How to Dig, Divide and Store Dahlia Tubers: An Australian Grower's Guide

If there's one gardening job that seems to make even experienced gardeners nervous, it's digging and dividing dahlias. Every autumn my inbox starts filling with the same worried questions. When should I dig them? How do I know they're ready? What if I snap the neck? Do I really have to store them at all?

I understand the nerves completely. Spend five minutes searching online and you'll find dozens of different methods, each claiming to be the right one, and most of them written for freezing Northern-Hemisphere winters that look nothing like ours. Before long it's easy to believe that one wrong cut, or the wrong storage method, will cost you next summer's flowers.

The good news is that dahlias are far more forgiving than the internet would have you believe. After growing thousands of dahlias here at Petal & Bee Flower Farm on the NSW South Coast, I've learnt that success isn't about following a perfect set of rules. It's about reading your own garden, paying attention to your plants and finding a method that works consistently in your conditions.

I've certainly learnt that the hard way. Some years I've dug earlier than planned because of relentless rain. I've accidentally sliced through tubers while lifting a clump. I've changed my storage approach more than once, and one winter, when my shed wasn't ready in time, I ended up storing hundreds of clumps under a hedge and hoping for the best. (More on how that turned out later.) Through all of it, one thing has become very clear: there isn't one perfect way to dig, divide and store dahlias. There are simply methods that suit different climates, different gardens and different growers.

So in this guide I'll walk you through how I actually do it here on the farm, step by step, and share a few of the lessons that have saved me the most heartache. Whether you're lifting your very first clump or you've been growing dahlias for years, my hope is that you'll come away feeling far more confident about tackling the job yourself.

Do You Even Need to Dig Your Dahlias?

Possibly not, and this surprises people. In much of Australia you don't have to lift your dahlias every single year.

The rule that you must dig comes from climates where the ground freezes solid for weeks and any tuber left in the soil turns to mush. Our winters are a different story. Down here, frost rarely troubles a dormant tuber sitting quietly in the ground. Our real enemy is water. Cold, waterlogged soil causes rot long before frost could do any damage.

So if your soil drains freely and doesn't sit soggy through winter, your dahlias can often stay happily in the ground until you're ready to divide closer to spring. That's exactly what I do with many of mine. You'd still want to lift and divide every few years to stop clumps becoming overcrowded and flowering poorly, and you'd dig sooner if your soil stays wet, if you're moving plants to a new bed, or if you simply prefer storing tubers somewhere you can keep an eye on them. There's no single right answer, only the one that fits your garden.

When to Dig

Forget the calendar and watch the plant instead. As a rough guide, dahlias need around 90 to 120 days in the ground to build a good set of tubers. You can wait until frost blackens the foliage if you like, but you don't have to, a green, actively growing plant digs up perfectly well.

One myth worth putting to rest: dahlias don't "pull their energy down" into the tubers the way spring bulbs do, so there's no need to cut the plant back to force it into dormancy. The tubers are already there, formed while the plant was still growing. Tuber development is driven by shortening days and cooling autumn temperatures, not by what you do with the secateurs. If you're going to make a mistake, err towards patience, because tubers dug too early can be under cured and more likely to rot or shrivel in storage.

Here on the South Coast our winters are mild, so my preference is to leave clumps in the ground for as long as I sensibly can. In a normal year, when the ground stays well-drained, I'll wait until late winter and then lift, divide and replant in one go, straight back into the soil. No storage at all, which is far less work and far less fuss. But if we've had an unusually wet run and I'm worried about rot, I'll lift earlier than usual and store the clumps whole instead, then come back and divide them later once things settle down. Same job either way, just split across a longer window when the weather forces my hand.

When to Lift: A Rough Guide by Region

I garden in a warm temperate, coastal climate, so my "leave them in the ground" approach won't suit everyone. Australia covers an enormous range of conditions, and the single biggest factor isn't really latitude at all, it's drainage. Free-draining soil is what lets tubers safely stay in the ground; cold, wet, waterlogged soil is what forces you to lift them, wherever you happen to live. Use the guide below as a starting point, then adjust for your own patch.

