Table of Contents
- Introduction
- Knowing When to Begin
- To Dig or Not to Dig
- Step 1: Cutting and Curing
- Step 2: Digging with Care
- Step 3: Cleaning and Labeling
- Step 4: Selecting a Storage Medium
- Step 5: Finding the Perfect Storage Spot
- Step 6: Mid-Winter Health Checks
- How to Winter Over Dahlias in the Ground
- Preparing for Spring
- Common Myths About Wintering Dahlias
- Conclusion
- FAQ
Introduction
There is nothing quite like the late-summer satisfaction of a garden filled with dinnerplate dahlias. These spectacular bloomers often become the crown jewels of the backyard, providing armloads of flowers for bouquets from July until the first frost. Because dahlias are native to the warm climates of Mexico and Central America, they cannot survive freezing temperatures in the soil. To enjoy those same beautiful varieties year after year, you simply need to give them a little help during the colder months.
At Longfield Gardens, we want to help you preserve your favorite dahlia varieties so your garden grows more beautiful every season. Learning how to winter over dahlia bulbs—technically known as tubers—is a rewarding skill that saves money and allows you to grow larger, more robust plants each year. This process involves timing your harvest correctly, preparing the tubers for dormancy, and providing the right storage conditions.
This guide will walk you through the entire process of lifting, cleaning, and storing your dahlias. Whether you are a beginner or a seasoned gardener, these steps will help you successfully transition your plants from the garden to the basement and back again. With a little bit of care, those prized tubers will be ready to sprout and shine when the soil warms up next spring.
Knowing When to Begin
Timing is the most important factor when you start the wintering process. If you dig too early, the tubers may not have stored enough energy to survive the winter. If you wait too long, a deep freeze could damage the tuber tissue beyond repair. The goal is to let the plant finish its natural life cycle for the season before you move it into storage.
In most regions, the signal to begin is the first "killing frost." This is the frost that turns the lush green foliage of your dahlias to a dark brown or black. While a light frost might only singe the edges of the leaves, a killing frost tells the plant to move all its remaining energy down into the tubers. We recommend waiting about a week after this frost before you start digging. This short waiting period allows the "eyes" (the growth points) on the tubers to become more visible, which is helpful if you plan to divide them.
If you live in a climate where frost is rare, you can still winter over your dahlias by watching the calendar. Most dahlias will naturally begin to turn yellow and decline as the days shorten in late autumn. Once the plant looks tired and stops producing flowers, you can cut the stems back and proceed with lifting the tubers. The key is to ensure the plant has had a full season of sun to build up its starch reserves.
To Dig or Not to Dig
Before you grab your garden fork, it is helpful to understand your local climate. Whether you need to lift your tubers depends largely on your USDA plant hardiness zone. Dahlias are generally considered hardy in zones 8 through 11. In these warmer areas, the ground rarely freezes deep enough to harm the tubers. Gardeners in these zones can often leave their dahlias in the ground, provided the soil has excellent drainage.
For gardeners in zones 3 through 7, lifting the tubers is a necessity. In these colder regions, the soil temperatures drop well below freezing, which will turn a dahlia tuber into a mushy, non-viable mess. Even in zone 7, where winters are milder, a particularly wet or cold season can lead to rot. If you are unsure about your zone or your soil drainage, lifting and storing the tubers is always the safest option to ensure they return.
The most important rule for dahlia survival is "cool and dry." If the tubers stay too warm, they will sprout or shrivel; if they stay too wet, they will rot. Finding the balance between these two states is the secret to wintering success.
Step 1: Cutting and Curing
The first physical step in the process is removing the top growth. Use a clean pair of bypass pruners or loppers to cut the dahlia stems down to about 4 to 6 inches above the soil line. Leaving a few inches of stem provides a "handle" for moving the clump and helps you keep track of where the tubers are located in the soil. It also gives you a place to attach a label so you don't forget which dahlia variety is which.
After cutting the stems, some gardeners choose to let the tubers "cure" in the ground for a few days. If the weather is dry, this brief period allows the skin of the tubers to toughen up slightly, making them more resistant to nicks and scratches during the digging process. However, if heavy rain is in the forecast, it is better to dig them immediately. Excess moisture can travel down the hollow stems of the dahlia and settle in the crown, which can lead to rot during storage.
What to do next:
- Identify your dahlia varieties and have labels ready.
- Cut stems to 4–6 inches after the first killing frost.
- Dispose of the old foliage in a compost pile or yard waste.
- Check the weather forecast to ensure a dry window for digging.
Step 2: Digging with Care
Dahlia tubers grow in a circular clump just below the soil surface. They are attached to the main stem by a narrow "neck." This neck is very fragile, and if it breaks, the tuber will usually not grow, even if the rest of the tuber is healthy. This is because the growth "eyes" are located on the crown (where the tuber meets the stem), not on the body of the tuber itself.
