How to Overwinter Dahlias: Dig, Store and Replant

Learning how to overwinter dahlias comes down to four moves: lift the tubers after the first frost, let them dry, store them somewhere cool and slightly humid, then wake them up in spring. Do that and one set of tubers turns into a growing collection, with free plants and bigger clumps every year, instead of a fresh order every spring. Dahlia tubers are fleshy and full of water, so they cannot survive a hard freeze, and in most climates that means they need a little help getting through winter.

This guide covers whether you need to dig at all, how to lift, divide, dry and pack the tubers, what to do with potted dahlias and how to fix rot and shriveling, with a month-by-month calendar at the end. Experienced growers disagree on a few details, such as peat moss and fall versus spring division, so where opinions differ we explain what the sources say and what we would suggest to a beginner.

Jump to: Do you need to dig? | When to dig | Supplies | How to dig | Dividing | Drying | Storing | Pots | In the ground | Problems | Replanting | Calendar | FAQ

Do You Need to Dig Up Dahlias? Check Your Hardiness Zone First

Dahlia tubers are storage organs, packed with water and starch to fuel next year’s growth. When the soil freezes, that water turns to ice and the damaged tissue rots. Whether your tubers survive winter outdoors therefore depends on how cold your soil gets and how wet it stays. Your USDA hardiness zone is a good starting point, but drainage and microclimate matter almost as much as the number on the map.

Zones 3 to 6: dig and store

If your winters bring a hard, lasting freeze, digging is not optional. Even a thick layer of mulch cannot keep soil above freezing through weeks of deep cold, and a frozen tuber turns to mush as soon as it thaws. In these zones, plan to lift every tuber you want to see again next summer and keep it somewhere cool, dark and frost-free until spring.

Zone 7: the gamble

Zone 7 sits on the edge. In a mild winter, tubers in well-drained soil under a deep blanket of mulch often come through fine. In a hard winter, or in heavy clay that stays wet, many do not. If a variety is rare, expensive or sentimental, dig it. If you have plenty of a cheap, vigorous variety, leaving a few clumps in the ground is a reasonable experiment.

Zones 8 and warmer: leave them in the ground (usually)

In mild climates dahlias behave like perennials, but even there the conditions have to be right. Oregon State University Extension says that overwintering in the ground is feasible only in zone 7 or warmer, in a spot that drains well and has no standing water, under at least 4 inches of organic mulch. The Royal Horticultural Society calls leaving tubers in the ground the easiest option but a risk, because an unexpectedly harsh or very wet winter can cause losses, and it suggests lifting them if your soil is heavy. Washington State University Extension Master Gardeners in the Pacific Northwest, where winters are mild but wet, describe a mix of approaches: digging and storing is the conventional advice, but one gardener switched to leaving her tubers in the ground after struggling with mold in storage.

When to Dig Dahlia Tubers

The signal to start is frost. Once the first fall frost leaves the foliage blackened and limp, the plant has finished for the year and the tubers can come out. Until then, leave the plant alone. The leaves keep feeding the tubers, and the roots continue to mature late into the season.

The American Dahlia Society (ADS) adds a useful refinement: tubers that stay in the ground longer are more fully developed and keep better over winter. Many regions get a light frost that ruins the flowers and the top growth, followed by a hard freeze a few weeks later, and the roots keep maturing in between. For a home gardener with a modest number of plants, waiting a week or two after the foliage blackens, as long as the soil is not freezing solid, is a sensible compromise.

There are exceptions to the waiting rule:

• A deep freeze is forecast. If the ground is about to freeze solid, dig right away rather than risk the tubers.
• Weeks of heavy rain are coming. Tubers sitting in saturated soil can start to rot, so lift them during a dry spell.
• Your climate has no killing frost. Wait until the foliage yellows and dies back naturally, usually in late fall or early winter.

Resist the urge to cut the plants down early because they look messy. A dahlia that is still green is still working for next year’s tubers.

What You Need Before You Start

Gather your supplies before the first frost, so you are not hunting for a knife with a freezing forecast looming. Most of this is already in a typical garden shed.

• Garden fork or spade: a fork is gentler because it lifts without slicing through tubers.
• Pruners or loppers: for cutting the stalks.
• Sharp knife: a hook-bladed utility knife works well for dividing clumps.
• Bleach solution: one part household bleach to ten parts water, for sterilizing tools.
• Hose or utility sink: for washing off soil.
• Drying surface: newspaper, cardboard or wooden crates (never bare concrete).
• Labels and marker: waterproof tags, plus an indelible pencil or permanent marker.
• Storage containers: cardboard boxes, plastic tubs with lids, or paper and plastic bags.
• Storage medium: coarse vermiculite, wood shavings or slightly damp sand (see the storage section for how they compare).
• Optional: powdered sulfur or another garden fungicide for cut surfaces, gloves and a dust mask.

