Issue: November 15, 2008
Storing dahlia roots over winter.
Santa Fe Master Gardeners received a relevant question at the Santa Fe Growers' Market - "We had an inquiry about storing newly dug dahlias through the winter so they can be replanted in the late spring. Frequently the tuberous roots rot in storage and have to be discarded." This is a good question for many New Mexico gardeners, so I will share their question and summarize the responses received from several Master Gardeners.
As one Santa Fe Master Gardener noted, she leaves hers in the ground through the winter in a warm microclimate (south side of a wall). She only needs to cover the roots with a thick layer of mulch to help maintain soil warmth and protect the bulbs. This will be an appropriate strategy for overwintering dahlias for gardeners in warmer parts of New Mexico and in warm microclimates. Other gardeners should dig the dahlias and store them through the winter.
Clean and dry the dahlia roots before storing. When drying the roots, do not dry them excessively; dry them enough to remove all surface moisture. If the roots dry excessively during the winter, they will not grow well in the spring. If the roots remain moist during storage, they will probably rot.
Some people recommended wrapping the cleaned, dried, roots in newspapers stored in a root cellar. Many New Mexico gardeners do not have a root cellar, but they can recreate the cool, humid conditions of the root cellar in other ways.
The roots may be stored in plastic bags, plastic tubs, or Styrofoam ice chests filled with a storage medium of very slightly dampened vermiculite, perlite, coarse organic mulch, or cedar shavings (pet bedding material). Place the dried roots into the plastic bag with the storage medium separating the roots so that the rotting of one root will not infect other roots. Place a layer of storage medium in the bottom of the plastic tub, then place a layer of dahlia roots on top of this layer in a manner that prevents the roots from touching each other. Then fill with another layer of storage medium and another layer of roots. The final filling layer should be the storage medium. Some gardeners place a layer of slightly damp newspaper on the top of the layered roots and storage medium.
You can store the roots in a garage, but they roots should not freeze. If freezing is likely in the garage the ice chest may be a way to provide additional protection from freezing.
During the winter inspect the stored roots periodically and remove any that are beginning to rot. When the weather begins to warm in the spring, you can plant your overwintered dahlia in well-prepared garden soil to which you have added compost and phosphate fertilizer.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!