To dig them safely, start by clearing any mulch away from the base of the plant. Use a garden fork rather than a spade if possible. A fork is less likely to slice through the tubers. Position your fork about 12 inches away from the center of the stem and push it straight down into the soil. Gently pry upward to loosen the roots. Repeat this process in a circle all the way around the plant.
Once the soil is loose, reach under the clump with your hands or the fork and lift the entire root mass out of the ground. Do not pull on the stem to lift the plant, as this can easily snap the necks of the tubers. Lift from underneath and gently shake off the heavy clods of soil. At this stage, the tubers are full of water and very brittle, so handle them as if they were a basket of eggs.
Step 3: Cleaning and Labeling
Once the clumps are out of the ground, you need to decide whether to wash them. There are two schools of thought on this. Some gardeners prefer to wash all the soil off with a garden hose to inspect for pests or rot. Others prefer to leave a little bit of soil on the tubers, believing it provides a natural protective layer.
If your soil is heavy clay, washing is usually necessary because clay holds too much moisture. If you have sandy, loose soil, a gentle shake might be enough. If you do wash your tubers, make sure they dry completely before you put them in a box. Place them in a cool, shaded area (like a garage or shed) for 24 to 48 hours. Lay them upside down so any water trapped in the hollow stems can drain out.
Labeling is a step you should never skip. It is impossible to tell a white dahlia tuber from a purple one once they are out of the ground. You can use a waterproof garden marker to write the variety name directly on the skin of the tuber. Alternatively, use a piece of flagging tape or a plastic tag tied securely to the stem. This ensures that when you go to plant your garden next spring, you can place your large flowering dahlias in the back and shorter ones in the front.
Step 4: Selecting a Storage Medium
Dahlia tubers need a storage environment that is breathable but holds just enough moisture to keep them from shriveling. If you put them in an airtight plastic container, they will likely rot from the trapped moisture. If you leave them out in the open air, they will dry out and turn into hard, useless "mummies." The solution is to pack them in a storage medium that acts as a buffer.
Commonly used storage media include:
- Vermiculite: This is a gold standard for many growers. It is sterile, lightweight, and does an excellent job of regulating moisture.
- Peat Moss: This is an affordable and widely available option. It is naturally acidic, which can help inhibit fungal growth. Ensure the peat moss is slightly damp—not wet—before packing.
- Pine Wood Shavings: Often sold as animal bedding, these are inexpensive and provide great airflow. Avoid cedar shavings, as the oils can sometimes be too harsh for the tubers.
- Coarse Sand: Sand is heavy but provides a very stable environment. It is a good choice if your storage area has fluctuating humidity.
To pack your tubers, find a sturdy cardboard box or a plastic bin with holes drilled in the sides for ventilation. Place a 2-inch layer of your chosen medium at the bottom. Arrange the dahlia clumps so they are not touching each other. This prevents a single rotten tuber from "infecting" its neighbors. Cover the clumps with more storage medium until they are completely buried.
Step 5: Finding the Perfect Storage Spot
The location where you keep your boxes is just as important as how you pack them. You are looking for a spot that is dark, well-ventilated, and stays consistently cool. The ideal temperature range for dahlia storage is between 40°F and 50°F.
An unheated basement, a root cellar, or a crawl space is often the best choice. A garage can work, but you must be careful that the temperature doesn't drop below freezing. If the tubers freeze, they will die. Conversely, if the storage area is too warm (above 55°F), the tubers may think it is springtime and begin to sprout prematurely, which depletes their energy.
Check the temperature of your storage spot with a simple thermometer. If you find the area is a bit too cold, you can wrap your boxes in old blankets or move them further away from exterior walls. If it is too warm, try placing the boxes on the floor, which is usually the coolest part of the room.
What to do next:
- Select a storage medium like vermiculite or peat moss.
- Find a cool, dark storage location (40–50°F).
- Pack tubers in layers, ensuring they do not touch.
- Place a thermometer in the storage area to monitor conditions.
Step 6: Mid-Winter Health Checks
Wintering over dahlias is not a "set it and forget it" project. We recommend checking on your tubers once a month throughout the winter. This allows you to catch small issues before they become big problems. Success rates for overwintering are high, but a little bit of maintenance ensures you lose as few tubers as possible.
When you check your boxes, look for two things: rot and shriveling.
- If you find rot: The tuber will feel soft, mushy, or smell unpleasant. Use a clean, sharp knife to cut away the rotten portion until you see clean, white tissue. If the entire clump is soft, discard it immediately so it doesn't affect other boxes.
- If you find shriveling: This means the storage environment is too dry. The tubers should feel firm, like a fresh potato. If they look wrinkled or feel spongy, lightly mist the storage medium with a spray bottle of water. Do not soak it; just add enough moisture to raise the humidity in the box.
Monthly check-ins are the best way to ensure your dahlia collection stays healthy. A quick mist of water or the removal of one bad tuber can save an entire variety.