Safety note: work with sharp tools on a stable surface, wear gloves, and follow the label on any fungicide. Dahlias can cause mild stomach upset or skin irritation in pets, so keep tubers and any treatments where curious dogs and cats cannot reach them.

How to Dig Dahlia Tubers, Step by Step

Step 1: Label and cull

Before you cut anything, walk the garden with a notebook. Make sure every plant has a legible tag with its variety name, because a tuber of unknown variety is much less useful next year. The ADS also recommends discarding weak plants and any that produced poor blooms, so you only save the best stock. If a plant showed signs of virus, such as stunted, mottled or distorted growth, put it in the trash rather than the compost pile. Take a few photos of your favorites in bloom, since you will have forgotten the exact colors by spring.

Step 2: Cut the stalks

Cut each stalk down to about 3 to 4 inches above the soil. Leave enough stem to use as a handle when lifting the clump. Dahlia stems are hollow, and water that runs down them can promote crown rot, so do not cut days ahead of digging unless you cover the open stem with a small piece of foil. Sterilize your pruners in the bleach solution between plants, because virus spreads easily from one dahlia to the next on cutting tools.

Step 3: Loosen the soil all around

Push your garden fork into the ground about a foot away from the stalk on all four sides and rock it gently to loosen the soil. Dahlia tuber necks are brittle, especially right after digging, and a snapped neck can mean a tuber that will not grow or will not store. Always dig wider than you think you need to.

Step 4: Lift the clump

Once the soil is loose on all sides, slide the fork under the clump and lift it slowly. Do not pull on the stalk. The clump comes up surprisingly heavy, a dense knot of fat tubers hanging from a thick crown and wrapped in cold, damp soil. Shake off the largest clods by hand, then turn the clump upside down for a few minutes so any water trapped in the hollow stem can drain out.

Step 5: Let the clump rest for a couple of hours

The ADS suggests that if you dig in the morning and leave the clumps out for a couple of hours, the tubers become noticeably less fragile and are easier to clean without breaking. Keep them in shade or a sheltered spot, away from rain and frost, and keep each tag with its clump at all times.

Step 6: Wash off the soil

Use a hose, or a utility sink in cold weather, to rinse away as much soil as possible. Soil carries microorganisms, so removing it before storage lowers the risk of rot, and a clean clump also makes it far easier to see what you are working with when you divide. Once the soil is gone, healthy tubers show smooth, pale skin and feel firm in your hand. Wash gently. Tubers are brittle, and a hard spray can damage the necks.

Dividing Dahlia Tubers: Fall or Spring?

You have two choices once the clump is clean: divide it now or store it whole and divide in spring. Both work, and both have fans.

The ADS notes that some varieties become so hard over winter that separating them in spring is a real struggle, while it also points out that finding the eyes in fall is harder. Neither choice is wrong. Our own suggestion for a beginner, not an ADS rule, is to store the whole clump and divide in spring, because the swelling eyes show you exactly where to cut.

How to divide a dahlia clump

1. Find the eyes. Eyes are small bumps or pinkish growth points on the crown, which is the thick area where the old stalk meets the tubers. A division without an eye will never grow, no matter how plump the tuber looks.
2. Cut so each piece has a tuber, a piece of crown and an eye. Use a sharp knife and make clean cuts. Tubers do not need to be huge, but they must be mature and firm enough to survive winter without shriveling.
3. Remove every scrap of old stem. Leftover stalk promotes crown rot.
4. Discard the mother root. The ADS says to throw away the old central tuber, because sprouts that rely on it tend to develop fewer feeder roots and weaker plants.
5. Trim thin feeder roots. Fine, hair-like roots hold moisture and encourage rot.
6. Inspect each cut surface. Brown or rusty areas inside the crown or tuber suggest rot. Cut back toward the crown until you reach clean, creamy flesh. If no clean section with the crown remains, discard the tuber.
7. Sterilize your knife between clumps. Dip it in the bleach solution each time, because cutting tools can spread virus from one clump to the next.

Insect holes are only a problem if they open the way to rot. If a hole sits partway down a tuber, cut above it and keep the healthy upper portion.

