Introduction
Dahlias are the undisputed stars of the late-summer garden. Their bold shapes and vibrant colors provide a sense of joy just as other plants begin to fade. For many of us at Longfield Gardens, the peak of dahlia season is the most rewarding time of the year. To keep that beauty coming back season after season, it is important to know when and how to transition these plants from the garden into winter storage.
If you live in a climate where the ground freezes, lifting your tubers is a simple way to protect your investment and save your favorite dahlia collections. This process allows you to save your favorite varieties and even increase your collection over time. Knowing the right moment to start is the first step toward a successful growing season next year.
In this guide, we will focus on exactly when to dig up dahlia tubers based on your local weather and plant signals. For more dahlia basics, see All About Dahlias. We will also cover the steps to take once they are out of the ground to ensure they stay healthy until spring. By following a few straightforward steps, you can confidently preserve your dahlias for years of future blooms.
Understanding the Dahlia Lifecycle
To understand when to dig up dahlia tubers, it helps to look at what is happening underground. During the summer, the plant puts most of its energy into growing stems, leaves, and those spectacular flowers. As the days grow shorter in late summer and early fall, the dahlia’s priorities shift.
The plant begins to transition into a storage phase. It starts sending starches and sugars down into the root system. This energy is stored in the tubers, which act like batteries for the following year. These tubers need time to mature and bulk up before they are ready for a long winter nap.
The timing of this process is mostly driven by light. When there are fewer than 12 hours of daylight, the plant receives a biological signal to stop making new flowers and start preparing for dormancy. This is why digging too early in the summer is rarely successful; the tubers haven't had enough time to build up the necessary energy reserves.
The Role of Frost in Tuber Harvest
The most common question gardeners ask is whether they must wait for a frost before digging. While a light frost is a helpful signal, it is not the only factor. A frost serves as a clear "stop" command for the plant's top growth. Once the foliage turns black or brown from the cold, the plant is officially finished for the season.
Waiting for this first frost is beneficial because it ensures the plant has squeezed every bit of energy out of the leaves and into the tubers. However, in some regions, a hard freeze might arrive very late, or the soil might become dangerously wet before a frost occurs. If your garden stays warm but the calendar says it is late autumn, you can still dig your tubers.
Most dahlias are ready for harvest once they have been in the ground for at least 120 days. If a frost has not arrived by late October or early November in your area, you can choose to move forward with the harvest regardless. The goal is to get the tubers out of the ground while the soil is still workable and before it becomes a cold, muddy slurry.
The Two-Week Rule for Curing
One of the most effective tricks for successful storage is the "two-week rule." After the first light frost hits and the foliage wilts, many experienced growers wait about 10 to 14 days before lifting the tubers from the soil. This short waiting period serves a specific purpose.
During these two weeks, the tubers go through a process called curing. While they sit in the cooling soil, their outer skins begin to toughen and thicken. This "winter skin" is much more resilient than the tender skin found on a growing tuber. A thicker skin helps prevent the tuber from drying out or shriveling once it is moved into a box or bag for storage.
If you dig immediately after the frost, the skins may be soft and easily damaged. Scratches or nicks on a soft tuber provide an entry point for rot. By giving them those extra few days in the ground, you are helping the dahlia protect itself. Just keep an eye on the weather; if the forecast calls for a deep, ground-penetrating freeze, it is better to dig a little early than to let the tubers freeze in the dirt.
Timing Based on Your Climate and Zone
Your specific location in the United States plays a major role in your dahlia harvest timeline. We use USDA plant hardiness zones to help determine when plants can stay in the ground and when they need a little extra help.
Cold Climates (Zones 3-6)
In these northern regions, the ground will freeze solid during the winter. Dahlias cannot survive these temperatures and must be dug up every year. Typically, the harvest happens between late September and late October. Gardeners in these zones often see their first frost around this time, making the timing very straightforward.
Moderate Climates (Zone 7)
Zone 7 is a transitional area. In a mild winter, dahlias might survive if they are buried under a thick layer of mulch. However, if the winter is particularly wet or cold, the tubers may rot or freeze. To be safe, we usually recommend digging up dahlias in Zone 7 to ensure they remain healthy.
Warm Climates (Zones 8-11)
In the South and along the West Coast, dahlias can often stay in the ground year-round. However, "when to dig" might still be a relevant question if your soil does not drain well. In rainy winter climates, tubers can rot even if the temperature stays above freezing. Some gardeners in these zones dig their tubers every two or three years simply to divide them and prevent the clumps from becoming too crowded.
