How to Prepare Dahlias for Winter

Updated September 2026 · Garden Advice Guide

To prepare dahlias for winter in zone 7 and colder, wait until the first killing frost blackens the foliage, cut the stalks back to 4 to 6 inches, and dig the tuber clumps about one to two weeks later. Let them dry for a day or two out of the sun, divide them now or wait until spring, and pack them in a lightly damp medium such as wood shavings, vermiculite, or peat moss. Store them at 40 to 50°F and check them once a month until planting time. In zone 8 and warmer, most dahlias can stay in the ground under mulch, as long as the soil drains well.

Dahlia tubers are not bulbs, and they don't store like bulbs. They are swollen roots full of water, which means they can freeze, rot, or shrivel depending on how you handle them. Get the temperature and moisture right, and one clump dug in October becomes three to five plants next spring.

Digging day runs off your first frost. Look up your average first frost date with our free Frost Date Lookup so you know which week to have the fork and storage bins ready.

Updated September 2026

How to Prepare Dahlias for Winter: Dig Them or Leave Them?

Dahlia tubers die when they freeze. Whether you need to dig comes down to one question: does the soil 6 inches down freeze in your winters? Sources disagree on zone 7, and some call dahlias hardy there under heavy mulch. Zone 7 soil does freeze in a cold winter, though, so the safer rule is to dig in zone 7 and colder and leave tubers in the ground only in zone 8 and warmer.

Cold is not the only killer. Wet soil rots dormant tubers even where it never freezes. A dahlia in a low spot in zone 8 clay is at more risk than one in a raised bed in zone 7.

Saving tubers also keeps your varieties. A named dahlia comes back true from its tuber, while seed from the same plant produces something different.

Step 1: Get the Plants Ready in Late Summer

Winter prep starts a few weeks before frost.

• Stop fertilizing by late August. Late nitrogen keeps plants growing soft and delays the tubers maturing.
• Ease off watering as nights cool in September, especially in heavy soil.
• Label every plant now, while it is blooming and you can still tell them apart. Tie a tag to the stake or push a plant label into the soil beside it. Once frost hits, every dahlia looks the same.
• Keep cutting flowers. Picking does not hurt the tubers, and the plant keeps feeding them as long as the leaves stay green.

Step 2: Wait for the First Killing Frost

A light frost that browns the top leaves is not the signal. You want a killing frost, usually 28°F or colder, that turns the whole plant black and limp. That frost tells the plant to go dormant and starts the tubers toughening their skins for storage.

Then wait. Leaving the clump in the ground for one to two more weeks after the killing frost helps the skins set and makes the eyes, the growth buds on the crown, easier to see. The soil above the tubers shields them from the cold that killed the leaves.

Two exceptions:

• If a hard freeze is coming that could freeze the soil itself, such as several nights in the low 20s or colder, dig right away.
• If frost is late and you need the tubers out, cut the plants back and leave them in the ground for about two weeks before digging. That rest gives the skins the same chance to toughen.

Those are averages. Local dates swing by weeks, so check your own frost date rather than going by the table alone.

Step 3: Cut Back the Stalks

Cut each stalk down to 4 to 6 inches above the ground. Leave that stub; it is the handle you'll use to find the clump, and it keeps you from digging blind.

Dahlia stalks are hollow, and water that collects in them can run down into the crown and start rot. Cut at an angle so water runs off, or cap the cut with a square of foil. Once you dig, you'll turn the clump upside down so the stalks drain.

Move the plant label from the stake to the stalk stub, or tie it on with twine, so the name travels with the clump.

Step 4: Dig the Clumps Without Snapping Necks

The weakest part of a dahlia tuber is its neck, the narrow stretch that connects the fat tuber to the crown. The growth eyes sit on the crown, not on the tuber, so a tuber with a broken neck has no way to sprout. It will look fine all winter and do nothing in spring.

