How to Keep Dahlia Bulbs Over the Winter

Table of Contents

1. Introduction
2. Understanding the Dahlia Life Cycle
3. When to Dig Your Dahlia Tubers
4. Preparing the Plants for Lifting
5. How to Lift Tubers Without Damage
6. Cleaning and Drying the Tubers
7. Identifying Healthy Tubers for Storage
8. To Divide or Not to Divide
9. Choosing the Right Storage Media
10. Ideal Storage Conditions
11. Packing Your Tubers for the Winter
12. Winter Maintenance and Monitoring
13. Overwintering in the Ground (Zones 8-11)
14. Bringing Dahlias Out of Storage
15. Successful Storage Starts with Healthy Plants
16. Conclusion
17. FAQ

Introduction

There is nothing quite like the sight of a dinnerplate varieties in full bloom. From the massive, intricate petals of dinnerplate varieties to the perfectly geometric shapes of pompon types, these flowers are the undeniable stars of the summer and autumn garden. At Longfield Gardens, we believe that the joy of growing dahlias shouldn't have to end when the first frost arrives. While these plants are native to the warm climates of Mexico and Central America, you can easily save your favorite varieties to plant again next year.

This guide is designed for home gardeners who want a reliable, step-by-step process for overwintering dahlia tubers. We will cover when to start the process, how to lift the tubers from the ground without damaging them, and the best ways to pack and store them until spring. By following a few simple steps, you can turn a single season of color into a lifetime of beautiful garden displays. With the right care, your dahlia collection can grow larger and more impressive every year.

Understanding the Dahlia Life Cycle

To keep your dahlias healthy through the winter, it helps to understand what is happening beneath the soil. While we often call them "bulbs," dahlias actually grow from dahlia tubers. These are thickened, underground roots that store energy and moisture for the plant. During the summer, the plant uses this energy to produce lush foliage and heavy blooms. As the days grow shorter and the temperatures drop, the plant shifts its focus back to the tubers, packing away nutrients for the next growing season.

In warm climates—specifically USDA hardiness zones 8 through 11—dahlias can often stay in the ground year-round. However, in most of the United States, the ground freezes deep enough to kill the tubers. For those of us in zones 3 through 7, "lifting" the tubers is a necessary part of the autumn routine. If you're not sure of your zone, the Hardiness Zone Map can help. This process ensures the tubers stay dormant, dry, and safe from the killing bite of a hard freeze.

When to Dig Your Dahlia Tubers

Timing is everything when it comes to overwintering success. If you dig too early, the tubers may not have stored enough energy or developed a thick enough "skin" to survive storage. If you wait too long, a deep freeze could turn the tubers into mush.

The most common signal to begin is the first "killing frost." This is the frost that turns the green foliage of your dahlias to black or dark brown. While it might look a bit sad, this is actually a helpful milestone. The frost tells the plant that the growing season is over and it is time to go dormant.

The Waiting Period

After the first frost hits, many gardeners prefer to wait about 5 to 7 days before digging. During this week, the tubers undergo a final "curing" process in the soil. They begin to develop the eyes (the small buds that will become next year's stems) and the outer skin toughens slightly. If your weather forecast predicts a hard freeze (temperatures staying well below 28°F for several hours), you should proceed with digging immediately rather than waiting. For step-by-step help, see How to Overwinter Dahlias.

Handling Late Seasons

In some years, a killing frost may arrive very late. If you reach mid-November and your plants are still green but the ground is getting cold, you can manually trigger dormancy. Simply cut the plants down to about 4 inches above the soil line and wait a few days before digging. This achieves the same goal as a natural frost by signaling to the tuber that it is time to rest.

Key Takeaway: The best time to dig is right after the first frost has blackened the foliage. This ensures the tubers are fully mature and ready for their winter rest.

Preparing the Plants for Lifting

Before you pick up a shovel, you need to clear the way. Start by cutting the stems down to about 4 to 6 inches above the soil. These short "stumps" serve two purposes: they make the clump easier to handle, and they act as a handle for the variety tags.

Labeling Your Dahlias

One of the most common mistakes in dahlia care is forgetting which tuber is which. Once the tubers are out of the ground, they all look remarkably similar. Use a waterproof pen or garden marker to write the variety name on a plastic tag. You can tie this tag securely to the 6-inch stem stump. Alternatively, some gardeners write the name of the variety directly on the skin of a clean, dry tuber using a soft pencil or permanent marker later in the process.

Tool Selection

Avoid using a standard pointed shovel if possible. A garden fork (also called a pitchfork) is much safer for lifting tubers. The tines of the fork allow soil to fall through and are less likely to slice through the tubers than a solid shovel blade. If you only have a shovel, you must be extra careful to give the plant a wide berth.

How to Lift Tubers Without Damage

Dahlia tubers are surprisingly fragile. They are connected to the main "crown" (the base of the stem) by narrow necks. If these necks break or crack, the tuber will not be able to sprout next year.

