Introduction
There is nothing quite like the late-summer glory of a dahlia garden. Whether you love dinnerplate dahlias that command attention or the delicate pompons that brighten up every bouquet, these flowers are a highlight of the growing season. At Longfield Gardens, we enjoy helping gardeners preserve these beautiful plants so they can enjoy them again next year.
This guide is designed for home gardeners who want to know exactly when to lift their tubers to ensure they stay healthy through the winter. We will cover the biological signs of readiness, the impact of your local weather, and how to prepare your dahlias for their winter rest. Knowing the right timing is the secret to keeping your favorite varieties part of your landscape for years to come. If you want another big-blooming option for next season, see the Dahlia Dinnerplate High Summer Mix.
For a refresher on lifting and storing tubers, see our How to Overwinter Dahlias.
The Short Answer: When to Dig Your Dahlias
For most gardeners in the United States, the best time to dig up dahlia tubers is shortly after the first "killing frost" of autumn. A killing frost is when temperatures drop low enough to turn the plant's green foliage black or dark brown. This usually happens in late October or November, depending on your specific location. For a broader timeline from sprout to bloom, see How Long Does It Take for Dahlias to Grow.
While the sight of blackened leaves might look like a failure, it is actually a vital signal. The frost tells the plant that the growing season is over and it is time to go dormant. However, you do not need to rush out with a shovel the very next morning. In fact, most experts recommend waiting about a week to ten days after that first frost before you begin digging.
Why Timing Matters for Tuber Health
Timing is everything when it comes to the long-term health of your dahlias. If you dig them up too early, the tubers may not have enough stored energy to survive the winter. If you wait too long and the ground freezes solid, the tubers can turn to mush and will not sprout in the spring.
The Role of Photoperiodism
Dahlias are sensitive to the length of the day, a biological trait called photoperiodism. When the days begin to shorten in late summer and early autumn, the plant stops putting all its energy into making flowers. Instead, it starts channelling that energy downward into the roots. This is when the tubers really begin to swell and store the starches they need to survive dormancy. For a fuller overview of planting, care, and bloom timing, How to Best Grow Dahlias is a helpful companion.
Tuber Maturity
The tubers need as much time as possible in the soil to mature. A mature tuber has a thicker skin and a higher concentration of nutrients. If you dig them up while the sun is still high and the plant is actively blooming in mid-September, the tubers will be thin-skinned and prone to shrivelling once they are in storage.
The Benefit of the "Wait Period"
Waiting those extra few days after the first frost serves a practical purpose. During this time, the "eyes" of the dahlia—the small bumps that will become next year's stems—often become more visible. This makes it much easier to divide your tubers accurately. Additionally, the skin on the tubers begins to toughen up, making them less likely to be damaged during the digging process.
Key Takeaway: The ideal window for digging is 7 to 14 days after the first killing frost, but before the ground itself freezes.
Reading the Signs: Is It Time to Dig?
Nature provides several clear indicators that your dahlias are ready to be lifted. Keeping an eye on these changes will help you plan your weekend gardening tasks.
Foliage Color
The most obvious sign is the change in foliage. A light frost might only nip the edges of the leaves, but a hard frost will turn the entire plant into a dark, wilted mass. Once the plant looks like it has been "melted" by the cold, it has officially stopped growing for the year.
Soil Temperature
Dahlias are native to the high plains of Mexico, where they do not experience deep-freezing soil. While they can handle a cold snap above ground, the tubers themselves are tender. You want to dig them up before the soil temperature drops below 40°F. If you can still easily push a garden fork into the ground, you are usually in the safe zone. If you're not sure what that means for your area, start with the Hardiness Zone Map.
Flower Production
You may notice that in very late autumn, your dahlia blooms start to look smaller or less vibrant. The plant may produce fewer buds as it naturally begins to wind down. While this isn't a direct signal to dig, it is a reminder that the season is closing and you should have your storage supplies ready.
When to Dig If You Don't Get Frost
If you live in a mild climate (such as parts of California, Florida, or the Pacific Northwest) where a hard frost might not arrive until very late—or at all—you have to look for different cues.