Drying, Treating and Labeling Your Tubers

Let the tubers dry

After cutting and washing, spread the tubers out in a single layer to dry in a shaded, airy spot indoors. Expect about 24 hours for small roots and 24 to 36 hours for medium to large ones, depending on temperature and humidity. The tubers should feel dry on the surface but still plump. Never dry them on bare concrete, because it draws moisture out of the tubers and makes them shrivel. Use newspaper, cardboard or a wooden crate instead.

Treat the cut ends (optional)

Many home gardeners dust cut surfaces with powdered sulfur or dip the tubers in a fungicide solution before storage. This is optional. The ADS article notes that its author, after decades of growing, found no difference in how well tubers kept with or without a fungicide dip, and that the most important step is cutting away any sign of fungus before packing. If you do use a fungicide, wear gloves, follow the label exactly and keep it away from pets and children.

Label every tuber or clump

Mark each division with its variety name or a code you will not lose. An indelible pencil works well on tubers that are still slightly damp, while a permanent marker works on completely dry ones. If you use a code, write the key in your notebook and take a photo of it. It also helps to mark your best performers with a star so you know which tubers to propagate from next year.

How to Store Dahlia Tubers Over Winter

Good storage comes down to three things: the right temperature, the right moisture and regular checking. Get those right and nearly any method works. The ADS says that any of several storage methods should yield 90 to 95 percent success with good, mature tubers from healthy plants.

Ideal storage conditions

• Temperature: cool, steady and above freezing. Iowa State University Extension recommends 40 to 50 degrees Fahrenheit, the ADS gives 40 to 45 as the ideal, and its guide to dahlias after the first frost advises keeping storage at around 40 to 50 degrees all winter. Freezing ruins tubers, while warmth encourages fungus and premature sprouting.
• Darkness: light is not needed and can trigger sprouting.
• Moisture: tubers need a little humidity around them so they do not dry out, but the medium must never be wet. The container should keep that moisture in, while the medium lets moisture move gently between itself and the tubers.

Choosing a storage medium

Here is how the common options compare, based on the ADS guidance and general grower experience:

Choosing a container

Many container types work, as long as they hold moisture in the medium. Ventilated cardboard boxes, plastic tubs, paper grocery bags and plastic vegetable bags have all been used successfully. A few principles apply to all of them:

• Layer, do not pile. Put a layer of medium in the bottom, add a layer of tubers that do not touch each other, then cover with more medium. Repeat if needed.
• Use plenty of medium. The ADS recommends at least as much medium as tubers by volume.
• Line cardboard boxes. Cardboard lets moisture escape. Line the sides with several sheets of newspaper and keep the top closed.
• Adjust for your climate. In a very dry basement, or with thin, small tubers, close bags more tightly. In a very humid space, poke a few small holes in plastic bags or leave them loosely twisted so a little air can escape.
• Label the outside. Write the varieties inside each box on the lid or bag, so you can find what you need without digging through everything.

Where to store your tubers

You need a place that stays between about 40 and 50 degrees Fahrenheit all winter. Good options include:

• the coldest corner of an unheated or partly heated basement
• a root cellar
• an insulated garage that stays above freezing (some growers add a small space heater only for the coldest nights)
• a closet or unheated room against an exterior wall

Avoid a warm utility room, which can trigger early sprouting, and an uninsulated garage or shed that drops below freezing. One long-time grower quoted by the ADS even uses a discarded refrigerator that is not plugged in, with a jug of ice replaced every few weeks to keep the temperature and humidity steady. A thermometer placed in the storage spot is a cheap way to know what is really happening.

Check your tubers monthly

Set a reminder to open your containers once a month. The ADS recommends removing any tuber that shows signs of rot straight away, so it does not spread to healthy neighbors. When you check:

• Healthy tubers feel firm and plump, a little like fresh potatoes, and smell clean and earthy.
• Slightly wrinkled tubers are probably losing moisture. Add a small amount of moisture to the medium or tighten the container.
• Slimy, mushy or moldy tubers are the ones to remove, and they often smell sour or musty. If only part is affected, cut back to clean tissue, let the cut dry and repack it in fresh medium.
• Early sprouts mean the storage space is too warm. Move the container somewhere cooler.

Overwintering Dahlias in Pots

If your dahlias grew in containers, you have two good options.

