The ‘Downham Royal’ dahlia is a stunning variety, providing rich, saturated color from mid-summer until the first frost. Classified as a Ball or Miniature Ball dahlia, its fully double blooms have tightly inrolled petals that form a flattened, globular shape, typically measuring 7 to 10 centimeters across. The color is a deep, iridescent magenta or reddish-purple, contrasting dramatically with the mid-green foliage. This tuberous perennial grows 0.9 to 1.2 meters tall, making it an excellent choice for garden borders and a highly sought-after cut flower.
Selecting the Site and Initial Planting
Choose a location that receives a minimum of six to eight hours of direct sunlight daily. Ample sun exposure supports robust growth and maximizes flowering potential. The ideal soil should be well-drained and fertile, as tubers are prone to rot in cold, soggy ground.
Planting should occur in the spring after the last frost date has passed and the soil temperature is above 60 degrees Fahrenheit. Dig a hole 4 to 6 inches deep and lay the tuber horizontally. Ensure the eye—the small, bud-like growth point near the neck—is facing upward. The neck must remain intact for the plant to grow.
Gently backfill the hole, completely covering the tuber. Avoid watering immediately unless the soil is exceptionally dry, as overwatering can cause the tuber to rot before roots develop. Space individual tubers 18 to 24 inches apart to ensure good air circulation and prevent disease.
Essential Summer Maintenance
Once green shoots are visible, a consistent maintenance schedule encourages abundant blooms. During dry weather, begin deep watering, providing enough moisture to soak the root zone thoroughly. Allow the soil surface to dry slightly between waterings.
Due to the plant’s height, staking or caging should be implemented at planting time to prevent wind or heavy blooms from snapping the brittle stems. The dahlia is a heavy feeder, requiring regular fertilization with a formula low in nitrogen but high in phosphorus and potassium. Use a fertilizer with an NPK ratio around 5-10-10 or 10-20-20, which promotes flower production over leafy growth.
Apply this fertilizer every three to four weeks, starting about 30 days after planting, to provide steady nutrients. To promote a bushier structure and increase flowers, pinch out the central growing tip once the plant reaches 12 to 18 inches tall. Deadheading spent blooms redirects the plant’s energy from seed production into creating new buds for continuous flowering.
Protecting Your Dahlia from Pests and Disease
The lush foliage and tender new growth attract common garden pests, requiring regular inspection. Slugs and snails damage young shoots, leaving irregular holes and slime trails. Control them using non-chemical methods like beer traps, copper barriers, or diatomaceous earth.
Aphids cluster on the undersides of leaves and new buds, causing distorted growth. Dislodge minor infestations with a strong jet of water, or apply insecticidal soap or neem oil for stubborn cases. Earwigs chew holes in petals and leaves; manage them by setting traps, such as a rolled-up damp newspaper placed near the plant.
Fungal issues like powdery mildew appear as a white, dusty coating on the leaves, especially in warm, humid conditions with poor air circulation. Prevention includes proper plant spacing and watering the soil directly instead of the foliage. If mildew appears, apply a diluted mixture of milk and water or an organic fungicide, and remove any heavily infected leaves.
Preparing Tubers for Winter Storage
The ‘Downham Royal’ is a tender perennial, so tubers must be lifted for winter storage in most climates, as they will not survive freezing temperatures. After the first hard frost kills the foliage, wait a few days to allow the plant to enter dormancy and the tuber’s skin to thicken. Cut the stems back to four to six inches above the soil line before digging.
Carefully lift the tuber clump using a garden fork, starting well away from the main stem to avoid damaging the neck. Gently shake off the majority of the soil, but avoid washing them, as surface moisture encourages rot during storage. Allow the tubers to cure in a cool, sheltered spot for a few days until the skin is dry to the touch.
Store the dried tubers in a well-ventilated container, such as a cardboard box or plastic crate. Layer them within a dry medium like peat moss, vermiculite, or wood shavings to maintain consistent humidity. The storage location should be dark, dry, and cool, ideally between 38 and 50 degrees Fahrenheit, to prevent sprouting or dehydration. Check the tubers monthly, misting the storage medium if they shrivel or removing any that show signs of mold or rot.