Introduction
There is nothing quite like the late-summer glory of a dahlia garden. From the massive dinnerplate dahlias to the perfectly symmetrical pompons, these plants provide a spectacular finale to the growing season. At Longfield Gardens, we believe that one of the most rewarding parts of growing dahlias is knowing you can enjoy those same beautiful flowers year after year.
The perfectly symmetrical pompons are another favorite for a bouquet.
Because dahlias are tender perennials, they cannot survive the freezing winter temperatures found in most parts of the United States. While they are perfectly happy staying in the ground in warmer climates, gardeners in cooler regions need to lift and store the tubers once the season ends. This process, often called "overwintering," allows you to protect your investment and even increase your collection as the plants naturally multiply.
This guide will walk you through the simple, step-by-step process of digging up your tubers, preparing them for their winter nap, and storing them safely. Whether you are a first-time dahlia grower or a seasoned gardener looking to refine your technique, these practical tips will ensure your tubers stay healthy and ready for a fresh start next spring. Learning how to preserve these plants is an easy way to build a more sustainable and vibrant garden.
Understanding Why We Dig Dahlia Tubers
Dahlias are native to the high plains of Mexico and Central America, where the ground does not freeze. In the United States, they are typically hardy only in USDA zones 8 through 11. If you live in zone 7 or colder, the frozen soil of winter will cause the moisture-rich tubers to turn to mush. If you’re unsure of your growing zone, check the Hardiness Zone Map. Digging them up is the only way to ensure they return.
Even if you live in a marginal zone where the ground only freezes lightly, digging has other benefits. Dahlias are vigorous growers. A single tuber planted in May can turn into a massive clump of five to ten tubers by October. By digging them up, you have the opportunity to divide these clumps. This prevents the plants from becoming overcrowded, which leads to better airflow and more prolific blooming in future seasons.
The goal of digging and storage is to keep the tuber in a state of dormant "stasis." You want to keep it cool enough so it doesn't sprout, but warm enough so it doesn't freeze. You also need to manage moisture: too much leads to rot, while too little causes the tuber to shrivel and die. Mastering this balance is the key to a successful spring planting.
Identifying the Right Time to Dig
Timing is one of the most important factors when learning how to dig up dahlia tubers for winter. If you dig too early, the tubers may not have stored enough energy to survive the long winter months. If you wait too long and the ground freezes solid, you risk losing the tubers entirely.
The Signal of the First Frost
The most common signal to begin the process is the first "killing frost." This is the night when temperatures drop low enough to turn the dahlia's lush green foliage into a blackened, wilted mess. While it might look a bit sad to see your beautiful plants succumb to the cold, this is actually a helpful transition.
When the top growth dies back, the plant stops sending energy upward to produce flowers. Instead, it shifts all its resources into the tubers underground. This final burst of energy helps the tubers "ripen" and prepares them for dormancy. Most experts recommend waiting about three to seven days after the first frost before you start digging. This short waiting period allows the "eyes" (the small buds that will become next year's stems) to become more prominent and the skins of the tubers to toughen up.
Alternatives if Frost is Late
In some years, a killing frost may not arrive until very late in the season. If it is mid-November and you haven't had a frost yet, it is usually best to move forward with digging anyway. You want to ensure you have a window of relatively dry, workable weather before the deep winter freeze sets in. You can manually signal the plant to go dormant by cutting the stems down to about six inches above the soil line and waiting a week before lifting the tubers.
Key Takeaway: Wait for the first frost to turn the foliage black. This signals the plant to move its energy into the tubers for better winter survival.
Preparing the Plants for Lifting
Before you grab your shovel, there are a few preparation steps that make the job much easier. Proper preparation helps you stay organized and reduces the risk of damaging the fragile tuber clumps.
