Dahlia Winter Care: Should You Dig Them Up or Leave Them In?
Dahlia Winter Care
Are dahlias perennial? Will frost kill them? Do I really need to dig them up every year? How do I store tubers over winter? Can I just leave them in the ground? When should I replant them? If you’ve ever asked one—or all—of these questions, you’re in good company. Dahlia winter care can feel a bit intimidating at first, but with a little know-how, it’s easy to keep these summer stunners coming back year after year. In this guide, we’ll walk through exactly what your dahlias need to survive the colder months—whether you’re digging them up or letting them ride it out in the soil.
A History of Dahlias
Dahlias are native to Mexico and Central America, where they thrive in warm climates and rich, well-drained soil. Beloved for their dazzling variety of colours, shapes, and sizes, dahlias range from delicate, daisy-like blooms to dinner-plate-sized showstoppers. They’re classified as tender perennials, meaning they grow back year after year in mild climates but need a bit of extra care in regions with frost. In Canberra, they’re typically grown as summer-flowering plants, blooming prolifically from mid to late summer until the first frost cuts them back. While they look like high-maintenance divas, they’re actually hardy, generous plants—as long as their tubers are protected through winter.
To Dig or Not to Dig: Dahlia Winter Care by Climate
Whether or not you need to dig up your dahlias for winter depends on your local climate. Specifically, how cold it gets and how well your soil drains. In cool to cold climates where the ground freezes (typically USDA zones 8 and below, or anywhere that regularly drops below -4°C / 25°F), you’ll need to lift and store your dahlia tubers. Frost will kill the above-ground plant, but if the soil freezes, it can also rot or split the tubers underground.
In milder climates (zones 9–11 or areas with consistently frost-free winters), dahlias can often stay in the ground with a bit of protection. If your winters are damp but not freezing, it’s still a good idea to mulch heavily and make sure the bed drains well, or you risk losing them to rot. Some gardeners even hedge their bets: dig up their favorites and leave the rest in as an experiment.
A Canberra Gardener’s Approach
Here in Canberra, our climate keeps things interesting. Winters can swing from mild and dry to icy and soggy. So when it comes to dahlias, gardeners are divided.
Personally, I’ve never lost a tuber to frost—but up until this year, all of my dahlias were tucked into well-drained, north-facing beds backed by a northern brick wall. It’s a warm little microclimate, and it seems to have kept them cosy enough to survive Canberra winters without any extra help.
This year, though, I decided to dig them up—not because of the cold, but to divide and conquer. I wanted to split the clumps, share some with friends, create better spacing in my beds, and move a few into new garden areas.
If You Choose to Dig Them Up
When Should You Dig Them Up?
Wait for the first hard frost to blacken the foliage, then cut the stems back to about 10–15 cm above the soil line. At this point, the tubers are dormant and the energy has gone back into the root system. You can dig them up immediately, or leave them for a few days to dry out a bit if the weather allows.
How to Dig, Divide and Store Dahlia Tubers
Step by Step
- Gently dig around the base with a garden fork or shovel, being careful not to stab the tubers.
- Lift the whole clump, shake off excess soil, and hose them clean if needed.
- Let them dry in a cool, airy place out of direct sunlight for a day or two.
- Divide them if desired—make sure each division has at least one “eye” (the little bump that will sprout next season).
- Dust with sulphur powder or cinnamon to prevent rot (optional but helpful).
- Store in sawdust, wood shavings, or coco coir in a box or tub somewhere cool, dark, and dry—like a shed or garage. Avoid places that get below freezing.
Check them once a month and remove any that go soft or mouldy.
How to Check if Dahlia Tubers Are Still Viable
Before planting or storing, it’s a good idea to give your tubers a once-over to make sure they’re still in good shape. Start with a gentle squeeze—healthy tubers should feel firm, plump, and slightly heavy for their size, a bit like a potato. If they’re soft, squishy, hollow-feeling, or smell off, they’ve likely rotted and should be composted or binned.
