Dahlias are popular garden plants known for their vibrant, diverse blooms that last from mid-summer until the first frost. These flowers are grown from tuberous roots, and their status as a perennial or an annual often confuses gardeners in colder climates. The question of whether these plants will return depends entirely on the climate they are planted in. For gardeners in Ohio, understanding the dahlia’s specific hardiness requirements is necessary for successful cultivation year after year.
Understanding Dahlia Hardiness and Ohio Zones
The direct answer to whether dahlias are true perennials in Ohio is no. Dahlias are native to the high-altitude regions of Mexico and Central America, making them tender tubers that cannot withstand freezing soil temperatures. They are reliably perennial only in warmer climates, specifically USDA Plant Hardiness Zones 8 through 11.
Ohio generally falls within USDA Hardiness Zones 5b to 6b, meaning the average extreme minimum winter temperatures range from -15°F to 0°F. Since the soil in Ohio gets far too cold for them to survive the winter unprotected, gardeners must treat dahlias as annuals or perform the labor-intensive process of lifting and storing the tubers each fall.
Preparing and Lifting Tubers for Storage
The process of preparing dahlia tubers for winter storage begins immediately after the first hard frost, which signals the plant to enter dormancy. A hard frost will cause the foliage to turn black, indicating that the plant’s energy has been redirected down to the tubers for storage. Gardeners should wait approximately one to two weeks after the foliage has blackened before digging, which allows the tuber skins to toughen and cure, improving their viability in storage.
Before lifting, the stalks must be cut back, leaving a stem handle of about four to six inches above the soil line. When digging, use a garden fork or shovel to loosen the soil in a wide circle, about a foot away from the main stalk, to avoid spearing the clump. Once the clump is carefully lifted, gently brush off excess soil. Place the clump upside down for a few days to drain any moisture from the hollow stem. This initial curing should take place in a cool, dry location out of direct sunlight, ensuring the tubers are dry to the touch before long-term storage.
Managing Dormancy During Winter Storage
Successful long-term storage requires mimicking the cool, stable conditions of their native environment, where the soil is cold but never frozen. The ideal storage temperature range is consistently between 40°F and 45°F, with a humidity level around 85%. Temperatures that are too high will encourage premature sprouting, while temperatures below freezing will destroy the tubers.
Storage locations such as a cool basement, root cellar, or insulated garage that stays above freezing work best. The cured tubers should be nested in a moisture-retaining medium like peat moss, vermiculite, or wood shavings within a container. Ensure the tubers do not touch each other, which prevents the spread of potential rot. Check on them monthly throughout the winter. If the tubers appear shriveled, the storage medium is too dry, and if they show signs of mold or rot, the environment is likely too warm or too humid, requiring a quick adjustment.
Replanting and Dividing Tubers in Spring
The final step in the dahlia’s annual cycle is the transition back to the garden in the spring. Ohio gardeners should hold off on planting outdoors until the danger of the last frost has completely passed and the soil temperature reaches at least 60°F. This timing usually corresponds to mid-to-late May in the region. To get a head start, tubers can be brought out of storage and potted indoors four to six weeks before the last expected frost.
Before planting, the overwintered clumps should be divided, as this increases the number of plants and reduces the risk of rot. The requirement for a viable division is that each individual tuber must have an “eye,” a small, visible bump or sprout located at the crown where the tuber connects to the old stem. Tubers without an eye will not sprout.