1. Dig on a dry day when the soil is moist but not muddy.
2. Push a garden fork straight down in a circle 12 to 18 inches out from the stalk. Large dinnerplate varieties can spread wider.
3. Loosen the soil all the way around before lifting.
4. Lever the clump up from underneath, supporting it with the fork or your hands. Never lift by the stalk.
5. Shake off loose soil gently and set the clump upside down so the stalks drain.

If you nick a tuber, it can still be stored. Let the cut dry and callus before packing it.

Step 5: To Wash or Not to Wash

Growers split on this one, and both approaches work if you follow through.

If you wash, use a gentle stream from the hose, not a jet nozzle, which scars the skin. Some growers then dip tubers briefly in a dilute bleach solution to cut down on fungal problems. If you do, let them dry completely afterward.

If you don't wash, knock off the big clods and let the rest dry in place.

Step 6: Cure Briefly Before Storage

Curing dahlia tubers is short. The goal is a dry skin, not a dry tuber.

Set clumps upside down, or lay divided tubers in a single layer, somewhere frost free and out of sun and wind, around 50 to 60°F. A garage floor covered with newspaper works. Leave washed tubers until the skin feels dry to the touch, usually one to three days. Unwashed clumps need about the same.

Don't overdo it. Tubers left out for weeks in a warm, dry room shrivel and may not recover. That is the opposite of how gladiolus corms are handled, which is why the long, warm cure in our hardy gladiolus guide does not apply to dahlias.

Step 7: Divide Now or in Spring

You can divide a clump in fall right after curing, or store it whole and divide in spring. Each choice has a real trade-off.

Many experienced growers divide in fall for the easy cutting and space savings, then check eyes again in spring. If you are new to it, splitting each clump into a few large sections in fall and finishing the job in spring is a good middle path.

How to divide:

1. Wipe a sharp knife or pruners with rubbing alcohol between clumps so disease doesn't travel.
2. Cut the old central stalk out of the crown, then split the clump in half down the middle.
3. Keep cutting until each division has three parts: a plump tuber, an unbroken neck, and a piece of crown with at least one eye.
4. Throw out tubers with broken necks, rot, or no crown tissue, along with the old mother tuber you planted last spring, which often goes woody or hollow.
5. Let cut surfaces dry and callus for a day before storage.
6. Write the variety name directly on each tuber with a permanent marker or an indelible pencil.

Step 8: Choose a Storage Medium

Tubers need to sit in something that holds a little moisture, lets air move, and keeps them from touching each other so rot can't jump from one to the next.

Containers: Plastic storage bins with the lid set loosely or a few holes drilled in it, cardboard boxes, or paper bags for small batches all work. Layer medium, then tubers not touching, then more medium, and so on. Label the outside of each container with what's inside.

Match the medium to your space. A damp basement needs a drier medium. A dry garage needs one that holds a bit more moisture, or plastic wrap.

Keep containers where dogs can't get into them. Dahlia tubers can cause mild stomach upset in pets that chew on them.

Step 9: Store Tubers at 40 to 50°F

Temperature is the setting that matters most.

Aim for moderate humidity, somewhere around 70 to 90 percent. Too dry and tubers shrivel; too damp and they rot.

Good spots include an unheated basement, a root cellar, a crawlspace, or an attached garage along the house wall. In a garage that dips below freezing, set the bins inside an insulated cooler or against the shared house wall. A small batch of divisions can go in a spare refrigerator. A min-max thermometer set next to the bins tells you whether your spot really stays in range, which is worth knowing before January rather than after.

Step 10: Check Tubers Once a Month

Open the bins two weeks after storing them, then once a month through March. Pull out a few tubers from different layers each time.

A little wrinkling is normal by February. A tuber that feels firm when squeezed, with a healthy neck and a visible eye, is a plantable tuber even if it isn't pretty.