Cutting Back the Stems
Once the foliage has blackened from the frost, use a pair of sharp loppers or garden shears to cut the main stalks. You should leave a "handle" of about four to six inches of stem protruding from the ground. This handle is essential for two reasons: it shows you exactly where the center of the clump is located, and it gives you something to hold onto as you gently lift the clump out of the soil.
Labeling Your Varieties
It is remarkably easy to forget which dahlia is which once the flowers are gone and the foliage is brown. Before you lift the clumps, ensure each one is clearly labeled. You can use waterproof garden markers to write the variety name directly on the stem handle, or attach a plastic nursery tag with a zip tie or string.
Because we work with many different dahlia collections at Longfield Gardens, we often find that labeling at this stage is the best way to keep your garden plan organized for next year. If you plan to divide your tubers later, having the name firmly attached to the clump prevents any "mystery" dahlias in the spring.
Cleaning the Area
Clear away the fallen, blackened foliage and compost it, provided the plants were healthy. If you noticed any signs of powdery mildew or viral issues during the summer, it is better to dispose of the foliage in the trash rather than the compost pile to avoid spreading pathogens. A clean workspace makes it easier to see what you are doing and prevents you from accidentally stepping on hidden tuber clumps.
The Proper Technique for Digging Tubers
Dahlia tubers are surprisingly fragile. They are often compared to potatoes, but their "necks"—the thin part where the tuber connects to the central stem—are very easy to snap. If the neck breaks, the tuber usually won't grow because the "eye" is located on the crown (the area where the stem meets the tuber), not on the tuber body itself.
Choosing the Right Tools
A sturdy garden fork (sometimes called a pitchfork) is generally the best tool for the job. The tines of a fork can slide through the soil with less resistance than a solid shovel blade, reducing the likelihood that you will accidentally slice a tuber in half. If you only have a shovel, ensure it is sharp and that you are extra cautious with your placement.
The 12-Inch Rule
The most common mistake beginners make is digging too close to the stem. Dahlia clumps can grow quite wide, often extending 8 to 12 inches out from the main stalk.
- Position your fork about 12 inches away from the stem handle.
- Push the fork straight down into the soil.
- Gently pry upward to loosen the earth.
- Repeat this process in a circle all the way around the plant.
Lifting the Clump
Once you have loosened the soil on all sides, you can begin to lift. Insert the fork deeply under the clump and use a gentle levering motion. Use one hand to steady the stem handle while the other works the fork. Avoid "yanking" the plant out by the stem; instead, let the tool do the heavy lifting from underneath. As the clump clears the ground, lift it out and set it gently on the soil surface.
Key Takeaway: Always dig at least 12 inches away from the stem to avoid slicing the tubers. Use a garden fork to gently pry the clump upward rather than pulling it by the stalk.
Cleaning and Curing Your Tubers
Once the tubers are out of the ground, they need a little bit of "spa treatment" before they go into storage. This stage involves removing excess soil and allowing the tubers to dry out slightly. For a deeper walkthrough, see How to Preserve Dahlia Tubers.
Removing Excess Soil
How much you clean your tubers depends largely on your soil type. If you have light, sandy soil, you can often just shake the clump or use your hands to brush away the dirt. If you have heavy clay soil, the dirt may be stuck in tight clods between the tubers.
Many gardeners prefer to use a gentle stream from a garden hose to wash the tubers clean. This makes it much easier to see the "eyes" and identify any signs of rot or insect damage. However, if you wash your tubers, you must be extremely diligent about drying them afterward. Moisture trapped in the crevices of the clump is the primary cause of winter rot.
Trimming and Inspection
While the tubers are fresh out of the ground, perform a quick inspection.
- Remove "Mother" Tubers: The original tuber you planted in the spring (the mother tuber) often looks darker and may feel slightly soft or "corky." These usually don't store well and can be a source of rot, so many gardeners choose to trim them away.
- Clip Hair Roots: Small, spindly roots hanging off the main tubers can be trimmed back with clean scissors.