How to Winter Over Dahlias in the Ground
If you live in USDA zone 8 or higher, or if you are in zone 7 and feeling adventurous, you might choose to leave your dahlias in the ground. This method significantly reduces the labor involved and often results in larger, earlier-blooming plants the following year. However, it requires a different kind of preparation to protect the tubers from winter rain and occasional cold snaps.
The biggest threat to in-ground dahlias is not just the cold, but the cold combined with wet soil. To succeed, your garden bed must have excellent drainage. In the late fall, cut the stems down to the ground. Cover the entire bed with a thick layer of mulch. This layer should be at least 6 to 12 inches deep. You can use straw, shredded leaves, or wood chips.
For extra protection, some gardeners place a piece of burlap or a waterproof tarp over the mulch layer. This helps shed excess winter rain and snow, keeping the soil beneath relatively dry. When spring arrives and the danger of frost has passed, pull back the mulch to allow the sun to warm the soil. You will likely see new shoots emerging several weeks earlier than you would from newly planted tubers.
Preparing for Spring
As winter winds down and the ground begins to thaw, your dahlias will naturally begin to wake up. In late March or April, you might notice small pink or white "eyes" starting to swell on the crowns of your stored tubers. This is an exciting sign that your wintering efforts have been successful!
If you want to get a head start on the season, you can move your tubers to a warmer, brighter spot indoors about 4 to 6 weeks before your last frost date. You can even start dahlias indoors in containers with a little potting soil to encourage early sprout development. This is also the best time to divide your clumps. Because the eyes are now clearly visible, you can easily see where to make your cuts to ensure every new division has a point of growth.
Wait until the soil in your garden has warmed to at least 60°F before planting your tubers outside. Planting into cold, wet spring soil is a common cause of rot. At Longfield Gardens, we always recommend patience in the spring; dahlias are heat-loving plants, and they will grow much faster once the weather is consistently warm.
Common Myths About Wintering Dahlias
There are many "internet hacks" for storing dahlias, but the traditional methods are usually the most reliable. One common myth is that you must use a fungicide dip before storing. While some professional growers use these, most home gardeners find that simply keeping the tubers dry and cool is enough to prevent fungus.
Another myth is that you must divide your tubers in the fall. While you can certainly do this, the eyes are much harder to see in the autumn. For beginners, we suggest waiting until spring to divide. The tubers are easier to handle, the eyes are prominent, and you can clearly see which parts of the clump have survived the winter.
Finally, don't worry if you lose a few tubers. Even expert gardeners expect a small percentage of loss during the winter. Factors like the health of the plant during the summer, the humidity of your basement, and the specific dahlia variety all play a role. Focus on the ones that thrive and enjoy the beautiful blooms they provide.
Conclusion
Wintering over dahlia bulbs is a simple, satisfying process that bridges the gap between gardening seasons. By following the natural cues of the first frost and providing a cool, stable environment for dormancy, you can preserve your favorite flowers for years to come. Remember that dahlia tubers are resilient; they just need a little help staying dry and frost-free while they rest.
At Longfield Gardens, we believe that gardening should be a rewarding and enjoyable experience. Successfully waking up your dahlias in the spring feels like a victory, and the resulting blooms are a beautiful reward for your efforts. As you gain experience with lifting and storing, you will find a rhythm that works best for your specific climate and storage space.
Key Takeaways for Success:
- Wait for a killing frost before lifting tubers to ensure they have stored enough energy.
- Handle tubers gently to protect the fragile "neck" where growth begins.
- Store in a breathable medium like vermiculite at 40–50°F.
- Check tubers monthly to manage moisture levels and remove any rot.
We look forward to seeing your garden flourish with the spectacular colors and shapes that only dahlias can provide. Happy gardening!
FAQ
How do I know if a dahlia tuber is still alive in the spring?
A healthy tuber should feel firm to the touch, similar to a fresh potato or a carrot. If you see small, pimple-like bumps or tiny green sprouts near the stem, the tuber is definitely alive. If the tuber is completely hollow, mushy, or shriveled like a raisin, it is likely no longer viable and should be discarded.
Can I store dahlia tubers in a refrigerator?
A refrigerator can work if you have no other cool space, but it is often too dry and too cold. Most refrigerators are kept around 35–38°F, which is very close to freezing. If you use a fridge, keep the tubers in the crisper drawer in a bag of damp peat moss, and ensure there is no fruit nearby, as ripening fruit releases ethylene gas that can damage the tubers.
Do I need to wash the dirt off the tubers before storing them?
Washing is a personal preference. It makes the tubers cleaner to handle and easier to inspect for rot, but it also adds moisture that must be dried out before storage. If your soil is loose and sandy, you can simply shake it off. If your soil is heavy clay, washing is usually better to prevent the clay from holding moisture against the tuber skin.
What happens if I don't dig up my dahlias in a cold climate?
In USDA zones 7 and below, the ground usually freezes deep enough to reach the tubers. Since tubers are mostly water, they will freeze, expand, and then turn into a soft, watery mush when the ground thaws. Once a tuber has frozen, it cannot be saved and will not grow back the following year.