You might also come across some that are slightly wrinkled or a bit lighter than they were at harvest. That’s usually just a sign of mild dehydration and isn’t a dealbreaker. As long as the tuber is still firm and hasn’t gone mushy, it has a good chance of bouncing back once it’s in the ground and watered.
Keep an eye out for mold or mildew, especially if you stored them in a closed container or somewhere damp. A little surface mold can sometimes be wiped away or treated with cinnamon or sulphur powder, but if it’s extensive or the tuber is soft underneath, it’s time to let it go.
And finally—check for eyes! These are the small bumps or nubs (often near the neck of the tuber) that will become next season’s shoots. If you’re dividing or choosing which tubers to keep, make sure each viable one has at least one visible eye.
Replanting Dahlia Tubers in Spring
Once the risk of frost has passed, it’s safe to get your dahlias back in the ground. Don’t rush this step: planting too early can expose your tubers to cold, soggy soil, which increases the risk of rot before they’ve had a chance to sprout.
Choose a sunny spot with well-draining soil, ideally somewhere that gets at least 6 hours of direct sunlight a day. If your soil tends to hold water, consider adding compost or planting in raised beds to improve drainage—dahlias hate wet feet.
Plant the tubers about 10–15 cm deep, with the “eyes” (the small bumps that sprout) facing up and the tuber laid horizontally. Space them around 30–50 cm apart, depending on the variety and how much room you want between plants.
At planting time, there may be no visible growth yet, and that’s perfectly normal. As the soil warms, the eyes will begin to sprout and push up green shoots. Resist the urge to overwater before they sprout—just a light watering to settle the soil is enough at first.
If you’re planting multiples, this is also a great time to label your varieties. Once they all start growing, it’s nearly impossible to tell which bloom is which until much later!
If You Choose To Leave Them In
If you decide to leave your dahlias in the ground over winter, you’re not alone. Many gardeners in Canberra and other cool-climate regions take the gamble, especially if their soil drains well and their beds are in a sheltered, sunny spot.
Start by waiting until the first hard frost blackens the foliage, then cut the stems back to about 10–15 cm above the soil. Once that’s done, mound up a thick layer of mulch or straw—at least 10 cm—over the crown. This insulating layer helps protect the tubers from sudden temperature drops and also keeps the soil from becoming waterlogged during heavy winter rains.
It’s still a bit of a risk. If your soil is heavy or tends to stay wet, there’s a chance the tubers could rot. But if they’re tucked into well-draining beds, close to a warm wall, or in a microclimate that avoids deep frost, your dahlias just might pull through.
How to Tell if They’ve Survived
Come early to mid-spring, start peeling back some of that mulch to check the soil. If you see plump, firm tubers and the beginnings of fresh green shoots or nubs, your dahlias have made it through. Be patient—they often won’t show new growth until the soil really starts to warm up, especially after a cold winter.
If you’re unsure, give the area a gentle dig and feel for the tubers just below the surface. When they feel mushy, hollow, or foul-smelling, they’ve rotted and will need to be replaced. If they feel firm and look intact, they’re likely still viable, even if there’s no visible growth yet.
Some years, everything bounces back beautifully with lush green shoots and early blooms. Other years… not so much. That’s the joy (and heartbreak) of gardening. Sometimes your dahlias need a bit of tough love, and sometimes they reward you with more blooms than ever.
Common Overwintering Mistakes to Avoid
Overwintering dahlias isn’t difficult, but there are a few common missteps that can cost you your tubers. Here’s what to watch out for:
🌡️ Storing tubers somewhere too warm or too cold
Your dahlias want to be Goldilocks: not too hot, not too cold. If you store them somewhere too warm (like inside the house near a heater), they may dry out and shrivel. Too cold—especially below freezing—and they can turn to mush. Aim for a cool, dark, and dry location like an insulated garage, shed, or basement that stays above freezing but below 15°C.
💧 Not letting them dry properly before storage
After digging, your tubers need a little time to dry out. Ideally, 1–3 days in a well-ventilated, shaded area. Storing them while still damp is one of the fastest ways to invite mold or rot. Give them space to breathe before tucking them away.