Region / climate	In ground or lift?	When to dig	Notes
Cool temperate & cold (ACT, southern NSW, Southern Highlands, most of Victoria & Tasmania, alpine areas)	Lift & store — only leave in ground if soil drains very freely	Late autumn to early winter	Cold, wet ground rots tubers. Don’t leave them sitting in waterlogged soil over winter.
Warm temperate & coastal (coastal NSW, including the South Coast)	Leave in ground only if soil drains freely; lift mainly to divide	Late winter to early spring	My own zone. I only lift early if a wet spell threatens rot. Free-draining soil is essential.
Subtropical & warm humid (SE Queensland, northern NSW)	Leave in ground only if soil drains very well; otherwise lift to divide	Autumn to winter, in the cooler, drier weather	High rainfall and humidity make rot the main risk, so only leave tubers in the ground where drainage is excellent.

The through-line is simple: if your soil sits wet and cold through winter, lift and store. If it drains freely, you have the luxury of leaving them in and lifting mainly to divide.

How to Dig a Clump (Without Wrecking It)

The digging itself is the easy and satisfying part, and a few simple habits make all the difference between a full crate and a pile of damaged tubers.

Start wide and use a fork. Begin about 30 cm out from the centre of the plant, not right up against the stems, and work your way around the clump in a circle, gently loosening the soil as you go. Once it's loosened all the way round, angle the fork underneath and ease the clump up. You'll often feel and hear a satisfying "pop" as it releases. I much prefer a fork to a spade here, because there's far less chance of slicing tubers, and the soil falls away from the tines more easily. That 30 cm of clearance is what protects the tubers, dig in too close and you'll spear straight through them.

Keep your tools sharp. Clean, sharp cuts heal over; ragged, crushing ones invite rot. This matters at digging and even more so at dividing time.

Sterilise your blades between plants. This is the tip most home gardeners skip, and it's the one I'd never skip myself. Dahlia viruses spread mechanically, meaning they hitch a ride on your blades. Cut into an infected plant, then into a healthy one, and you can carry the virus across without ever seeing it, until the following season when that plant grows up sickly. Keep a jar of disinfectant or rubbing alcohol beside you and wipe your blades between plants, especially between different varieties. And before you lift a single clump, walk the patch and pull out any plant that struggled or showed mottled, streaky, distorted foliage. Bin or burn those, never compost them, and never store their tubers, or you risk contaminating others.

Label as you go, not later. The moment a clump leaves the ground its identity starts to slip away, and it happens faster than you'd think when you're busy and clumps are piling up. What felt unmistakable in the garden becomes an anonymous lump by afternoon tea. A quick loop of flagging tape with the variety name, or a labelled crate if it's all one variety, saves a very frustrating spring.

And if you do nick a tuber while digging, don't panic, it happens to all of us. As long as the neck stays intact, it can still grow. Just let the fresh cut dry and callus over before it goes into storage.

How to Divide a Clump

Dividing is the part people dread most, and the part that clicks fastest once you actually start. Every clump you lift will be different. Some come apart like a tidy bunch of bananas; others are a dense, tangled knot that looks impossible. Both are completely normal. The trick is to slow down, work one tuber at a time, and accept from the outset that you'll lose a few. Everyone does.

Before you keep anything, you need to know what makes a tuber worth keeping. A tuber will only grow next season if it has three things:

●      A crown with an eye — the eye is the growing point, the little bud the new plant sprouts from. No eye, no plant.

●      An intact neck — the narrow bridge joining the tuber body to the crown. This is the part people lose most.

●      A healthy body — the plump storage organ that fuels that first burst of spring growth.

The neck deserves special care because it snaps so easily, and a tuber with a broken neck can look and feel perfectly firm yet never grow. That's why you should always lift and handle clumps from underneath rather than tugging on individual tubers.

