Dahlias, with their lush, vivid blossoms, are a garden favorite and often take front and center at county and state fair competitions. Unfortunately, they are semi-tropical plants and will not overwinter in Kentucky’s climate. Don’t worry, though. With a little effort in storing their tuberous roots properly, you can enjoy your dahlias year after year—and maybe bring home a blue ribbon or two in the process.
Dig only your healthiest plants. Roots from any plant that may have shown signs of a virus should end up in the trash. Virus symptoms may include streaked or mottled foliage, distorted leaves or flowers, or stunted growth. You do not want disease to spread among your healthy dahlias next year. While some people dig their dahlias before the first frost, it is often best to allow them more time in the ground to mature as much as possible. Though a frost may damage top foliage and blooms, roots will continue to mature and toughen up through a light frost and often through the first hard freeze, depending on how deep into the soil that freeze went.
Cutting the tops off a few days before digging the tuberous roots will allow the eyes to come out, which makes it easier to accurately divide the clumps. Water is a tuberous root’s enemy, so many people will cover the freshly cut tops with aluminum foil to prevent water from getting into the crown until they can dig them.
Be careful when digging and handling the tuberous roots. Dig into the soil on all four sides of a clump, about 12 inches from the stalk. Using either a shovel or fork, gently lift the clump, then turn it upside down to drain any water from the stalk. If you lift them in the morning and leave them out to air dry for a couple of hours, they will not be as fragile. Then, using a hose, you can wash off the dirt without damaging the tubers.
The clump of roots could be stored as is, but it is usually easier to divide the clumps in the fall when they are softer. If left to spring, some clumps can become so hard they can be almost impossible to cut. Remove all the small feeder roots and stems, which can promote root rot during storage. When you cut the clumps, look for the eyes. Each division should have a crown with an eye. If the inside of the crown shows brown or rusty spots, cut those away. Those spots probably indicate crown rot, and the tuberous root will not make it through the winter. To avoid spreading virus between plants, dip your cutting tools into a solution of one-part bleach and 10-parts water or spray them with a disinfectant after dividing each clump.
After making each division, dip the cut ends into a fungicide and let dry. Drying time will depend on temperature and humidity but could take between 24 and 36 hours depending on the size of the cut.
Store your tuberous roots in a medium that maintains a decent, but not excessive moisture level. Storing tubers in coarse vermiculite in a plastic bag is one of the preferred methods. Check occasionally to ensure rotting is not occurring and mice or other rodents have not compromised your dahlia stash.
For more information, contact the Carter County office of the UK Cooperative Extension Service. Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of economic or social status and will not discriminate on the basis of race, color, ethnic origin, national origin, creed, religion, political belief, sex, sexual orientation, gender identity, gender expression, pregnancy, marital status, genetic information, age, veteran status, or physical or mental disability.