Step-by-Step Lifting

1. Clear the Mulch: Move any straw or wood chips away from the base of the plant so you can see exactly where the stems enter the ground.
2. The Wide Circle: Insert your garden fork into the soil about 12 inches away from the main stem. Prying too close to the center is the fastest way to snap a tuber.
3. Circle the Plant: Push the fork deep into the ground and gently pry upward. Move around the plant in a circle, loosening the soil from all sides.
4. Lift Gently: Once the soil is loose, use the fork to lift the entire clump from underneath. Use your hands to support the weight of the clump from below rather than pulling on the stems.
5. Shake Off Excess Soil: Gently shake the clump to remove large chunks of dirt. Do not bang the tubers against the ground or a tool, as this can cause bruising or breakage.

What to do next:

• Clear a workspace in a garage, shed, or basement.
• Gather your garden fork and labeling supplies.
• Check the weather for a clear day to work outside.

Cleaning and Drying the Tubers

Once the clumps are out of the ground, they need to be cleaned. There are two schools of thought on cleaning: the "wash" method and the "brush" method.

To Wash or Not to Wash?

Washing the tubers with a gentle stream from a garden hose makes it much easier to see the "eyes" and identify any rot or insect damage. However, washing adds a lot of moisture that must be dried out before storage. If you have heavy clay soil, washing is often necessary. If you have light, sandy soil, you can often just let the dirt dry and brush it off with your hands or a soft brush.

If you choose to wash them, do so gently. Avoid high-pressure nozzles that could tear the skin. After washing, the tubers must be dried thoroughly to prevent mold.

The Curing Process

Curing is the process of allowing the tubers to dry out slightly before they are packed away. Place your cleaned clumps upside down (with the stems pointing toward the ground) on a tray, a piece of cardboard, or a mesh screen. Turning them upside down allows any moisture trapped inside the hollow stems to drain out.

Keep the tubers in a cool, dark, frost-free location with good air circulation for 1 to 3 days. They should feel dry to the touch, and the skin may look slightly wrinkled, but they should still feel firm like a fresh potato. Do not leave them in direct sunlight or in a drafty area for too long, as they can shrivel and die.

Identifying Healthy Tubers for Storage

Before packing them away, inspect each clump. Not every tuber is worth saving. Look for the "Three Essentials" of a viable dahlia tuber:

• The Body: The fat part of the tuber that holds the food.
• The Neck: The narrow part connecting the body to the crown.
• The Crown (and Eye): The area where the tuber meets the stem. This is where the "eye" (the growth bud) is located.

Removing Damaged Parts

If you see tubers that are mushy, smell foul, or look like they are covered in a white, fuzzy mold, cut them away with a clean, sharp knife. You should also trim off any "mother" tubers. The mother tuber is the original one you planted in the spring; it is often darker, wrinkled, and prone to rotting over the winter. Leaving it attached can sometimes cause the new, healthy tubers to rot as well.

A Note on Toxicity

It is important to remember that dahlia tubers can be toxic to dogs, cats, and horses if eaten. While you are working with them and throughout the storage period, ensure they are kept in a location where pets cannot reach them. If you suspect a pet has ingested part of a tuber, contact your veterinarian.

To Divide or Not to Divide

One of the most common questions we receive is whether to divide the dahlia clumps in the fall or wait until spring. Both methods work well, and the choice often depends on your available space and time.

Dividing in the Fall

The primary advantage of dividing in the fall is that the tubers take up much less space. Instead of storing a basketball-sized clump, you are storing individual tubers that can fit into a small box. Additionally, the tubers are softer and easier to cut in the autumn.

The downside is that it can be very difficult to see the "eyes" in the fall. If you cut a tuber and don't include an eye from the crown, that tuber will never grow.

Dividing in the Spring

Many gardeners prefer to store the entire clump whole. The clump structure helps protect the individual tubers from drying out too quickly. In the spring, the eyes will begin to swell and turn pink or white, making them very easy to see. This ensures that every piece you divide will actually grow into a plant. The only drawback is that whole clumps require much more storage media and larger containers.

Key Takeaway: If you are a beginner, we recommend storing the clumps whole and dividing them in the spring when the eyes are clearly visible.

Choosing the Right Storage Media

You cannot simply toss dahlia tubers onto a shelf and expect them to survive. They need a "goldilocks" environment: not too wet (which causes rot) and not too dry (which causes shriveling). Using a storage medium helps regulate this moisture.

Popular Storage Options

• Peat Moss: This is the most popular choice. It is naturally slightly acidic, which helps prevent fungal growth, and it holds a small amount of moisture without being "wet."
• Vermiculite: This mineral-based medium is excellent for moisture control. It is very clean and easy to handle.
• Wood Shavings or Sawdust: Pine or cedar shavings (the kind sold for animal bedding) are inexpensive and provide good insulation.
• Newspaper: Wrapping individual tubers or clumps in several layers of dry newspaper is an old-fashioned method that still works well for many gardeners.

Avoid using garden soil or potting mix with added fertilizer, as these can hold too much moisture and encourage rot or premature growth.

Ideal Storage Conditions

Where you put your tubers is just as important as how you pack them. The goal is to keep them dormant. If they get too warm, they will try to grow in the dark, wasting their energy. If they get too cold, the water inside the cells will freeze and destroy the tuber.