In these regions, the plants may stay green well into December. However, the tubers still need a rest period. If you do not get a killing frost, you can "force" the plant into dormancy in late November or early December by following these steps:
- Stop Watering: Let the soil dry out naturally.
- Cut the Stalks: Use clean shears to cut the plants down to about 4 to 6 inches above the ground.
- Wait Two Weeks: Leave the tubers in the ground for about 14 days. This mimics the post-frost curing period and helps the skins toughen up before you lift them.
Handling Early Winters and Unexpected Weather
Weather is rarely predictable, and sometimes an early winter storm can catch gardeners off guard. If your forecast calls for a deep, ground-freezing freeze before you have had a chance to dig, do not panic.
A single night of cold temperatures will not usually freeze the ground several inches deep. However, if a sustained cold snap is coming, you should prioritize getting your dahlias out of the earth. It is better to dig a few days "too early" than to lose your entire collection to a frozen garden bed.
What to do next:
- Check your local frost dates using an online weather tool.
- Prepare your storage bins and medium (like peat moss or vermiculite) in early October.
- Label your dahlias while they are still in bloom so you know which is which after the foliage dies.
The Digging Process: Step-by-Step
Once the timing is right, you want to lift the tubers carefully. Dahlia clumps can be surprisingly large and heavy, and the "necks" of the tubers—the narrow part where they connect to the main stem—are quite fragile.
Step 1: Cut Back the Stalks
Cut the main stalks down so only about 4 to 6 inches remain. This gives you a "handle" to work with but removes the heavy, messy foliage that makes digging difficult.
Step 2: Use the Right Tools
A garden fork is generally better than a shovel for this task. The tines of a fork are less likely to slice through a hidden tuber than a solid shovel blade. "Drainage" is also easier to manage with a fork, as the loose soil falls through the tines.
Step 3: Give Them Space
Start digging about 12 inches away from the center of the stalk. Digging too close is the most common way tubers are damaged. Gently loosen the soil all the way around the plant before attempting to lift the clump.
Step 4: Lift Gently
Once the soil is loose, slide your fork under the clump and lift it upward. Shake off the excess soil. If the clump is heavy with wet clay, be extra careful, as the weight of the mud can snap the tubers off the stem.
Preparing Tubers for Their Winter Nap
After the tubers are out of the ground, they need a bit of preparation before they go into storage. This ensures they don't rot or dry out completely over the next few months.
Cleaning the Tubers
Some gardeners prefer to wash their tubers with a garden hose to remove all soil, while others prefer to let the soil dry and then gently brush it off. Washing makes it easier to see the "eyes" and check for any signs of damage or rot. If you do wash them, make sure they are allowed to dry thoroughly in a protected, frost-free area for a day or two before packing them away.
Curing and Drying
Curing is the process of letting the outer skin dry and stabilize. Place your lifted clumps in a cool, dry place out of direct sunlight. A garage or a covered porch works well, provided temperatures stay above freezing. Turn the clumps upside down so any moisture trapped inside the hollow stems can drain out.
Labeling Your Collection
This is a step you will be thankful for in the spring. Once the tubers are clean and dry, use a permanent marker to write the name of the variety directly on the skin of the tuber. Alternatively, you can tie a weather-proof tag to the stem. It is very easy to forget which tuber is the Cafe Au Lait once they are all in boxes!
You may have the same problem with Thomas Edison.
Storing Your Dahlias Successfully
The goal of winter storage is to keep the tubers cool and dormant without letting them freeze or shrivel.
The Ideal Environment
The best storage spot is a dark, cool space that stays between 40°F and 50°F. An unheated basement, a crawl space, or a cool closet in a garage usually works perfectly. If the area is too warm, the tubers may start to sprout too early. If it is too cold, they will freeze.
Storage Mediums
To prevent the tubers from drying out, pack them in a material that holds just a tiny bit of moisture but still allows for air circulation. Popular choices include:
- Coarse Vermiculite: Excellent for moisture control.
- Peat Moss: A classic choice, but make sure it is not soaking wet.
- Wood Shavings: Often used for animal bedding, these provide great insulation.