Key Takeaway: The best time to dig is generally 10 to 14 days after the first light frost, or in late October if no frost has occurred. Aim to harvest before the soil becomes excessively wet or the temperature drops below 30°F for several nights in a row.
How to Prepare Your Dahlias for Digging
Once you have decided the time is right, there are a few preparation steps that make the job much easier. A little bit of organization now will save you a lot of confusion when it comes time to replant in the spring.
First, make sure your labels are in place. Before the foliage dies back completely, double-check that every plant has a tag. Once the stems are cut and the leaves are gone, it is almost impossible to tell a Café au Lait from a similar clump just by looking at the tubers.
It is just as true for Cornel. Use a waterproof marker to ensure the names stay legible through the winter.
Next, cut the stalks. We recommend leaving about 4 to 6 inches of the main stem attached to the tuber clump. This remaining stem serves as a handle, making it much easier to lift the clump without damaging the fragile "neck" of the tubers. Be aware that dahlia stems are hollow. After you cut them, they may contain some water. This is normal and will be addressed during the drying phase.
What to do next:
- Check and secure all variety labels.
- Cut the stems down to 4–6 inches above the soil line.
- Gather your tools, such as a garden fork and a set of crates or boxes.
- Clear away any support stakes or netting used during the summer.
A Step-by-Step Guide to Lifting Tubers
Lifting dahlia tubers is a gentle process. While the tubers look like sturdy potatoes, they are actually quite delicate, especially where the tuber connects to the main stem. This area is called the "neck," and if it breaks, the tuber may not be able to sprout next year.
The best tool for the job is a garden fork rather than a shovel. A fork allows the soil to fall through the tines, which reduces the weight you have to lift and minimizes the risk of accidentally slicing through a tuber.
- Start Wide: Place your garden fork about 12 inches away from the center of the stalk. Digging too close is the most common way tubers get damaged.
- Loosen the Soil: Gently push the fork into the ground and rock it back and forth. Do this on all four sides of the plant to loosen the entire root zone.
- Lift Carefully: Once the soil is loose, slide the fork deep under the clump and lift upward. Use one hand to stabilize the stem while the fork does the heavy lifting.
- Remove Excess Dirt: Gently shake the clump or use your fingers to brush away large clods of soil. Do not bang the tubers against a hard surface, as this can cause bruising.
Cleaning and Initial Curing Before Storage
After the tubers are out of the ground, they need a short period of cleaning and drying before they go into their winter containers. There are two schools of thought on cleaning: washing with a hose or simply brushing off the dry dirt.
Many gardeners prefer to wash their tubers. This makes it much easier to see the "eyes" (the small bumps where next year's growth will start) if you plan on dividing the clumps in the fall. Washing also removes soil-borne pests or fungi. If you choose to wash them, use a gentle stream of water and try not to saturate the hollow stems.
After cleaning, the tubers need to dry. This is a critical step. Find a cool, shaded spot with good airflow—a garage, shed, or covered porch works well. Turn the clumps upside down so any water trapped in the hollow stems can drain out. Let them sit for 24 to 48 hours. You want the surface of the tubers to feel dry and the remaining soil to be crumbly, but you do not want the tubers to start shriveling. For more details, see How to Store Dahlia Bulbs Over the Winter.
"Proper drying is the bridge between a healthy harvest and successful storage. Giving the tubers a day or two to air out ensures that excess moisture won't lead to rot during the winter months."
Dividing: Fall or Spring?
A common debate among dahlia lovers is whether to divide the tubers right after digging or wait until spring. Both methods work well, and the choice often depends on your schedule.
Dividing in the fall is often easier because the tubers are softer and more pliable. It also saves space in storage since you are only keeping the viable tubers rather than the entire large clump. However, the "eyes" can be very difficult to see in the fall. These tiny growth points are often dormant and flat against the crown.
If you are a beginner, waiting until spring to divide might be the better option. As the weather warms up in March or April, the eyes will begin to swell and turn pink or green. This makes it very clear where to make your cuts. At Longfield Gardens, we often suggest that new gardeners wait for these visible signals to ensure every division has the potential to grow.
Simple Storage Basics
Once your tubers are dry and labeled, they need a cozy place to spend the winter. The goal of storage is to keep the tubers dormant but alive. This requires a balance of temperature and moisture.
