in height.
- ‘Black Cat’ (also known as ‘Chat Noir’) is a cactus-type dahlia with distinctive spiky petals that are a deep, velvety red-black. The blooms reach about six inches in diameter on plants that can grow up to four feet tall.
- ‘Karma Choc’ offers dark chocolate-maroon flowers on a plant well-suited for container gardening. Part of the Karma series, it was bred for the cut flower market and has long, strong stems and an excellent vase life.
- ‘Black Jack’ is an impressive variety, featuring large, informal decorative blooms that can reach up to eight inches across. Its petals are a deep wine-red, and this tall variety requires staking to support its massive flowers.
How to Grow Black Dahlias
Successful cultivation begins with planting in the spring, once all danger of frost has passed and the soil has warmed to at least 60°F (15.5°C). Dahlia tubers should be planted in a location that receives full sun, meaning at least six to eight hours of direct sunlight per day. The soil must be well-draining; amending heavy clay soils with compost or sand can improve drainage. Plant the tubers about six inches deep, laying them horizontally with the “eye” or growing point facing upwards.
Consistent moisture is important for healthy growth. Water the tubers lightly after planting and then more regularly once shoots appear above the ground. During hot, dry periods, a deep watering two to three times per week will keep the soil evenly moist but not waterlogged. A layer of mulch can help retain soil moisture.
To encourage prolific blooms rather than excessive foliage, use a fertilizer that is low in nitrogen. A formula for tomatoes or a bloom-boosting fertilizer is a suitable choice. Begin feeding when the plants are about a foot tall and continue every few weeks through the growing season.
Many dahlia varieties require physical support to prevent their stems from snapping. It is best to place a stake in the ground at the time of planting to avoid damaging the tuber’s root system later. As the plant grows, loosely tie the main stem to the stake at regular intervals.
Overwintering Dahlia Tubers
In climates where the ground freezes, dahlia tubers must be dug up and stored for the winter as they are tender perennials and will not survive. The process should begin after the first hard frost has killed the plant’s foliage, which signals the tuber to enter dormancy.
Carefully lift the tuber clump from the ground with a garden fork, taking care not to damage the necks connecting the tubers to the central stem. Gently shake off excess soil and cut the stalk down to about four to six inches. Do not wash the tubers, as this can introduce moisture that leads to rot.
Allow the tubers to cure for several days in a dry, protected location like a garage, turning them upside down to drain moisture from the hollow stems. Once cured, place the tubers in a cardboard box or crate and cover them with a medium like peat moss, sand, or sawdust. Store the box in a cool, dark place where temperatures remain between 40-50°F.