Dahlias produce blooms from mid-summer until the first frost. These plants are grown from structures commonly referred to as bulbs, but they are botanically classified as tuberous roots, functioning as underground storage organs. These storage roots multiply significantly during a single growing season, allowing a single planted tuber to yield a substantial increase in planting stock for the following year.
How Dahlia Tubers Grow and Multiply
The multiplication of dahlias is an annual process. When a dahlia tuber is planted, it acts as the “mother tuber” and initial energy reserve for the season. Throughout the growing period, the plant produces a cluster of new, swollen storage roots that radiate from the base of the stem, forming a clump.
Each new structure is a distinct tuber designed to store energy for dormancy and subsequent spring growth. A viable tuber hinges on three parts: the fleshy body, the neck, and the crown. The crown is the point where the tuber joins the stem, and it is the only area that produces “eyes.”
An “eye” is a small growth point that will develop into the new plant’s sprout. For a separated tuber to grow, it must have an intact neck connecting the storage body to a piece of the crown containing at least one viable eye. A single healthy plant can produce five to twenty new tubers in one season.
Proper Timing for Harvesting Tuber Clumps
Harvesting begins after the growing season concludes with a hard frost. The frost signals the plant to channel energy from the foliage into the newly formed tubers. This movement of energy is a natural curing process that prepares the storage roots for winter dormancy.
After the foliage has been killed by the frost, the stems should be cut back, leaving about six inches above the soil line. Wait one to two weeks before digging up the clumps. This waiting period allows the protective skin of the tubers to toughen and moisture to drain away from the crown, reducing the risk of rot.
When lifting the clump, insert a garden fork about a foot away from the main stem to avoid puncturing the tubers. Gently loosen and pry the entire clump from the soil, taking care not to damage the necks. Once lifted, the clump should be labeled and allowed to dry in a cool, sheltered area for a few days so excess soil can be brushed off.
The Art of Dividing Tubers for Replanting
Division is the primary step in propagating dahlias, transforming one large clump into multiple viable plants. The goal is to separate the tubers while ensuring each new division can grow. Division is often done in the spring when the eyes begin to swell and become more visible, though fall division is also common for space-saving storage.
The clump should be thoroughly washed and examined to identify the crown area where the eyes are located. Using a clean, sharp knife or shears, carefully section the clump, ensuring each severed tuber retains a piece of the crown and at least one healthy eye. The neck connecting the tuber body to the crown must remain unbroken, as a snapped neck means the tuber cannot support a new sprout.
Discard any tubers that are thin, shriveled, lack a clear eye, or show signs of rot, such as soft or discolored sections. If a tuber is cut or damaged during digging, the wound can be dusted with a fungicide or sulfur powder to prevent disease.
Essential Steps for Winter Storage
Once the tubers are divided, they must be stored correctly to survive the winter. The primary factors to control are temperature and humidity; too much moisture causes rot, and too little leads to dehydration and shriveling. An ideal storage temperature is consistently cool, ranging between 38 and 50 degrees Fahrenheit, and the location must be frost-free.
The tubers should be packed in a medium that provides insulation and regulates moisture without becoming saturated. Common materials include coarse vermiculite, peat moss, or wood shavings. These mediums should be slightly moist, not wet, and used to surround the tubers in a crate or cardboard box, preventing them from touching one another.
Check the stored tubers periodically, approximately once a month, throughout the winter. Tubers that have become soft or mushy should be removed immediately to prevent the spread of rot. If tubers appear shriveled or wrinkled, the storage medium is too dry and needs a light misting to increase the humidity level.