How to Grow and Care for Rhubarb and Custard Dahlia

The Rhubarb and Custard dahlia is a collarette type, known for its distinctive and charming appearance. Its flowers feature a single row of broad outer petals in a blend of creamy, pale peach tones with a raspberry-pink base. Encircling the bright yellow center is a frilly collar of smaller, blush-pink or creamy-white petals. This variety grows to a height of 70 to 90 centimeters, forming a compact, bushy plant well-suited for garden borders or large containers. The blooms are around 10 to 15 centimeters in diameter and appear from mid-summer until the first frosts.

Planting Rhubarb and Custard Dahlias

Successful cultivation begins with planting in spring, after all danger of frost has passed and the soil has started to warm. These plants thrive in full sun, requiring at least six to eight hours of direct sunlight each day to produce strong stems and abundant flowers. A spot sheltered from strong winds is also beneficial, as the stems can become heavy with blooms later in the season.

Healthy root development requires proper soil preparation. Dahlias need well-drained, fertile soil to prevent their tubers from rotting. Before planting, amend the soil by incorporating organic matter such as well-rotted compost or manure. This practice improves both the soil’s structure for better drainage and its nutrient content.

To plant, dig a hole approximately 15 cm deep and place the tuber inside with the “eye,” or growth bud, pointing upwards. If planting multiple tubers, space them 45 to 60 cm apart to ensure each plant has adequate air circulation and room to grow. After covering the tuber, water lightly to settle the soil, but avoid heavy watering until sprouts appear.

Seasonal Care and Maintenance

Once your dahlia has sprouted and begins its summer growth, consistent care will ensure a spectacular display of flowers. Water deeply and regularly, once or twice a week, to keep the soil consistently moist but not saturated. Applying a layer of mulch can help retain soil moisture and regulate temperature.

Regular feeding fuels abundant blooming. Use a balanced, low-nitrogen fertilizer, such as a 10-10-10 formulation, applied monthly throughout the growing season. High-nitrogen feeds should be avoided as they encourage lush foliage at the expense of flower production.

As the plant grows taller, providing support is important to prevent the heavy-flowered stems from bending or breaking. Insert a sturdy stake near the base of the plant at planting time or shortly after, and loosely tie the main stem to it as it grows. Staking early prevents later damage to the tuber and root system.

A pruning technique known as “pinching” can lead to a fuller, bushier plant with more flowers. When the dahlia reaches about 30 cm in height and has developed several sets of leaves, pinch off the central growing tip. This encourages the plant to branch out from the lower leaf nodes for a more robust structure.

Overwintering Dahlia Tubers

For gardeners in regions with cold winters, lifting and storing the tubers is needed to preserve the dahlia for the following season. This process begins after the first hard frost in the fall, which will blacken the plant’s foliage. Cut the stalks down to about 10 to 15 centimeters from the ground.

Wait about a week or two after cutting back the foliage before digging up the tubers. Use a garden fork or spade, starting well away from the plant’s base to avoid accidentally piercing the delicate tuber clump. Gently lift the entire clump from the soil and shake off any excess dirt, being mindful not to break the slender necks that connect individual tubers.

Once lifted, the tubers need to be cured to prepare them for storage. Place them in a dry, well-ventilated location that is protected from frost, such as a garage or shed, for a couple of weeks. This allows the skins to toughen and any cuts to heal, which helps prevent rot during storage.

For winter storage, place the cured tubers in a box or crate filled with a loose, insulating medium like sand, peat moss, or vermiculite. Ensure the tubers are completely covered and not touching each other to promote air circulation. Store the container in a cool, dark, and frost-free location where temperatures remain between 4 and 10 degrees Celsius.

Common Pests and Diseases

Slugs and snails can be particularly damaging to young dahlia shoots, so it is important to employ controls early on. Earwigs and aphids are also frequent pests. Aphids can be managed with insecticidal soap, while earwigs can often be trapped and removed.

Powdery mildew is one of the most common issues affecting dahlias, appearing as a white, dusty coating on the leaves, especially in humid weather. To prevent it, ensure good air circulation by spacing plants properly and avoid overhead watering that leaves foliage wet. If mildew does appear, promptly remove affected leaves and consider applying a fungicide to manage its spread.