Leaving Dahlias in the Ground in Zone 8 and Warmer

In zones 8 to 10, dahlias can stay in the ground over winter, and many gardeners get bigger, earlier plants that way.

1. Cut back after frost. In zones 9 and 10 where frost may never come, cut back when the foliage declines in late fall.
2. Mulch 3 to 4 inches deep with shredded leaves, straw, or pine needles. Our mulch guide covers which mulches stay loose and which pack down wet.
3. Make sure the bed drains. Standing water in winter kills more in-ground dahlias than cold does. Raised beds are the safest.
4. Turn off irrigation to that bed for the winter.
5. Pull the mulch back in spring once your last frost passes, so the soil warms and shoots can emerge.
6. Watch the new shoots. Slugs and snails hit emerging dahlia shoots hard in mild climates; see how to get rid of slugs. In-ground dahlias also sprout early, when deer are hungriest, and that timing problem is covered in do deer eat dahlias.
7. Dig and divide every three to four years. Crowded clumps send up lots of thin stems with smaller flowers.

Zone 7 gardeners who want to try it should pick a warm spot against a south-facing wall, use a raised bed with sharp drainage, lay down 6 inches of mulch, and still dig their favorite varieties as a backup.

Dahlias in Containers

Potted dahlias have an easier path. After frost blackens the foliage, cut the stalks back, stop watering, and move the whole pot into a garage or basement that holds 40 to 50°F. The soil in the pot acts as the storage medium. Check once a month, and if the soil is dust dry by January, add a small splash of water around the edge of the pot. In spring, tip the tubers out, divide them if needed, and replant in fresh mix. The same unheated garage holds other containers through winter, and our guide on how to keep potted perennials over winter covers the temperature and watering routine for the rest of them.

Cleaning Up the Dahlia Bed

Dahlia foliage often carries powdery mildew by fall, so bag the frosted leaves and stalks rather than adding them to a home compost pile. For the rest of the garden, including which beds to clear and which to leave standing for overwintering insects, our fall garden cleanup guide covers the whole job.

Worked Example: 15 Dahlias in Zone 6

Say you grew 15 dahlias in zone 6, with an average first frost around October 18 and a basement that holds about 48°F all winter.

From 15 plants you end up with more than 50 good tubers, enough to triple the bed or share with friends. The whole winter job takes about seven hours, and most of that is the one afternoon of dividing.

FAQ

When should I dig up dahlias for winter?

One to two weeks after the first killing frost blackens the plants. That short wait helps the tuber skins toughen for storage. If a hard freeze threatens to freeze the soil itself, dig sooner.

Can dahlias stay in the ground over winter?

In zones 8 to 10, usually yes, with 3 to 4 inches of mulch and well-drained soil. In zone 7 and colder, the soil can freeze at tuber depth, so digging is the safer choice. Wet soil can rot tubers in any zone.

What temperature should dahlia tubers be stored at?

Between 40 and 50°F. Freezing temperatures kill them, and above about 55°F they start sprouting early and shrivel faster.

Do I have to divide dahlia tubers every year?

No, but it helps. Divided tubers store in less space and grow into stronger single plants. Whole clumps can be stored and replanted, though they make crowded plants with more, weaker stems.

Why did my stored dahlia tubers rot?

Usually too much moisture: tubers packed while still wet, a storage medium that was too damp, or water trapped in hollow stalks. Storage above 55°F and tubers touching each other both make it worse. Check monthly and cut out soft spots early.

Why are my dahlia tubers shriveled?

The storage spot is too dry or too warm, or the tubers cured for too long. Lightly mist the medium, cover the bin more fully, or wrap divisions in plastic. Mildly wrinkled tubers with intact necks and eyes usually still grow.

Can I store dahlia tubers in the refrigerator?

Yes, for a small number. Pack them in slightly damp peat or vermiculite inside a paper bag or a vented container, and keep the fridge between 40 and 45°F. Check them monthly, since refrigerator air is very dry.