Almost time for the BIG DIG!
A practical guide to labeling, digging, dividing and storing dahlia tubers, with a little less panic and significantly more dirt.
Dahlias spend the summer looking like they belong in a very expensive wedding. Then fall arrives, and suddenly you’re protecting a collection of oddly shaped potatoes. Gardening is a glamorous business.
Here in New York’s Capital Region, the end of flowering season means getting ready to lift dahlias and give their tubers a frost-free winter home. A little organization now can save your favorite varieties for next summer.
Sherwood Peach, providing photographic evidence of why we bother with all this.
Before you begin: gather the supplies
Have everything ready before the first clump comes out. The knife you need will otherwise be in the one place you didn’t look.
Weatherproof plant tags and a permanent garden marker
A notebook or phone for variety names, photos and planting locations
A digging fork or spade, sharp pruners and a sharp knife
Tool disinfectant, used according to its label
A hose, drying trays, clean storage containers and coarse vermiculite
A thermometer for your storage space
1. Label now. Your memory has other plans.
While you can still recognize the flowers, check each plant’s variety name and secure a readable tag to its lower stem. Take a photo of the bloom with its label and record the variety and planting location.
“I’ll remember which one this is” is a lovely thought. Put it on a label anyway.
Keep one labeled clump together through digging, cleaning and dividing. After division, write the name on the dry tubers with a permanent garden marker and label the storage container, too. If you use abbreviations, keep a written key. Future you is not a reliable witness.
An uncertain variety should be labeled “unknown.” There is no shame in a mystery dahlia. There is a problem with confidently giving it someone else’s name.
A name on the tuber gives you another layer of identification. Keep the full name or an abbreviation key with your records.
2. Watch the weather, not just the calendar
A hard frost that blackens the foliage is a useful signal to plan your harvest. Tubers mature late in the season, so give them as much growing time as conditions safely allow, but lift them before the soil freezes. The forecast gets a vote.
For a straightforward home-garden approach, cut the stems to about 4–6 inches just before digging. Hollow cut stems can collect rainwater, so avoid leaving freshly cut plants standing in the ground for days.
3. Dig wide and lift gently
Start about 12–18 inches away from the stem. Loosen the soil on all sides, then work your fork or spade underneath and support the clump as you lift it. Don’t haul it out by the stalk.
The narrow neck connecting a tuber to its crown is fragile. A broken neck can make that tuber unusable, so take your time. This is excavation, not a tug-of-war.
The growing rows at Stony Brook Blooms. Keep the tags with each clump when the digging begins.
4. Clean them up and inspect
If you’ll divide in fall, gently rinse away soil so you can see the crown and look for eyes. Skip the forceful water jet. Trim fine feeder roots and discard tubers with broken necks, mushy tissue or obvious rot.
You can also brush loose soil off intact clumps, store them and divide in spring. Both approaches can work. Whichever you choose, don’t pack wet tubers away, and keep questionable or diseased material separate from healthy stock.
5. Divide for next year’s plants, not a personal record
Each usable division needs a firm tuber body, an intact neck and a piece of crown with at least one viable eye. The eye is the growth bud near the old stem. A beautiful, plump tuber without crown tissue and an eye will not grow into a new plant.
Body + intact neck + crown with a viable eye. Size alone is not a qualification.
Look for small raised buds before cutting. Use a sharp blade to divide the crown into manageable sections, then separate only the tubers whose eyes you can confidently identify. Leave enough crown around each eye rather than cutting close to it.
Fall division can be easier because the clump is less woody. Spring often makes the eyes easier to see. If you’re unsure, leave a larger section or the whole clump and finish later. This is not a timed exam.
Remove debris from your cutting tools and disinfect them between clumps. Follow the product’s directions, including the required contact time.
6. Let the surfaces dry. Don’t make raisins.
Spread cleaned divisions in a sheltered, frost-free place with airflow and no direct sun. Allow surface moisture to disappear and cuts to dry before packing. This often takes a day or two, but humidity and tuber size affect the timing.
Check the tubers rather than relying only on the clock. You want dry surfaces and firm tubers, not badly shriveled specimens.
7. Find a cool, frost-free winter home
One practical starting method is to layer tubers in coarse vermiculite in labeled containers, with enough medium to surround them. Keep varieties separated. The packing should retain moisture without leaving the tubers wet.
Choose a dark, reliably frost-free location around 40–50°F. The American Dahlia Society recommends aiming for 40–45°F. Use a thermometer rather than guessing. A New York garage or shed can freeze, and a warm room can encourage early sprouting.
The goal is dormant dahlias, not frozen dahlias. Those are very different spring outcomes.
Container choice depends on your storage conditions. Watch for condensation and adjust ventilation if the contents stay damp. There isn’t one perfect box for every basement, garage or spare room.
8. Check in occasionally. They’re not entirely independent.
Inspect about once a month. Remove rotting tubers promptly, look for severe shriveling and check the temperature. If they’re drying out, reassess moisture retention. If they’re wet or moldy, reassess moisture and airflow. Avoid soaking them or making the packing soggy.
Keep a few notes about your containers, storage location and results. Next fall, those notes will be considerably more useful than “I think this worked?”
The quick winter checklist
Variety names checked and labels readable
Clumps lifted gently, with their tags
Each division has a body, intact neck and crown with a viable eye
Unhealthy tubers removed
Surfaces and cuts dry before packing
Containers labeled, with an abbreviation key if needed
Storage dark, cool and reliably frost-free
Monthly checks on the calendar
Saving dahlias takes some care, a bit of patience and a willingness to get dirt in places you didn’t know dirt could go. But next summer’s flowers are a pretty convincing argument.
Follow Stony Brook Blooms for more dahlia growing updates and future tuber availability. The flowers may be taking a winter break. The labeling department is not.
Further reading
This original guide draws on horticultural guidance from the following resources. Storage recommendations vary with climate and conditions, so these are useful references as you find a method that works in your space.
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