Option 1: store the whole pot

After the first frost, cut the stems to a few inches, stop watering and let the soil dry out. Move the pot to a cool, dark, frost-free place, ideally 40 to 50 degrees Fahrenheit. The mix should stay nearly dry, with only a light sprinkle of water if it becomes bone dry, because wet soil in storage invites rot. In spring, bring the pot into the light and begin watering once you see growth.

Option 2: tip the tubers out and store them like garden tubers

Slide the root ball out of the pot, shake off the mix, wash, divide if you like and store the tubers in medium exactly as described above. This saves space and lets you inspect the tubers. For pot-grown roots, the ADS describes washing the clump, removing hair roots, letting it dry for a day or two and bagging it with vermiculite, or alternatively leaving the roots in the pot and wrapping the whole pot in several sheets of newspaper inside a paper bag.

Leaving Dahlias in the Ground: How to Do It Right

In mild, well-drained gardens, leaving tubers where they are can work beautifully and saves a lot of work. If you want to try it, do it carefully.

1. Check drainage. Tubers sitting in soggy soil usually rot. Raised beds and sloped sites are safer than low, heavy clay.
2. Cut stems and mark the spot. After frost, cut the stalks to a few inches and push in a stake or tag so you do not forget where the clump is, or dig into it by accident.
3. Mulch deeply. Cover the area with 4 to 6 inches of loose, dry insulation such as straw, shredded leaves or bark. In very wet climates, some gardeners also cover the mulch with a board or sheet of plastic to shed rain, as long as air can still circulate.
4. Pull the mulch back gradually in spring. Remove it as the soil warms, so the sprouts are not smothered, and keep an eye on the forecast for late frosts.
5. Protect new shoots from slugs. WSU Extension Master Gardeners warn that tender new dahlia growth is irresistible to slugs, so set out slug control as shoots emerge.

Be realistic about the trade-offs. In-ground tubers cannot be inspected, a harsh winter can wipe them out, and rodents may help themselves. Over time, clumps also become crowded and perform worse, so plan to dig and divide them every few years. A good compromise in borderline climates is to dig the varieties you care most about and leave the rest.

Common Problems and How to Fix Them

Tubers are rotting or moldy

The usual causes are medium that is too wet, tubers that were damaged or not fully dry when packed, a piece of stem left on the crown, or storage that is too warm. Remove affected tubers right away, cut any salvageable ones back to clean flesh, let the cut dry for a day and repack in drier medium with space between the tubers.

Tubers are shriveled

Shriveling means moisture is escaping, either because the container is open, the medium is too dry, or the room is too warm and dry. Tighten the container, add a small amount of moisture to the medium, and move it somewhere cooler. Tubers that are wrinkled but still firm often recover once planted in spring.

Tubers are sprouting too early

Sprouting in midwinter means the space is too warm. Move the tubers somewhere cooler. If the sprouts are already long, pot the tubers up and grow them on in a bright, cool spot rather than letting the shoots grow weak in the dark.

Mice or rodents are eating the tubers

Mice treat dahlia tubers as a winter snack. Store tubers in containers with tight lids, in metal or thick plastic bins, rather than in open boxes on a garage floor.

Labels are lost or faded

Write the variety name directly on the tubers and on a tag inside the container, and photograph the labeled containers. A tuber with no name still grows, but you lose the ability to plan your garden.

You cannot find any eyes when dividing

Do not panic. Keep the clump whole until spring, when the eyes swell and become easy to see. The ADS also notes that if you simply cut, some divisions will have eyes.

Tubers froze in storage

Frozen tubers turn soft, dark and watery once they thaw. They will not recover, so discard them and move the rest to a spot that stays above freezing.

Waking Up and Replanting Dahlia Tubers in Spring

Step 1: Wake the tubers

In late winter or early spring, move your tubers to a warmer place at room temperature, still dark, to encourage the eyes to swell. The ADS suggests adding about a teaspoon of water per quart of bag space a week to ten days before you take the tubers out, retying the bag, and keeping it warm. This is also the time to divide stored clumps, because the eyes are now easy to find as small pink bumps.

Step 2: Start tubers in pots (optional but worthwhile)

Starting tubers in pots indoors about 4 to 6 weeks before your last frost date gives you a bigger plant and earlier flowers, which is especially valuable in cold climates with short seasons.

• Use a 1-gallon pot with drainage holes and fresh, well-draining potting mix, not heavy garden soil.
• Lay the tuber horizontally with the eye facing up and cover it with about an inch of damp mix.
• Water lightly once, then wait. Tubers need very little water until shoots appear.
• Move the pot to a bright, cool spot as soon as green shoots show.
• When you have several sets of leaves, you can take cuttings from the strongest shoots to make extra plants.

