Dividing dahlia tuber clumps into individual tubers is an easy way to increase your dahlia stock. One healthy plant can produce up to 20 new tubers in a single growing season and each individual tuber will produce a clone of the parent plant.
Tubers come in all shapes and sizes and vary by variety. Some dahlia varieties produce plump, round tubers while others produce long, thin tubers. The size and shape of a tuber doesn'tdetermine the plants health, vigor, or bloom quality. Instead, tuber viability is based on each division having a body, intact neck, and crown with an eye. The eye turns into the sprout, the body holds the energy and nutrients needed to produce next year's plant, and the unbroken neck connects these two parts. If any of these parts are missing the tuber won’t grow.
It’s easiest to divide dahlia tuber clumps in the spring. At this time, the eyes start to swell making it clear where to cut. Begin by pulling your tubers out of storage and washing off any remaining soil. Then sterilize your pruners in a solution of one part bleach to ten parts water to avoid the spread of disease. It’s recommended to sterilize before you begin and between every dahlia clump.
Now that the tuber clump is washed, and the pruners are sterilized you can start dividing. First, cut the tuber clump in half to make it more manageable. Then cut off any rotten and damaged tubers. Remove any tubers with broken necks as none of these will be viable. Now that only healthy, viable tubers remain separate the clump into individual tubers by slicing vertically through the crown.
This can feel scary at first, but the process becomes easier with experience. Just remember that each division must have a body, intact neck, and piece of the crown with an eye to be viable.
If you’re having trouble identifying the eyes you can instead divide a clump into four sections. Using a knife or sharp pruners make two opposing vertical cuts in the central stem of the tuber clump. This will leave you with four quarters and each section will have a few tubers. More likely than not there will be an eye in each section.
Once your tubers are divided allow them to dry for 8 to 24 hours so the cutting wounds can callus over. Don’t let them dry for longer than 24 hours as this will cause them to shrivel and dry out.
Dahlia tubers should be planted outside after the last frost has passed. In areas without a frost, dahlias should be planted when nighttime low temperatures reach 50 degrees F. Depending on your growing location and situation you can either put the tubers back into storage, start the tubers early in the pots, create dahlia cutting beds, or plant the tubers outside.
Want to learn more about dividing dahlia tubers? Watch this step-by-step tutorial.