- Dry Sand: Good for heavy-duty protection but can be very heavy to move.
Place a layer of your chosen medium in a cardboard box or plastic bin, lay the tubers on top (not touching each other if possible), and cover them with more medium. If you use plastic bins, leave the lid slightly ajar to prevent moisture from building up and causing mold. The same storage advice works for pompon dahlias, too.
Troubleshooting Common Timing Issues
Sometimes, despite our best efforts, things don't go exactly to plan. Here is how to handle a few common scenarios.
"I dug them up too late and the ground froze!"
Check the tubers immediately. If they are firm and white inside when nicked, they might still be okay. If they feel soft, squishy, or look like they are turning translucent, they have likely frozen and will rot. You can try to save them by cutting away any soft parts, but keep a close eye on them in storage.
"I have to dig them up early because I'm moving."
If you must dig before the frost, try to wait until at least 120 days after they were planted. This gives them the minimum time needed to form viable tubers. They will be more delicate, so handle them with extra care and check on them more frequently during the winter to make sure they aren't shrivelling.
"The stems look moldy after I cut them."
This can happen if it is a very wet autumn. When you cut the hollow stems, they can act like straws, pulling water down into the crown of the plant. If you see signs of mold, cut the stem back a little further until you find clean, healthy tissue. Always store tubers upside down for the first few days to ensure they are fully drained.
Realistic Expectations for Overwintering
It is important to remember that gardening is a partnership with nature. Even with perfect timing and storage, it is normal to lose a few tubers over the winter. Some varieties are simply "better keepers" than others.
Check your stored tubers once a month. If you see one that is getting soft or fuzzy with mold, remove it immediately so the problem doesn't spread to the healthy ones. If they look very shrivelled, you can give the storage medium a very light misting of water—just enough to add a hint of humidity, not enough to make it wet. If anything seems off, our 100% Quality Guarantee is there to back you up.
Conclusion
Digging up dahlia bulbs at the right time is one of the most rewarding tasks in the garden calendar. By waiting for the first frost and allowing the tubers a short curing period in the soil, you are giving your plants the best possible chance at a successful winter rest. Whether you are a seasoned grower or a beginner, following these simple timing rules makes the process straightforward and achievable.
At Longfield Gardens, we believe that every gardener can enjoy the spectacular beauty of dahlias year after year. With a little patience and the right environmental cues, you'll be ready to tuck your tubers away safely, knowing they'll be ready to dazzle again next summer.
- Wait for the foliage to turn black after the first frost.
- Wait 7–14 days for the skins to toughen and eyes to appear.
- Dig carefully with a fork, starting 12 inches from the stem.
- Store in a cool, dark place between 40°F and 50°F.
Success with dahlias comes down to watching the weather and trusting the plant's natural signals. When you get the timing right, you ensure a vibrant, colorful garden for many seasons to come.
FAQ
Can I leave my dahlias in the ground all winter?
This depends on your USDA hardiness zone. If you live in Zone 8 or warmer, you can often leave dahlias in the ground if you provide a thick layer of mulch (about 4–6 inches) to protect them from occasional cold snaps. In Zone 7 and colder, the ground usually freezes deep enough to kill the tubers, so digging them up is necessary.
How do I know the difference between a light frost and a killing frost?
A light frost usually occurs when temperatures are right at 32°F; it may only damage the top-most leaves or the open flowers. A killing frost occurs when temperatures stay below freezing for several hours, usually reaching 28°F or lower. This will turn the entire plant brown or black and cause the stems to collapse.
What happens if I dig my dahlias before the first frost?
If you dig them too early, the tubers may be "immature," meaning they haven't finished storing enough starches or developing a thick enough skin. These tubers are much more likely to shrivel and die during winter storage. If you must dig early, try to wait as late into the autumn as possible to give them maximum growth time.
Should I divide my dahlias in the fall or the spring?
Both methods work! Dividing in the fall is often easier because the tubers are softer and you have more time. However, dividing in the spring is safer for beginners because the "eyes" (the growth points) are much easier to see after the tubers have had a winter rest. If you aren't sure where to cut, wait until spring.
