Dig dahlias after the first frost blackens the leaves and before the ground freezes. Cut the stems to 4–6 inches, lift the clump with a fork from about a foot away, clean it and let it dry for a day or two out of the sun. Then pack the tubers in coarse vermiculite, wood shavings or coir, in a container that isn’t airtight, and keep them dark at about 40 °F. Every source we checked puts storage between 34 and 50 °F, and all of them include 40. Check them once a month until spring.
When to dig: after the first frost, before the freeze
There is no rush before frost. The tubers keep maturing while the plant grows, and the American Dahlia Society says mature tubers keep best over winter, so small growers should let them grow as long as practical. Dahlias keep growing after light frosts, and the hard freeze usually comes a few weeks after the first light one.
- Give them time in the ground. A Penn State Master Gardener in zone 5b waits for the first frost, usually in the second or third week of October there, and notes that dahlias need at least 120 days in the ground to make tubers mature enough to store.
- Dig within a few days of a killing frost. Once frost has killed the leaves, Wisconsin Extension digs within a few days so rot can’t get in through the dead tops.
- Beat the frozen ground. Dahlias can take rain but rot if the ground freezes (Oregon State). Where the soil freezes 4 to 6 inches deep, UC Master Gardeners dig by about November 15 or after the first killing frost.
The finder above gives your average first frost and first hard freeze from the nearest NOAA weather station. For the full picture, including the odds of an early frost, see your frost dates by ZIP code.
Do you have to dig them at all?
That depends on your winter. Illinois Extension calls dahlias hardy only to zone 7. Oregon State says gardeners in zone 7 or warmer can leave them in the ground over winter, which saves storage space:
- Pick a bed that drains well, with no standing water.
- Cut the stems to ground level after the first frost.
- Cover the bed with a sheet of 6-mil black plastic, then at least 4 inches of mulch or leaves. The mulch calculator works out how many bags.
- Uncover in spring when there is no more threat of frost, and dig and divide the clumps every three years.
In zone 6 and colder, dig. A Penn State Master Gardener has seen a few tubers survive near a warm house wall, but heavy freezing and winter rain promote rot, especially in zones 6 and lower. Not sure of your zone? Look it up by ZIP code. Voles and gophers also eat tubers left in the ground (Oregon State), which is one more reason some gardeners in warm zones dig anyway.
How to dig and clean the clumps
- Label every plant before frost. The flowers are gone once you dig, and the ADS stresses having the right name on each stake.
- Cut the stalks. Leave 4 to 6 inches of stem as a handle (Oregon State). If no freeze is forecast, Oregon State cuts the stalks and waits 3 to 7 days before digging, which brings the eyes out and makes dividing easier.
- Dig wide. The roots are shallow and spread out (Illinois), so start about a foot from the stem on all sides; Oregon State goes out 18 inches. A digging fork is less likely than a shovel to cut a tuber (Wisconsin).
- Lift gently and drain the stem. The necks break easily, especially right after digging. The ADS turns the clump upside down to drain water from the hollow stem.
- Clean off the soil. Wisconsin, the ADS and Oregon State wash the clump with a gentle stream from a hose before dividing it. If you’ll store whole clumps and divide in spring, Oregon State and Penn State leave the soil on instead and just let the clump dry.
- Dry it in the shade, off concrete. One to two days is the common advice (Oregon State, UC Master Gardeners, the ADS: about 24 hours for small roots, 24 to 36 for large ones). Concrete pulls water out of the tubers and makes them shrivel, so dry them on a screen, a box or a table.
Divide now, or in spring?
Sources split on this, and both work.
| Divide in fall | Store whole clumps, divide in spring | |
|---|---|---|
| For it | Clumps cut easily; some varieties get so hard by spring you’d need a saw (ADS). Smaller tubers take less space. Most growers do it (Oregon State). | The eyes are easy to see once they sprout (Oregon State). Less spoilage in storage, says Wisconsin Extension. |
| Against it | The eyes are hard to find in fall, so some divisions end up with none. | Whole clumps need more storage space, and the soil left on them must be dry before storing. |
If you divide in fall, every division needs a piece of the old stem (the crown) with at least one eye, a whole neck and a healthy body. Throw out tubers with broken necks (Oregon State, UC Master Gardeners) and trim off the thin feeder roots, which hold moisture and promote rot (Penn State, ADS). Necks thinner than a pencil will probably dry out by spring, the Penn State gardener finds. Cut away any brown or rusty spots inside the crown: the ADS reads them as crown rot.
How to store them: cool, dark, a little moist
The goal is a steady cool temperature above freezing, in a medium that keeps the tubers from drying out without making them wet.
- Where: a spot that stays cold but never freezes, such as an unheated basement, a root cellar or the corner of a garage that doesn’t freeze (Wisconsin). Keep the containers off concrete floors (Penn State).
- Medium: coarse vermiculite is the most common (ADS; fine vermiculite holds too much moisture against the tubers). Wood shavings and coir work too; Oregon State notes shavings can make tubers shrivel, so mist them if they do. Wisconsin and Illinois list peat moss, but experienced growers quoted by the ADS warn that dry peat shrivels tubers and wet peat rots them.
- Container: bags, tubs or boxes, with the tubers in layers of medium and not touching (Wisconsin, UC Master Gardeners). Don’t seal them: Oregon State leaves the bag open, Wisconsin warns against airtight containers, and the Penn State gardener drills holes in a plastic bin and leaves the lid unlatched. Penn State advises against cardboard, newspaper and paper bags, which wick out too much moisture. Growers who do use a cardboard or wood box line it with newspaper at least eight sheets thick and keep the top closed, so the medium stays moist (ADS).
