Dahlias are frost-tender perennials, meaning their underground storage organs, known as tubers, cannot survive freezing temperatures. For gardeners in climates where the ground freezes, “lifting” is an annual necessity. This process involves carefully excavating the tubers from the garden bed to store them indoors over the winter season. This preservation ensures the tubers remain viable and ready to produce vibrant blooms when replanted the following spring.
Determining the Optimal Time for Lifting
The timing for lifting dahlias is governed by environmental signals, primarily the first hard frost. A hard frost kills the plant’s entire above-ground structure, causing the foliage to turn black. This demise signals the end of the growing season, triggering a final transfer of starches and carbohydrates from the stems down into the tubers for storage.
Wait four to fourteen days after the hard frost before beginning excavation. This waiting period allows for a crucial conditioning process. The tuber’s skin (periderm) toughens up and stabilizes its moisture content, forming a protective layer that helps prevent rot and dehydration during storage. Digging immediately risks lifting immature, thin-skinned tubers that are prone to damage and decay.
Pre-Lifting Preparation and Staking
Preparing the plant above ground simplifies the process and aids in tuber conditioning before digging begins. Cut the main stem down, leaving a stalk four to six inches tall above the soil line. This remaining stem serves as a handle during lifting and helps prevent water from traveling down into the hollow crown of the tuber clump.
Label each remaining stub with the variety name using a waterproof marker or tag tied securely to the stem. This is important when growing multiple varieties, as identification is lost once the clump is removed. After cutting the foliage back, some growers temporarily cover the exposed stem to prevent rain from entering the hollow stalk, which can lead to crown rot.
The Technique of Excavating the Tubers
Lifting the tuber clump requires careful attention to avoid severing the delicate roots. The dahlia’s storage tubers radiate outward from the central stem, making them susceptible to damage from a misplaced spade or fork. Begin excavation by inserting a garden fork or spade into the soil at least twelve inches away from the main stem.
Work around the plant, gently loosening the soil in a wide circle to ensure all tubers are outside the digging perimeter. Once the soil is loose, gently rock the fork or spade to lift the entire clump from the earth. The junction where the tuber meets the stem, known as the neck, is particularly brittle and must be handled with care, as a break here renders the tuber unviable for the following season.
Curing and Preparing Tubers for Winter Storage
Immediately after lifting, preparation focuses on cleaning and drying the tubers for dormancy. Gently shake or brush off the bulk of the excess soil. Avoid washing the tubers unless the soil is heavy clay, as a small amount of soil left on the tubers offers a slight protective layer during storage.
The next step is the “curing” phase, where the tubers dry and heal minor abrasions. Place the clumps upside down in a sheltered, cool, and dry location out of direct sunlight for three to seven days. Positioning them upside down allows any remaining moisture trapped in the hollow stem to drain away from the crown, reducing the risk of rot.
During this drying period, inspect the tubers for signs of damage, disease, or softness, and remove affected parts with a clean, sharp blade. The goal is to ensure the tuber skins are firm and leathery before packing them away. Once dry, the clumps are ready to be stored in a medium that maintains a consistent temperature and moderate humidity throughout the cold months.