- Check for Damage: If you accidentally sliced a tuber with your fork, you can usually leave it as long as the cut is clean. If a tuber is hanging by a thread or has a broken neck, it is best to remove it now.
The Curing Phase
"Curing" is simply the process of letting the tubers dry in a protected area. This allows the skin to toughen up, which protects the moisture inside. Place your tubers in a frost-free location with good air circulation, such as a garage, shed, or basement.
Avoid placing them on a cold concrete floor, as this can draw moisture out of them too quickly. Instead, lay them on a piece of cardboard, a wooden pallet, or a mesh screen. Let them dry for 24 to 48 hours. They should feel dry to the touch, but not shriveled. If you washed them with a hose, they may need an extra day to ensure the hollow stems are completely dry.
To Divide or Not to Divide?
One of the biggest debates among dahlia enthusiasts is whether to divide the tuber clumps in the fall or wait until the spring. Both methods have advantages, and the right choice depends on your schedule and storage space.
Dividing in the Fall
In the autumn, the tubers are relatively soft and easy to cut. If you have a large collection and limited storage space, dividing now saves a significant amount of room. You can cut the clump into individual tubers, ensuring each one has a piece of the "crown" (the area of the stem where the eye is located).
The downside of fall division is that the eyes can be very difficult to see. They often look like tiny, dormant bumps or "pimples." If you can't see the eyes, you risk cutting tubers that will never sprout.
Dividing in the Spring
Many gardeners prefer to store the clumps whole and divide them in the spring. By March or April, the eyes begin to swell and may even start to show a tiny bit of green or pink. This makes it very obvious where to make your cuts. Storing whole clumps also provides a "safety net"—if one tuber in the clump rots, the others may still be perfectly healthy. The trade-off is that whole clumps take up much more storage space and the tissue becomes much harder and "woody" over the winter, requiring more effort to cut.
What to do next:
- Decide if you have enough space to store whole clumps or if you need to divide now.
- If dividing, use a sharp, sterilized knife and ensure every piece has a bit of the crown.
- If waiting until spring, simply proceed to the final packing steps.
Packing Tubers for Winter Storage
The goal of storage is to create a "microclimate" that remains stable for five or six months. You are looking for a spot that is dark, cool, and consistently between 40°F and 50°F. For a fuller step-by-step guide, see How to Lift and Store Dahlia Bulbs.
Choosing a Storage Medium
To prevent the tubers from drying out completely, we recommend packing them in a moisture-regulating material. Popular choices include:
- Pine Shavings: Often sold as animal bedding, these provide great aeration and light moisture retention.
- Vermiculite: A mineral that is excellent at holding a tiny amount of moisture while preventing rot.
- Peat Moss or Coco Coir: These are traditional choices, though you should ensure they are slightly damp (like a wrung-out sponge) but not wet.
- Newspaper: Wrapping individual tubers in several layers of dry newspaper is a simple, low-cost method.
Containers for Storage
You want a container that allows for a small amount of gas exchange so the tubers can "breathe." Cardboard boxes, plastic storage bins with the lids left slightly ajar, or wooden crates are all excellent options.
- Start with a two-inch layer of your chosen storage medium at the bottom of the container.
- Lay the tubers (or clumps) in the box so they are not touching each other. This prevents rot from spreading from one tuber to the next.
- Cover with more storage medium.
- Repeat layers until the box is full, finishing with a thick layer of medium on top.
Finding the Best Location
An unheated basement, a root cellar, or a cool closet in a mudroom are usually the best spots. Avoid garages that might drop below freezing during a polar vortex, as a single night of freezing temperatures can kill the tubers. Similarly, avoid spots near a furnace or water heater, as the heat will cause the tubers to shrivel or sprout prematurely.
Winter Maintenance and Troubleshooting
Storing dahlia tubers isn't quite a "set it and forget it" task. For the best results, you should check on your "babies" about once a month throughout the winter. This allows you to catch small issues before they become big problems.
