For dahlia lovers gardening below USDA Zone 8, digging up and storing your dahlia tubers in the fall is an annual ritual. Properly doing so ensures you can enjoy these stunning flowers year after year.
Removing dahlia tubers at the right time is just as important as knowing the proper technique for winter storage.
Below, we teach you how to dig up and store your dahlia tubers to ensure they'll bloom again come springtime.
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When Should You Dig Up Dahlias?
Gardeners typically dig up and store the roots of dahlias (the tubers) in late fall, store them all winter, and replant them in the next spring. Dahlias are prized flowers worth digging up if they don’t typically survive the winter in your area.
As subtropical plants native to Central America, dahlias are sensitive to frost and are only winter hardy in USDA Zones 8 to 11, that’s why they are grown as annuals in cooler climates.
How to Dig Up Dahlias
- Wait until the first frost before digging up the tubers. Mark the first frost date on your calendar and dig up the tubers 10 to 14 days after. During this period, the dahlia tubers develop eyes (like potatoes) that become the next year’s plants—don't skip this important waiting period.
- Cut the dahlia stalks to 4 to 6 inches after the first fall frost when the foliage has turned black. Wait for 10 to 14 days.
- Loosen the soil around the plants with a garden fork or shovel, about a foot from the main stalk.
- Lift each plant out of the ground by grabbing the stem with one hand and placing the other hand below the clump of tubers.
How to Get Tubers Ready for Storage
Clean and Prune the Tubers
Wash the tubers with a garden hose to remove as much soil as possible. Using sterilized pruning tools, remove all the stems and rotten or damaged tubers. Also, remove the mother tuber in the center of the clump which stands out by its crinkly surface and darker color. This original tuber has no energy left to resprout.
Divide the Clumps
This step can be done in the fall before you store the tubers or in the spring. If you don’t see eyes on the tubers (sometimes they only develop during the winter), it’s better to wait until the spring.
If the crow, located at the base of the stem, contains the eyes, cut it into divisions so that each has at least one or two eyes. If you have different dahlia varieties, label each division with the name. Wash the divisions to remove dirt stuck inside the clump.
Tip
Treat the tubers against fungus during the overwintering process by sprinkling the cut ends with sulfur dust (a fungicide) before storing.
Cure the Tubers
Air-dry small tuber divisions out of direct sunlight for at least 24 hours and larger divisions for at least 24 to 36 hours. The time it takes for the tubers to dry depends on the temperature and humidity. Never place tubers on cement to dry because they could become shriveled.
How to Store Tubers for Winter
Store the dahlia tubers where the temperature is above freezing but below 50°F. Use a container that lets air in but retains the moisture of the storage medium (peat moss, vermiculite, wood chips, etc.) so the tubers don’t dry out.
One common way to store tubers is in a cardboard box lined with newspaper and filled with lightly moistened peat moss. Place the tubers flat on the peat moss without them touching each other. Cover themwith an additional inch of peat moss. Store the box in a dark place like a basement, garage, or root cellar.
Check your tubers regularly during the winter and lightly spray them with water if they seem dry. Remove rotted tubers promptly before they infect the rest.
When Should You Plant Tubers in Spring?
Dahlias need warm temperatures to grow. Plant dahlia tubersoutdoors after the last spring frost and once the soil has warmed to a temperature between 60°F and 75°F. Dahlias are similar to tomatoes so you can plant them when you set out tomato plants.
If your growing season is short, or to get a head start on the growing season, plant your dahlia tubers in pots indoors under grow lights a month earlier. Then transplant the tubers outdoors after the danger of a spring frost has passed.