09/28/2026
A dahlia clump is one of the best deals in the garden. One tuber planted in spring can turn into a whole cluster of fat, sweet-potato-shaped tubers by fall, and each of those can become its own plant. Toss the clump after the first frost and you throw away a lot of free flowers.
The first question is whether you need to dig at all. Dahlias are tender perennials, generally hardy in zones 8 to 11, where tubers can often stay in the ground under a thick layer of mulch. In colder zones the tubers will freeze and rot over winter, so they need to be lifted and stored indoors.
Timing matters. Wait for a frost to blacken the foliage, which signals the plant has gone dormant. Then cut the stems back, but do not cut them as short as many guides suggest. Penn State Extension recommends cutting back to six inches after a killing frost, then waiting four to eight days before digging. The extra stem gives you a handle for lifting the clump and a place to attach a label. Because dahlia stems are hollow, Penn State also suggests covering the cut tops with foil so rain does not run down into the crown and rot the tubers.
When you dig, loosen the soil in a wide circle about a foot from the stem, then lift the clump gently with a fork. The necks connecting each tuber to the crown snap easily, and a tuber without its neck will not grow. Brush off the soil or give it a light rinse, then let the clump dry in a cool, shady spot for a few days.
Dividing is where many gardeners rush. Each division needs three parts: a piece of the crown with at least one eye, a neck, and a tuber. The eye is a small bud near where the stem meets the tuber, and it is what grows into next year's plant. The catch is that eyes are often hard to see in fall, and they swell and become obvious as days lengthen in spring. Penn State Extension says fall or spring division is a matter of personal preference. Dividing in fall makes the tubers softer to cut and easier to pack, but you may cut off an eye without realizing it. Storing the whole clump and dividing in spring, when the eyes are swelling, is the safer choice for beginners. Either way, tubers with necks thinner than a pencil often dry out before spring, so the thick, plump ones are the keepers.
If you do divide in fall, let the cut surfaces dry for a day in a cool, shady, well-ventilated spot before packing. Then store them in a box or crate with slightly damp peat moss, vermiculite, or wood shavings, in a cool, dark place that stays above freezing. Around 45 degrees Fahrenheit is a good target. University of California Master Gardeners note that fall tuber skins may not fully harden, and that it is common to lose about 20 percent of a fall harvest to rot or dehydration in storage. That is why checking your tubers about once a month is worth the effort. Remove any that turn soft or moldy, and mist lightly if they begin to shrivel.
In spring, after the last frost has passed and the soil has warmed, plant your tubers with the eyes facing up. If you stored whole clumps, this is the moment to divide them, and you will see exactly where to cut. One clump becomes several plants, and several plants become armfuls of flowers next summer. 🌸🌱