👀 Forgetting to check stored tubers for rot
Tubers don’t need much attention during winter, but they do appreciate a monthly check-in. A quick glance and squeeze test will help you spot any that are going soft, moldy, or shriveled. Removing compromised tubers early can help save the rest of the batch.
✂️ Dividing without an “eye”
If you’re dividing clumps before storage, make sure each division has at least one “eye”—that little bump that will grow into next season’s plant. No eye, no flower. It’s easy to accidentally toss viable tubers or keep ones that won’t sprout, so take your time when dividing.
🌧️ Leaving tubers in heavy, soggy soil
If your garden has clay-heavy or poorly draining soil, overwintering in-ground is risky. Soggy soil can cause tubers to rot even if temperatures don’t drop too low. Unless your bed is raised or naturally well-draining, it’s safest to lift and store.
The Verdict?
There’s no one-size-fits-all answer. It depends on your garden, your soil, and your appetite for risk. If your soil drains well and you’re okay rolling the dice, you might leave them in. If you’re working with heavier clay or want to expand your collection through division, lifting and storing is your best bet.
Whether you’re team dig-up or team leave-in, overwintering dahlias is one of those small efforts that pays off in spades come summer. It’s a little extra work for a whole lot of bloom.
Dahlia Winter Care FAQs
Yes—but it depends on your setup. If your potted dahlias live outdoors and you’re in a frost-prone area like Canberra, the tubers are still at risk unless you move the pots into a sheltered, frost-free space like a garage or enclosed porch. Pots tend to heat up and cool down more quickly than garden beds, which can stress tubers or increase the risk of rot if they stay wet. To overwinter in pots, cut back the foliage after frost, let the soil dry out slightly, and move them somewhere protected. Alternatively, you can tip the pots out and store the tubers bare or in sawdust, just like you would from a garden bed.
If your tuber feels shriveled but not completely dried to a crisp, there’s still hope. Try soaking it in room-temperature water for a few hours (up to overnight) to help it rehydrate. Then let it air-dry briefly before planting. Some gardeners also plant slightly shriveled tubers directly into moist soil and let nature take over. If there’s still an eye present and the tuber is firm enough not to collapse when pressed, you may be surprised by how well it bounces back.
Absolutely—sugar cane mulch works well as an insulating layer over in-ground dahlias. It’s light, fluffy, and easy to pile up thickly, helping to trap warmth and wick away moisture from the soil surface. Just make sure you layer it generously—10–15 cm is ideal—and consider topping it with straw or a frost cloth if you’re expecting heavy frost. In spring, you can rake it back and reuse it as regular garden mulch.
If you’re not relying on them for a wedding, a show, or your sanity—then yes, go for it. Leaving tubers in the ground can be a fun way to test your microclimate and see what your garden can handle. Many gardeners use this method to learn which spots in their yard stay warmest over winter. Just keep backup tubers stored if it’s a favourite variety you’d be heartbroken to lose. Gardening isn’t just about playing it safe. It’s also about experimenting and learning what thrives under your unique conditions.
🌸 Love dahlias as much as I do?
They’re not just garden showstoppers—they’re edible, too! Head over to my edible flowers guide to learn which blooms are safe to eat (including dahlias!), plus how to grow, harvest, and use them in your kitchen and cake decorating.
Check out my these cakes decorated with dried edible flowers—somehow, their colours pop even more after drying!
Are You a Cool Climate Gardener?
If you’re dealing with frosts, unpredictable springs, or a short growing season, welcome to the club. Cool climate gardening comes with its own set of challenges—but also some beautiful perks (hello, flavour-packed root veg and glorious autumn colour). It just means you’ve got to time things right, choose the right varieties, and get a bit creative with your setups.
Take chillies, for example. They’re a warm-season crop, but with the right tricks, you can absolutely grow them successfully even in Canberra’s chilly climate. I’ve written a full guide on how we do it at home—Growing Chillies in a Cool Climate: How We Do It in Canberra.
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