Dahlias are popular garden flowers known for their diverse forms, sizes, and colors. Specific techniques can advance their growth, ensuring early blooms and robust plants. By providing optimal conditions, gardeners can cultivate healthier plants and enjoy a more abundant flowering season.
Giving Dahlias an Early Start
Starting dahlia tubers indoors provides a significant advantage, promoting earlier blooms and stronger plants once transplanted outside. This process begins in late March or early April, approximately six to eight weeks before the last anticipated frost date in your area. This head start is beneficial as some dahlia varieties require a long growing season to produce flowers.
To begin, gather necessary supplies: various-sized pots (at least 4-inch diameter or larger with drainage holes), a well-draining potting mix, and optional heat mats and grow lights. Fill containers halfway with potting mix. Place a dahlia tuber horizontally or vertically, ensuring the eye (where new growth emerges) faces upwards or is exposed. Cover the tuber with 1 to 2 inches of soil, leaving the crown or eye visible if planted vertically.
Avoid immediately watering the soil; instead, wait until eye development is visible. Cool, damp soil can cause tubers to rot. Maintain a consistent soil temperature of at least 65°F (18°C), which can be achieved with a heat mat.
Once sprouts emerge, provide adequate light by placing them in a sunny window or under artificial grow lights. Dahlias require at least six hours of sunlight daily, and artificial lights should be kept on for 14-16 hours a day. As the plants grow, adjust lights to remain about six inches above the foliage. Before transplanting outdoors, after all danger of frost has passed, harden off the plants. Gradually acclimate them to outdoor conditions over a week to ten days, starting with short periods in a protected, cloudy location and slowly increasing exposure to sun and wind.
Advanced Care for Peak Performance
Once dahlias are established in the garden, specific care techniques can enhance their growth and bloom quality.
Pinching
Pinching, or “topping,” encourages bushier plants with more flowers. Do this when the plant is 8 to 16 inches tall and has at least three to four sets of leaves on the main stem. Remove the uppermost sprout or main growing tip just above a set of leaves using fingers or clean snips. This redirects the plant’s energy from vertical growth to developing lateral buds, resulting in multiple stems and a more robust plant. While it may delay the first flowers by a week or two, it leads to more blooms.
Disbudding
Disbudding is another technique used to achieve larger blooms, particularly for exhibition or cut flower purposes. This involves removing the smaller side buds that form alongside the main terminal bud on a flowering stem. By removing these competing buds, the plant concentrates its energy into the central bud, allowing it to develop into a larger, higher-quality flower.
Supporting
Supporting dahlias is important, especially for taller varieties or those with large, heavy blooms, as their stems can be brittle and prone to breaking. Individual stakes (wood, bamboo, or metal), about 6 feet tall, should be pounded into the ground at least 12 inches deep, 3 inches away from the plant’s center to avoid damaging tubers. As the plant grows, tie the main stems loosely to the stake, allowing for movement. For multiple plants, the “corral method” uses stakes placed every 3 to 4 feet along rows, with twine strung around them to support the plants.
Fertilizing
Fertilizing is important for promoting continuous bloom. Dahlias benefit from fertilizers that support flowering rather than excessive foliage growth. After initial planting, a balanced slow-release fertilizer can be incorporated. During the growing season, a fertilizer with lower nitrogen and higher phosphorus and potassium (e.g., a 5-10-10 or 10-20-20 blend) encourages bloom production. Fertilize every 3-4 weeks, or as recommended by the product, especially when plants are actively flowering.
Protecting Your Dahlia Investment
Protecting dahlias from common garden threats and ensuring their survival through winter is important.
Common pests include aphids, which can be managed with strong sprays of water or insecticidal soap. Powdery mildew, a fungal disease, appears as white, powdery spots on leaves and can be mitigated by ensuring good air circulation around plants and using organic fungicides like neem oil. Prompt identification and treatment help maintain plant health.
Preparing dahlias for winter is an important step in colder climates. After the first light frost blackens the foliage, but before a hard freeze, dig up the tubers. Cut stems back to 4-6 inches above ground before carefully lifting the entire clump, avoiding damage to tubers. After digging, gently remove excess soil from the tubers. Tubers then need to cure for a few days in a cool, dry place out of direct sunlight, allowing the skin to toughen.
For winter storage, ideal conditions are a cool, dark, and frost-free environment with consistent temperatures between 38-50°F (3-10°C) and high humidity (75-90%). If humidity is too low, tubers can shrivel and dehydrate; excessive humidity risks mold and rot. Store tubers in materials like peat moss, vermiculite, wood shavings, or sawdust to regulate moisture. Place tubers in breathable containers such as cardboard boxes, plastic bins with ventilation holes, or mesh bags. Regularly check stored tubers throughout winter, removing any that show signs of rot or mold to prevent spread.