Step 3: Harden off

About a week to ten days before planting out, start putting the pots in a sheltered, shady spot outdoors for an hour or two, then gradually lengthen their time outside and introduce more sun.

Step 4: Plant outdoors at the right time

• Timing: plant when the soil has warmed to about 60 degrees Fahrenheit, typically one to two weeks after your last average frost date. If it is safe to plant tomatoes outside, it is safe to plant dahlias.
• Site: choose a spot with at least six to eight hours of direct sun and well-drained soil.
• Depth: plant dormant tubers about 4 to 6 inches deep, lying flat with the eye facing up. Set potted plants at the same depth they grew in the pot.
• Spacing: allow roughly 18 to 24 inches between large varieties and 12 to 18 inches for smaller ones.
• Stakes: push in the stake before or at planting, so you do not spear a tuber later.
• Water: water lightly at planting and then only sparingly until shoots appear. Soggy, cold soil is the fastest route to rot.
• Slugs: guard new shoots, which are a favorite slug snack.

Month-by-Month Dahlia Storage Calendar

These timings are for the Northern Hemisphere. In the Southern Hemisphere, shift everything by about six months.

Quick Checklist: How to Overwinter Dahlias

1. Wait for frost to blacken the foliage.
2. Label plants and discard weak or diseased ones.
3. Cut stalks to 3 to 4 inches and sterilize tools between plants.
4. Dig a foot away from the stalk on all sides and lift gently.
5. Let clumps rest for a couple of hours, then wash.
6. Divide now or store whole and divide in spring.
7. Dry tubers for 24 to 36 hours, away from concrete.
8. Pack in coarse vermiculite or wood shavings, in layers.
9. Store at 40 to 50 degrees Fahrenheit and check monthly.
10. Wake, divide, pot up and plant out in spring.

Frequently Asked Questions About Overwintering Dahlias

How do you store dahlias over winter?

Dig the tubers after the first frost, wash and divide them if you wish, let them dry for 24 to 36 hours, then pack them in layers of coarse vermiculite or wood shavings in a ventilated box, bag or lidded tub. Keep them in a cool, dark place at 40 to 50 degrees Fahrenheit and check them monthly for rot or shriveling.

Can you leave dahlia tubers in the ground over winter?

In zones 8 and warmer, yes, if your soil drains well. In zone 7 it is a gamble that works best with deep mulch and good drainage. In zones 3 to 6, the ground freezes too deeply, so you need to dig and store the tubers. Even in mild areas, wet soil can rot tubers, so drainage matters more than the zone number.

What temperature is best for storing dahlia tubers?

Aim for 40 to 50 degrees Fahrenheit, and ideally 40 to 45. Below freezing damages tubers, while warm storage encourages rot and early sprouting. A basement, root cellar or insulated garage that stays above freezing usually works.

Is peat moss good for storing dahlia tubers?

Opinions differ. Many retail and garden guides recommend peat moss, but the American Dahlia Society cautions that dry peat can shrivel tubers while moist peat can promote rot. Coarse vermiculite or dust-free wood shavings are safer choices for most gardeners.

Why did my stored dahlia tubers shrivel or rot?

Shriveling usually means the storage medium was too dry or the container let moisture escape. Rot usually means the medium was too wet, the tubers were damaged or not fully dried, a piece of stem was left on, or the room was too warm. Fix the conditions, remove bad tubers early and give the survivors more space.

Can I overwinter dahlias in pots?

Yes. Cut the stems back, let the soil dry out, and move the pots to a cool, dark, frost-free place at 40 to 50 degrees Fahrenheit. Keep the mix nearly dry through winter, then bring the pots into the light and resume watering in spring when shoots appear. Alternatively, tip the tubers out and store them like garden-grown tubers.

The Bottom Line

Overwintering dahlias is a few hours of work in fall and a monthly check-in over winter, and it pays you back with free plants, bigger clumps and the satisfaction of growing your own collection. If you are new to it, keep things simple: wait for frost, dig gently, store whole clumps in coarse vermiculite or wood shavings at 40 to 50 degrees Fahrenheit, and divide in spring when the eyes are easy to see. Keep your labels clear, check the tubers regularly, and do not be discouraged by a few losses in your first year. Each season you will learn more about what works in your own garden and climate. And while the fall garden is open, see what flowers to plant in fall for spring blooms to fill the space your dahlias leave behind.

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