Dear Aggie, I had beautiful dahlias this summer. Can I store them over the winter for next year?
Dahlias are one of the jewels of the summer landscape. Their flowering peaks in late summer, filling the garden with cheerful colors ranging from red to yellow to purple. Although a perennial in warmer climates, northern country dahlias are not hardy and will need digging before the ground freezes in the fall. Tubers must be carefully stored over the winter so they can be replanted only after the warmer weather in spring.
Like potatoes, dahlias form underground tubers. Gardeners should dig dahlia tubers as soon as the first frosts have smothered the foliage, but before the ground freezes. Begin by cutting away all leaves, leaving four to six inches of stem above ground level. You can then leave the plants in the ground for a few more weeks, which allows “eyes” (next year’s growth points) to form underground. However, it is crucial that the tubers are lifted before the ground itself begins to freeze.
A fork is the ideal tool for lifting the tubers, although a shovel can be used. Loosen the soil around the plant about three to four inches from the main stems. Once loosened, gently lift the entire plant. You can remove any remaining dirt by gently brushing it away. Some growers choose to leave some soil on the tubers.
When digging the tubers, care must be taken not to cut or break them off from the main plants. If damaged, disease can invade and cause rot during winter storage. Be sure to leave a short stalk on each bulb or group of bulbs; These provide the growth point for next season’s growth. Tubers broken off without this growing point will eventually rot.
Dahlias are easiest to divide in the fall just prior to storage, although this can also be done in the spring before planting. This is often easier after all soil has been carefully removed by washing the tubers with water from a hose. Examine each lump carefully. Sometimes you will see individual plants with individual stems that can be carefully plucked from the larger clump. If not, you can split large crowns by clipping them apart. Use a sharp knife to divide large single stems into multiple plants. A piece of the stalk – the growth point – must remain attached to the tubers in order for them to grow. Disinfect the knife with alcohol between plants to avoid spreading disease.
Spread the tubers out to dry. Once dry, place them in wooden crates or boxes containing either peat moss, wood shavings, shredded newspaper, or a combination of these. Avoid plastic storage boxes with lids; these hold too much moisture and encourage rot. Be sure to label each with the variety and color. Store the boxes in a cool, dark place protected from frost. The ideal storage temperature is 40F with moderate humidity. You don’t want the tubers to rot from excess moisture or dry out from too little. Root cellars are ideal; However, garages and basements will do. Watch for signs of mice in winter as they will eat the tubers. Stored tubers can then be taken out of storage for planting next spring.
Written by Michael Nuckols, Director of Agriculture and Natural Resources, Cornell Cooperative Extension