Here's the order I work in:

1.  Clean the clump up first. Knock off excess soil, trim away straggly roots and remove any obviously rotten, broken or shrivelled tubers. Clearing the clutter makes it far easier to see what you're working with.

2.  Start with the easy tubers. Pick off the obvious, well-placed ones around the outside and work gradually inward. There's no correct place to begin, and each tuber you remove opens up your view of the rest.

3.  Be bold with big, tangled clumps. This is where beginners freeze. Don't tiptoe around a knot you're scared of. Take your loppers, or even a hammer and a sharp chisel, and split the whole thing down the middle. Assess what you've exposed, then quarter it if you need to. Yes, you'll sacrifice a couple of tubers making that cut, but a clear view is worth far more than the pieces you lose, and you'll almost always have plenty of strong tubers left.

4.  Hunt for the hidden eyes. Cutting a clump open nearly always reveals eyes you couldn't see from the outside, tucked underneath and deep in the crown. This is the payoff for splitting boldly.

Two things that will save you tubers. First, don't be put off by looks, some of the ugliest, most misshapen tubers I've ever kept have grown into spectacular plants.

Second, if you genuinely can't find an eye, keep the tuber anyway. Eyes often shrink during curing and swell again in spring, and I've kept plenty of tubers I was unsure about only to be delighted when they sprouted. A tuber you keep costs you nothing but a little space; one you throw out is gone for good. When in doubt, keep it.

And don't skip the cinnamon. This is one of my favourite tricks, and it lives in most kitchen cupboards. Once you've divided, let the cut ends dry for a few hours, then dust them lightly with ordinary ground cinnamon before packing them away. Cinnamon acts as a gentle, natural fungicide, helping to dry the cuts and hold rot at bay, without reaching for any chemicals. It's cheap, easy and genuinely effective.

How to Store Your Tubers Over Winter

The goal of storage is balance, what I think of as the Goldilocks zone. You want your tubers cool enough that they don't sprout early and waste their energy, above freezing so they aren't damaged, moist enough that they don't shrivel, and dry enough that they don't rot.

Getting all four to sit in harmony is the whole art of it. If you're ever forced to choose, lean slightly dry rather than wet, a shrivelled tuber can often be plumped back up, but rot spreads fast and takes its neighbours with it.

Storage mediums help buffer that balance around the tubers. The common ones each behave a little differently:

●      Coco coir — affordable, holds moisture well, and can be tipped into the garden afterwards. A favourite of mine.

●      Vermiculite — sterile and moisture-retaining, though pricier and can run dry over time.

●      Potting mix — cheap and available everywhere; I often use a cheap mix with perlite stirred through it.

●      Rice hulls or wood shavings — light, clean and good for airflow; hulls tend to run slightly drier.

●      Sawdust or plain paper — cheap; sawdust is drying and messy, while paper is handy for wrapping tubers individually to isolate them.

Whatever medium you choose, pack the tubers into crates or tubs that let a little air move through, keep them up off any bare concrete floor (which quietly wicks the moisture straight out of them), and protect them from rats and mice, who adore stored dahlias and can wipe out a serious chunk of your collection over one winter. 

Then, most importantly, check on them every couple of weeks. This one habit separates good storage from disappointing storage. Surface mould on a still-firm tuber usually wipes off and can be dusted with cinnamon; rot needs cutting out straight away before it spreads. A tuber caught early in week three can almost always be saved, while the same tuber ignored for a month often can't. Ten minutes every fortnight is all it takes.

What actually works for me

To be clear, in a normal year I don't store at all. I leave the tubers in the ground until late winter, then lift, divide and replant on the same day, and the soil does the storing for me. The advice below is for the years I'm forced to lift early.

When heavy rain has me worried about rot and I lift ahead of schedule, here's what I do. I try to keep as much soil clinging to the clumps as possible, because that layer of soil insulates and protects the tubers. I store the clumps whole and upside down so any moisture drains away from the crown rather than pooling in it and causing rot, and I hold off dividing until I'm ready to replant.