The ideal storage temperature is between 40°F and 50°F. If it is too warm, the tubers will think it is spring and start to sprout. If it is too cold, they will freeze and turn to mush. An unheated basement, a cool closet, or an insulated crawl space are often perfect spots.
To keep the tubers from shriveling, most gardeners store them in a "medium." Common choices include:
- Coarse sand
- Wood shavings (the kind used for animal bedding)
- Vermiculite
- Slightly damp peat moss
Place a layer of your chosen medium in a cardboard box or a plastic bin with a few air holes. Lay the tubers inside so they aren't touching, and cover them with more medium. This helps maintain a consistent level of humidity around the roots.
Monitoring Your Tubers Through Winter
Gardening doesn't completely stop once the plants are in boxes. It is a good idea to check on your stored dahlias about once a month. This small effort can prevent a minor issue from becoming a big problem.
Different varieties may store differently. Some are naturally "good keepers," while others are more prone to drying out.
If you love rounded forms, ball dahlias are another shape worth exploring for next season.
When you check them, look for two things: rot and shriveling. If you find a tuber that feels soft or smells bad, remove it immediately so the rot doesn't spread to its neighbors. If the tubers look wrinkled or feel like a soft sponge, they are too dry. You can lightly mist the storage medium with a spray bottle of water to add a touch of moisture.
Remember that different varieties may store differently. Some are naturally "good keepers," while others are more prone to drying out. By checking in on them periodically, you can adjust your methods and ensure a high success rate.
Preparing for the Next Season
As winter begins to fade, you can start looking forward to the excitement of a new growing season. Digging and storing your tubers is a rewarding cycle that connects you to the history of your garden. Each tuber you save is a piece of the past that will bring beauty to your future.
When you see the first signs of spring, you can pull your boxes out of storage and begin the process of waking them up. If you want a step-by-step refresher, see How to Plant and Grow Dahlia Tubers.
Our team works with growers to provide a wide range of shapes and sizes, and tiny PomPon Dahlias are one end of that spectrum.
On the other end, dinnerplate dahlias deliver massive blooms to the garden.
The time and care you put into harvesting your dahlias now will pay off in a spectacular display of blooms next summer. Gardening is all about these rhythms of growth and rest, and mastering the timing of the dahlia harvest is a wonderful way to grow as a gardener.
Conclusion
Knowing when to dig up dahlia tubers is one of those essential gardening skills that becomes easier every year. By watching for the signals of frost and giving your plants a little time to cure in the ground, you set the stage for a successful winter. Whether you are a seasoned pro or a first-time dahlia grower, the process of lifting and storing these beautiful plants is a satisfying way to wrap up the garden season.
- Wait for a light frost or late October to begin the harvest.
- Allow tubers to cure for 10-14 days in the soil if possible.
- Dig carefully with a garden fork to protect the tuber necks.
- Store in a cool, dark place between 40°F and 50°F.
We at Longfield Gardens are proud to support your gardening journey with high-quality tubers and practical advice, backed by our 100% Quality Guarantee. We hope these tips help you enjoy your dahlias for many years to come.
"The effort you put into your garden today is an investment in the beauty of tomorrow. Saving your dahlias is a wonderful way to keep your favorite memories blooming year after year."
FAQ
Can I dig up my dahlias if they haven't been hit by frost yet?
Yes, you can dig up dahlia tubers before the first frost if your growing season is coming to an end. This is often necessary in regions with long, wet autumns where the soil might become too saturated. As long as the plants have been growing for at least 120 days, the tubers should be mature enough to survive storage.
What happens if I leave my dahlias in the ground over winter?
If you live in USDA Zones 3 through 7, the ground will likely freeze deep enough to kill the tubers. They will turn into a soft, watery mush and will not grow back in the spring. In warmer zones (8 and above), they may survive, but they are still at risk of rotting if the soil stays cold and wet for long periods.
Why do I need to leave a few inches of stem on the tubers?
Leaving 4 to 6 inches of stem provides two main benefits. First, it acts as a handle that allows you to move the heavy clump without putting pressure on the fragile necks of the tubers. Second, as the clump dries, the remaining stem helps the crown stay intact. Just be sure to store them upside down initially to let any trapped water drain out.
How do I know if a dahlia tuber has rotted during storage?
A healthy tuber should feel firm, similar to a fresh potato or a carrot. If a tuber feels mushy, looks slimy, or has a pungent, unpleasant odor, it has likely rotted. If you see white or grey fuzzy mold on the surface, you can often wipe it off and increase the airflow in your storage container, but any truly soft tubers should be discarded immediately.
