Dahlia ‘Thomas’ is a highly regarded dahlia variety, celebrated for its opulent blooms and striking presence in garden settings. Its visual appeal makes it a favored selection among both seasoned gardeners and those new to cultivating dahlias. This cultivar brings dramatic beauty to any landscape, drawing admiration for its vibrant display.
Understanding Dahlia ‘Thomas’
Dahlia ‘Thomas’ is classified as a decorative dahlia, often reaching dinnerplate size. These flowers typically measure 6 to 8 inches in diameter, characterized by fully double forms that lack a central disc. The petals are broad, flat, or sometimes slightly rolled, arranged in a regular, symmetrical pattern.
Its distinguishing feature is a deep, rich purple hue, often darker towards the center, which can appear luminous in direct sunlight. The plant exhibits a bushy, upright growth habit, generally reaching 3 to 4 feet (90-120 cm) tall and spreading 18-24 inches (30-60 cm). It blooms from mid-summer until the first frost, providing long-lasting color.
Planting Your Dahlia ‘Thomas’
Planting ‘Dahlia Thomas’ tubers should occur in spring or early summer, after all danger of frost has passed and the soil temperature consistently reaches at least 60°F (15°C). Dahlias thrive in full sun, ideally six to eight hours of direct sunlight daily. While they can tolerate some partial shade, especially in hotter climates, too much shade can lead to leggy growth and fewer blooms.
Dahlia tubers require well-draining soil, as they are susceptible to rot in waterlogged conditions. Amending heavy clay soils with organic matter such as compost, peat moss, or well-rotted manure can improve drainage and fertility. A soil pH between 6.0 and 7.0, which is slightly acidic to neutral, is suitable. Dig a hole approximately 4 to 6 inches deep and wide enough to comfortably accommodate the tuber.
Place the tuber horizontally in the hole with the “eye” or sprout facing upwards. If planting multiple tubers, space them about 24 to 36 inches apart to allow for their mature size and adequate air circulation. After placing the tuber, cover it with a few inches of loose, compost-rich soil. Avoid watering immediately after planting unless the soil is exceptionally dry, as too much moisture before sprouts emerge can encourage tuber rot. Once shoots appear, you can begin regular watering.
Caring for Dahlia ‘Thomas’ During the Growing Season
During the active growing period, ‘Dahlia Thomas’ requires consistent moisture. Water deeply one to two times per week, increasing frequency during hot, dry spells to keep the soil consistently moist but not waterlogged. Mulching around the plants helps retain soil moisture, regulate temperature, and suppress weeds. Fertilization is important for vigorous growth and abundant blooms.
Dahlias benefit from a balanced fertilizer or one that is low in nitrogen, such as a 5-10-10 or 0-10 formulation, to promote flower production over excessive foliage growth. Apply fertilizer every 2 to 3 weeks or monthly, starting about 30 days after planting. Due to their tall stature and large blooms, staking is often necessary to prevent stems from breaking, especially in windy conditions. Install stakes early in the season when plants are young to avoid damaging the tubers later.
Deadheading, which involves removing spent flowers, encourages the plant to produce more blooms throughout the season. Cut the faded flower stems back to the base to promote continuous flowering. Monitor for common garden pests like aphids or spider mites, and diseases such as powdery mildew. Ensuring good air circulation around the plants can help prevent fungal issues.
Winter Care for Dahlia ‘Thomas’ Tubers
In colder climates (USDA Hardiness Zones 3-7), ‘Dahlia Thomas’ tubers must be lifted from the ground and stored indoors to protect them from freezing temperatures. The optimal time to dig them up is after the first hard frost has blackened the foliage, signaling the plant to go dormant. Waiting about 10 to 14 days after this initial frost allows the tubers to cure and toughen their skin.
To lift the tubers, carefully cut the stems back to about 4 to 6 inches above the soil line. Use a garden fork to gently loosen the soil in a wide circle around the plant, being cautious not to damage the tubers. Once lifted, gently brush off any excess soil; avoid rinsing, which can introduce too much moisture before storage. Allow the tubers to air dry in a cool, dark, and well-ventilated area for several days to a week to cure properly.
After curing, store the tubers in a cool, dark, and frost-free location where temperatures remain consistently between 40°F and 50°F (7°C and 10°C). Store them in peat moss, vermiculite, or dry sand, placed in ventilated cardboard boxes, paper bags, or plastic storage tubs with loose lids. This helps retain some moisture while allowing for air circulation, preventing both shriveling and rot. Periodically check the tubers throughout winter for any signs of mold, rot, or excessive drying, adjusting storage conditions as needed.