- Label: write the variety on each tuber or on the bag once the tubers are dry (Wisconsin, ADS).
Check them once a month
Look at the tubers every few weeks to once a month (UC Master Gardeners, the ADS, Wisconsin). What you see tells you what to change:
| You see | Do this |
|---|---|
| Shriveled, wrinkled tubers | Mist the medium lightly and repack them (Wisconsin), or move them somewhere more humid (UC Master Gardeners). |
| Condensation in the bag, damp medium | Look for rot, let the bag air out before putting it back (Oregon State), or replace damp shavings (Penn State). |
| Mold on the skin | Brush it off and move the tubers somewhere drier (UC Master Gardeners). |
| A soft, rotting tuber | Throw it out before the rot spreads (ADS), or cut out the bad part of a large tuber (Wisconsin). |
Expect some losses. The ADS says good, mature roots stored any of several ways keep at 90 to 95 percent, while UC Master Gardeners warn that thin-skinned fall-dug tubers can lose 20 percent to rot or drying out.
In spring: wake them up, then plant
In March or April, Oregon State moves stored tubers to a spot at 40 to 50 °F so the eyes start to show; the ADS moves them somewhere dark at room temperature. Plant outside when the soil stays around 60 °F for several days, which is late April to the end of May in Oregon (Oregon State). Your last frost date is a useful guide, and our guide to when to plant dahlias is coming.
Questions people ask
Can I leave dahlia tubers in the ground over winter?
In zone 7 and warmer, yes, in a well-drained bed under plastic and at least 4 inches of mulch (Oregon State). In zone 6 and colder they usually rot or freeze, so dig them.
Do you have to wait for frost to dig dahlias?
No, but it helps. The tubers keep maturing until frost stops the plant, and mature tubers store better (ADS). A Penn State Master Gardener says dahlias need at least 120 days in the ground for that.
What temperature should dahlia tubers be stored at?
About 40 °F. The sources range from 34 to 50 °F; most growers aim for 40 to 45 °F (ADS). Never let them freeze.
Should I wash dahlia tubers before storing them?
If you divide them in fall, yes: Oregon State, Wisconsin and the ADS wash the clumps so the eyes show and soil microbes don’t go into storage. If you store whole clumps to divide in spring, Oregon State leaves the soil on and only dries them.
Why did my dahlia tubers shrivel?
They dried out. That happens in warm or dry storage, in shavings or dry peat, in paper or cardboard, or after drying on concrete. Mist the medium and move them somewhere cooler or more humid.
Can you store dahlia tubers in the garage?
Yes, if that spot stays above freezing. Wisconsin suggests a part of an unheated garage that doesn’t freeze; Penn State keeps the containers off the concrete floor.
Sources
- Oregon State University Extension, Dahlias in Oregon (FS 95, Carla Stables, Julie Moore and Evie Smith; revised 2024): dig after a hard frost kills the stalks; stalks cut to 4–6 in; rot if the ground freezes; cut and wait 3–7 days; dig about 18 in from the stalk; fall division most common; wash, dry, discard broken necks, trim feeder roots; coarse vermiculite, coir or wood shavings (shavings shrivel); don’t close the bag; dark, 34–40 °F; check for condensation; March–April at 40–50 °F; spring division without washing; zone 7 and warmer can overwinter in the ground under 6-mil plastic and at least 4 in of mulch, dug every three years; plant at about 60 °F soil, late April to end of May.
- University of Wisconsin–Madison Extension, Storing Tender “Bulbs” for Winter (Susan Mahr; revised 2026): dig after a light frost, within a few days if frost kills the foliage; digging fork; don’t rub off dahlia skin; wash; store at 35–45 °F and 50% humidity in 2–3 in layers of medium, not touching, not airtight; dahlias best divided in spring; dry several hours; check monthly and mist if shriveled.
- Penn State Extension, Don’t Ditch Those Dahlias: Easy Tips for Winter Storage (Mary Niezelski, Master Gardener, Westmoreland County; 2025): at least 120 days in the ground; digs after frost, mid to late October in zone 5b; rot from freezing and winter rain, especially zones 6 and lower; necks thinner than a pencil dry out; trim roots; store off cement where it can’t freeze, 40–50 °F; vented bins with cedar shavings; no cardboard, newspaper or paper bags.
- University of Illinois Extension, Plant of the Week: Dahlias (2015): hardy to zone 7; dig after the first frost, starting at least a foot from the stem; 3–4 in of stem; cure a few days in shade; store in vermiculite or peat at 35–50 °F; water lightly if shriveled.
- UC Master Gardeners of San Luis Obispo County, Dahlias: Digging, Dividing, and Storing (Carol Moore): dig by November 15 or after the first killing frost where soil freezes 4–6 in; undivided clumps give weak stalks and small blooms, so divide every 2–3 years; body, neck and crown; broken necks aren’t viable; up to 20% storage loss from fall digging; dig about 12 in from the stem; dry 24–48 hours, not on concrete; 40–50 °F at about 70% humidity; layers, not touching; check every few weeks; shriveled or moldy tubers.
- American Dahlia Society, Digging, Dividing, and Storing Tubers: 90–95% success; let roots mature, dahlias grow on after light frosts; dig a foot from the stalk on all sides; drain the stem; wash; fall division easier; crown rot; dry 24–36 hours, never on concrete; coarse vermiculite, warnings on peat; 40–45 °F, above freezing and ideally below 50; inspect monthly; warm, dark spot in early spring.