One of the best ways to multiply your dahlia stock is to divide the tuber clumps into individual tubers. One healthy plant can give upwards of 20 new plants in a single growing season.
In late winter or very early spring, pull your dahlia tuber clumps out of storage and discard any tubers that are soft or have completely dried out. Wash off any remaining soil that was utilized during storage and sterilize your pruners to avoid spreading disease when you make cuts.
It’s easier to divide dahlia tubers in early spring since some of the eyes will start to swell and sprout. This makes it easier to determine where to cut. When determing where to cut remember that a tuber needs a body, unbroken neck, and eye to grow and reproduce. The body holds the energy and nutrients needed to produce next year's plant, the eye turns into the sprout, and the unbroken neck connects these two parts. If any of these parts are missing the tuber will not grow.
Start by cutting the tuber clump in half to make it more manageable. Cut off any mushy or damaged tubers. Then begin separating the clump into individual tubers by slicing through the crown with sharp pruners. This can feel scary at first, but the process becomes easier with experience. Just remember that a viable tuber must have a body, eye, and unbroken neck.