Overwintering Dahlias: 5 Tips for Overwintering Dahlias

Overwintering is the process of ensuring a plant survives the winter by protecting it from the cold and providing the extra light needed in the long, dim winter months. Ornamental plants, such as dahlias, feature flowers over the summer, but the blooms die off in cold weather. While treated in some colder climate zones as annuals, dahlia plants can be perennials and last many years with proper care. A key to keeping dahlias from season to season is to overwinter the plants.

Dahlias are native to the warm climates of Central America and Mexico, but in colder climates, gardeners can overwinter these plants in a few different ways. The method you choose depends on the conditions in your garden, the weather, and the resources at your disposal.

1. 1. Keep the dahlias in your garden. If you live in USDA hardiness zone eight or higher, you can keep dahlias in the ground over winter. In frost-free climates, they will bloom year-round. If the temperature goes below freezing on some nights, they will lose their foliage and go dormant, but they will return to vibrant, blooming life the following spring. If the ground freezes, however, this will kill the plants.
2. 2. Bring potted dahlias indoors. If you’ve got your dahlias already potted, overwintering them can be a simple matter of bringing them inside at the end of the growing season. To do this, wait until after the first frost. This coldness will cause the plants to go into dormancy. Then, cut them back to about soil level. Before winter arrives in full, move them inside to a cool, dry, darkened place—a basement or garage works, so long as the tubers don’t freeze.
3. 3. Dig up the dahlia tubers. In the colder zones, the most popular method for storing dahlias through the winter is to dig up dahlia tubers and store them inside. You’ll want to wait until after the first frost has prompted the dormancy of the plant. Cut them back to a few inches above the soil, and after ten days or so, gently dig up the tubers with a garden fork or a spade, digging at least a foot away from the stem to avoid damaging the fragile tubers. After digging the tubers, lift them out of the soil, gently brushing away the excess dirt. Clean and trim the largest, healthiest looking tubers; these are the ones you’ll be overwintering. Hang them upside-down with twine, out of direct light, for a few weeks to cure. Then, transfer the tubers to a cardboard box lined with newspaper or a brown paper bag. Pack lightly with peat moss lightly sprayed with water—you want a slight amount of moisture—and keep in a cool, dark, primarily dry place for the winter.

After the cold winter passes, it’s time to replant your dahlias. Wait until spring or early summer; you want the last frost to be long over. Give the tubers a short soak in warm water or compost tea before replanting them. Ideally, the soil temperature should be about sixty degrees Fahrenheit.

When overwintering dahlias, keep the following tips in mind:

1. 1. Cut the dahlias back. If your dahlias go dormant from the hard frost, wait a couple of weeks and then cut the stems down to about six inches high. This gives the tubers a chance to accumulate the necessary sugars for keeping the plant alive through its winter months. Covering the dormant, cut-back dahlias is a further way to keep them safe through the winter to next year. A nice layer of mulch will help insulate the soil, and the bulbs, from the coldest weather.
2. 2. Prevent fungus. Use a fungicide, such as powdered sulfur, to prevent root rot while the tubers are overwintering. You can administer a light dusting using a zip-top bag. Add the tubers to the bag, moving them around to get a slight, even covering. Be sure to use protection such as gloves and a mask if you use this method.
3. 3. Add storage medium. You can use other mediums besides peat moss to preserven dahlia tubers, such as sawdust or vermiculite. Experiment with different options to see which one works best for you and your flowers.
4. 4. Discard the mother tuber. The mother tuber is the tuber from which the last year of growth has arisen. It will be more wrinkled and darker than the others and located centrally in the cluster of tubers. Because this tuber has so directly supported the plant, it has a much lower chance of surviving the winter and should be discarded.
5. 5. Check on the tubers. During the winter, it’s good to periodically check on your dahlia tubers to make sure they haven’t dried out. If they look shriveled, giving them a spritz of water will ensure they don’t dry out completely.

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