Dahlias are a favorite for summer gardens, but they require annual division to maintain their vigor. The dahlia plant grows from underground tuberous roots that multiply each season, forming a large, congested clump. Division separates these clumps into smaller, viable sections, rejuvenating the parent plant and propagating new stock. This asexual reproduction ensures each new plant is genetically identical to the original, preserving the variety’s characteristics.
Optimal Timing for Division
The best time to divide dahlia tubers is in the late winter or early spring, just before the typical planting season begins. This timing is ideal because the tubers have completed their dormant period and are beginning to awaken. The slight rise in temperature encourages the small growth buds, known as “eyes,” to swell and become visible near the crown.
The visibility of these eyes is essential, as a tuber piece cannot grow without at least one attached eye. Dividing too early, while the tubers are fully dormant, makes the eyes difficult to locate. Many gardeners complete division four to six weeks before the last expected spring frost date, allowing newly divided pieces to begin pre-sprouting indoors before planting outside.
Recognizing the Need for Division
Dahlia tubers multiply each growing season, forming a dense, interconnected clump of storage roots. Leaving the clump undivided for too long negatively impacts the plant’s performance. Generally, division should be performed every two to three years, though some vigorous varieties may benefit from yearly splitting.
The most noticeable sign that division is necessary is a decline in bloom quality, such as smaller flowers or weakened stems. An overly congested root ball forces tubers to compete for limited nutrients and space, diverting energy from flower production. Dividing the clump resets the growth cycle, allowing the plant to focus energy on fewer healthy storage roots, which encourages larger, more robust blooms.
Step-by-Step Guide to Dividing Tubers
Before beginning division, the tuber clump should be thoroughly cleaned of residual soil, often by washing it gently, to clearly expose the crown area. The crown is the point where the tubers attach to the main stem and where the growth eyes are located. Use a sharp, sterilized cutting tool, such as a knife or floral shears, to ensure clean cuts and prevent disease transmission.
The goal is to separate the clump into individual sections. Each piece must consist of a healthy, firm tuber attached to a portion of the crown containing at least one viable eye. The “neck,” which connects the crown to the tuber body, must remain intact, as a broken neck severs the energy supply from the growth bud.
Discard the mother tuber (the original one planted the previous season), which is often hollowed out or soft. Also discard any tubers that are shriveled, soft, or show signs of rot.
Start by removing the old, hollow main stem as close to the crown as possible, as this tissue retains moisture and can lead to rot. If the clump is large, cutting it in half first makes individual tubers more accessible. Carefully examine the crown for the small growth points, and make cuts to isolate each viable tuber, ensuring the eye remains attached to its section of the crown.
Post-Division Handling and Storage
Once separated, viable tubers require a brief period of curing before planting or long-term storage. Curing involves allowing the freshly cut surfaces to dry out and form a protective callus or seal. This process typically takes one to two days in a cool, dry, and well-ventilated location, which prevents the entry of pathogens that cause rot.
If the tubers will be stored before planting, the cut surfaces can be lightly dusted with a powdered fungicide or flowers of sulfur. This dusting acts as a barrier against fungal infections. If the divided tubers cannot be planted immediately, they should be placed in a slightly moist, non-soil medium like vermiculite or peat moss. Store them in a location that maintains a temperature between 40 and 50 degrees Fahrenheit, ensuring they do not freeze or dry out.