Through winter, I check every few weeks, give a light misting if a clump looks dry, and pack any clump that's lost a lot of its soil into a storage medium to make up for the lost protection.

And that hedge I mentioned at the start? One year the shed simply wasn't ready in time, so I stored whole clumps outside under a hedge, half-expecting to lose the lot. The chooks dirt bathed amongst them too. I ended up leaving them there the entire season and suffered barely any loss at all. It's my favourite proof that dahlias are far tougher than we give them credit for, and that the best method is always the one that works for your space, your climate and your situation. Don't be afraid to experiment.

Troubleshooting: Common Problems

Even in a good year you'll strike the odd problem. Here's how to read the most common ones at a glance and what to do about each.

What you’re seeing	Likely cause	What to do
Soft, wet or collapsing tuber (rot)	Too wet or too warm in storage, or damage during digging	Cut back to firm, clean tissue. If the crown or neck has rotted, discard it. Replace any contaminated medium.
Shrivelled, wrinkled, very light	Too dry or too warm; long, skinny tubers dry out fastest	Lightly mist the medium. Slightly wrinkled usually plumps back up; fully dried out is gone.
Surface mould, tuber still firm	High humidity and poor airflow	Wipe it off, dust with cinnamon, and improve airflow. Usually perfectly fine.
Can’t find an eye (a “blind” tuber)	Eyes shrink when dormant and are easy to miss	Keep it. Store the whole clump and re-check in late winter as the eyes swell.
Snapped neck	Rough handling, or pulling on individual tubers	Not viable, discard it.
Sprouting early in storage	The storage spot is too warm	Move it somewhere cooler. If it’s already late winter, it’s nearly time to divide and plant anyway.

The golden rule runs through all of it: check often, act early, and when a tuber is only partly affected, cut back to clean, firm tissue rather than throwing the whole thing away.

Frequently Asked Questions

Do I have to dig up my dahlias every year?

Usually not, if you have mild winters and free-draining soil like much of coastal Australia. Leave them in and lift to divide every few years. Dig sooner if your soil stays wet over winter.

Will frost kill tubers left in the ground?

A light frost won't harm a dormant tuber. Prolonged deep freezing will, but that's rare here. For us, cold wet soil and rot are the bigger risk.

Do I need to cut the plant back before digging?

No. Cutting back doesn't drive energy into the tubers, that's a myth. It can make handling easier, but it also creates cuts that spread virus and hollow stems that let water into the crown.

Should I wash my tubers?

Your choice. Leaving the soil on insulates them and saves time, which is what I do. If you wash, use a gentle spray, do it close to dividing time, and let them dry properly afterwards without leaving them exposed long enough to shrivel.

How do I know if a tuber is worth keeping?

It needs a crown with an eye, an intact neck and a firm, healthy body. If all three are there it's viable, no matter how ugly it looks. When you can't tell, keep it, space is cheap and spring is full of surprises.

A stored tuber has gone soft or mouldy — is it ruined?

Not necessarily. Surface mould on a firm tuber usually brushes off; dust it with cinnamon. Soft isn't always dead, "old carrot" soft is usually fine, "old banana" soft is gone. Rot on the crown or neck, though, can't be saved.

The Bottom Line

Digging, dividing and storing dahlias sounds far harder than it turns out to be. Do it a couple of times and it starts to feel completely natural, the kind of seasonal rhythm you look forward to rather than dread. There's no single perfect method, only the one that works for your garden, your climate and your space. When in doubt, keep the tuber. Check your storage often. And remember that the ugliest tubers so often grow the most beautiful flowers.

So my best advice is simply to get out there and give it a go. You'll learn more from one afternoon with a fork and a clump than from any amount of reading, mine included.

 

Written by Nerida of Petal & Bee Flower Farm, who grows, digs and divides thousands of dahlias each season on the NSW South Coast