Checking for Rot
If you see a tuber that looks fuzzy, black, or feels mushy, it is experiencing rot. Remove it immediately and throw it away. If it is part of a larger clump, use a clean knife to cut out the rotten section until you see clean, white tissue. Then, leave the clump out to dry for a day before putting it back into storage.
Checking for Shriveling
If the tubers look wrinkled or feel lightweight and "hollow," they are losing too much moisture. This is a sign that your storage area is too dry or your packing material isn't holding enough humidity. To fix this, you can lightly mist the storage medium with a spray bottle of water. Do not soak the tubers; you just want to add a tiny bit of humidity back into the air inside the box.
Managing Early Sprouting
If you notice small green shoots appearing in February or March, your storage area is likely too warm. Move the containers to a cooler spot if possible. Early sprouts aren't a disaster—you can often just leave them alone—but they do use up the tuber's stored energy.
Planning for Spring
As the days begin to lengthen in late March or early April, it is time to start thinking about the upcoming season. Digging and storing your tubers is a cycle that connects one summer to the next.
When the soil in your garden warms to about 60°F and the danger of frost has passed, you can bring your tubers out of storage. You might notice they look a little bit "sleepy," but once they hit warm soil and receive a bit of water, they will wake up quickly.
By following these steps, you have ensured that your favorite dahlia varieties—perhaps that stunning Cafe Au Lait—will return to provide another season of joy.
The vibrant Cornel is another favorite that can return to provide another season of joy. Our team at Longfield Gardens is always thrilled to hear about successful overwintering stories because it means your garden is growing in both size and beauty.
Conclusion
Digging up dahlia tubers for the winter may seem like a big task at first, but it quickly becomes a rhythmic and satisfying part of the gardening year. By waiting for the frost, digging carefully, and providing a cool, stable environment for storage, you are giving your plants the best possible chance for a long and healthy life.
Key Takeaways for Success:
- Timing: Wait for the first killing frost to signal dormancy.
- Care: Use a garden fork and dig wide to protect the fragile necks of the tubers.
- Curing: Ensure tubers are dry to the touch before packing them away.
- Environment: Aim for a storage temperature between 40°F and 50°F with consistent humidity.
Gardening is a journey of learning and observation. Every climate is slightly different, and you may find that one storage medium works better in your home than another. Don't be afraid to experiment and find the "sweet spot" that works for your specific conditions. We invite you to explore our other guides for more tips on making your garden the most beautiful it can be. Happy gardening, and we look forward to seeing your dahlias bloom again next summer!
FAQ
Can I leave my dahlias in the ground if I use extra mulch?
In USDA zones 8 and warmer, a thick layer of mulch (about 4–6 inches) is usually enough to protect dahlia tubers through the winter. In zone 7, this is a gamble that depends on the severity of the winter and how well your soil drains. In zones 6 and colder, mulch will not prevent the deep ground freeze from reaching the tubers, so digging them up is necessary.
What should I do if I accidentally sliced a tuber while digging?
Accidental nicks and slices are very common and usually aren't a problem. If the cut is clean, simply let the tuber dry and "callous over" during the curing phase. If the tuber is badly mangled or the neck is broken, it is better to remove that specific tuber from the clump to prevent it from rotting in storage.
Why did my tubers rot even though I kept them in a dry place?
Rot is often caused by moisture trapped inside the clump rather than external humidity. This is common if the tubers were washed and not allowed to dry completely, especially in the hollow centers of the stems. To prevent this, always store tubers upside down for the first day of curing to let any water drain out of the stalks.
When is the best time to start my stored tubers in the spring?
You can start your tubers indoors in pots about 4–6 weeks before your last expected frost date if you want an early start on blooms. For planting details, see How to Plant Dahlias. Otherwise, wait to plant them directly in the garden until the soil is warm (at least 60°F) and all danger of frost has passed. Planting in cold, wet spring soil can cause the dormant tubers to rot before they have a chance to grow.