The Temperature Sweet Spot

The ideal temperature for storing dahlias is between 40°F and 50°F (4°C to 10°C). For most people, this means an unheated basement, a root cellar, or a crawl space. An attached garage can work, but you must be careful that the temperature doesn't drop below freezing during a cold snap.

Humidity and Airflow

Dahlias prefer a humidity level of around 70% to 80%. If your storage area is very dry (like a heated basement), you may need to check your tubers more often. While you want to limit airflow to prevent drying, you don't want to seal them in an airtight plastic bag. This traps gases and moisture, which leads to rot. Use cardboard boxes, plastic bins with the lids left slightly ajar, or paper bags.

Packing Your Tubers for the Winter

Once your tubers are cured and you have chosen your medium, it is time to pack.

1. Bottom Layer: Place about 2 inches of your chosen medium (peat moss, shavings, etc.) in the bottom of a box or bin.
2. Arrange the Tubers: Lay your clumps or individual tubers on top of the medium. Make sure they are not touching each other. If one tuber starts to rot, you don't want it to spread to the others.
3. Cover: Add more medium until the tubers are completely covered.
4. Repeat: If your container is deep, you can add another layer of tubers and medium.
5. Label the Box: Clearly mark the outside of the box with the varieties inside and the date you packed them.

The "Saran Wrap" Method

Some gardeners have success with How to Store Dahlia Tubers in Plastic Wrap. This method prevents moisture loss and stops rot from spreading. However, it requires the tubers to be perfectly dry before wrapping. If even a drop of water is trapped inside, the tuber will rot quickly. This is often considered an advanced technique.

What to do next:

• Select your storage containers (cardboard boxes work great).
• Purchase your storage medium (peat moss or wood shavings).
• Identify a cool, dark spot in your home that stays above freezing.

Winter Maintenance and Monitoring

Overwintering dahlias is not a "set it and forget it" task. We recommend checking your tubers once a month throughout the winter. This allows you to catch small problems before they ruin your entire collection.

What to Look For

• Signs of Rot: If you find a tuber that feels soft, mushy, or smells bad, remove it immediately and throw it away. Check the neighboring tubers for any signs of spread.
• Signs of Shriveling: If the tubers look very wrinkled and feel light or "hollow," they are drying out. Lightly mist the storage medium with a spray bottle of water. Do not soak it; you just want to add a hint of humidity back into the air.
• Early Sprouting: If you see white sprouts beginning to grow, your storage area is likely too warm. Try to move the boxes to a cooler spot to keep them dormant until spring.

Overwintering in the Ground (Zones 8-11)

If you live in a warm climate, you have the luxury of leaving your dahlias in the ground. However, "in the ground" doesn't mean "without care." The biggest threat to dahlias in warm zones isn't the cold; it's the winter rain. Dahlias in soggy soil will rot very quickly.

Protection in Place

If you choose to leave them in the ground, cut the stems back as usual. Cover the entire area with a 4- to 6-inch layer of mulch, such as wood chips or straw. Some gardeners also place a piece of plastic or an old tarp over the dahlia bed during the rainiest months to keep the soil relatively dry. In the spring, simply pull back the mulch to allow the sun to warm the soil and trigger new growth.

Bringing Dahlias Out of Storage

As spring approaches and the threat of a hard frost passes, you can begin to prepare your tubers for planting. This usually happens about 2 to 4 weeks before your last expected frost date.

Waking Them Up

Bring your boxes into a warmer area (around 60°F) to "wake them up." If you didn't divide them in the fall, now is the time to do it. Look for the eyes near the crown. Once you see small bumps or "pimples" appearing, you know the tuber is healthy and ready to grow.

At this stage, we often pot up our favorite varieties in containers and keep them in a sunny window or a greenhouse. This gives them a head start on the season, leading to earlier blooms in the summer. Just remember not to move them outdoors permanently until the soil is warm and there is no danger of frost.

Successful Storage Starts with Healthy Plants

The better you care for your dahlias during the summer, the better they will store in the winter. At Longfield Gardens, we have found that plants grown in well-draining soil with consistent moisture produce the sturdiest tubers. Avoid over-fertilizing with high-nitrogen products late in the season, as this can lead to "watery" tubers that don't store as well. Instead, focus on providing plenty of sunlight and a balanced fertilizer during the peak blooming months.

Gardening is a journey of observation and adjustment. Your local microclimate—the specific temperature and humidity of your basement or garage—will dictate which storage method works best for you. Don't be afraid to experiment with different media or containers to find your own perfect system.

"Storing dahlia tubers is like putting your garden to bed. With a little bit of preparation and a cool, dark place to rest, your favorite flowers will be ready to wake up and shine again next summer."

Conclusion

Keeping dahlias over the winter is a rewarding practice that allows you to enjoy your favorite flowers year after year. By waiting for the first frost, lifting the tubers gently, and providing a cool, stable environment, you can protect your investment and even expand your garden as your tuber clumps grow. Gardening is meant to be an enjoyable and accessible hobby, and mastering dahlia storage is a simple skill that pays dividends in beautiful, colorful blooms.

• Wait for a killing frost to signal the start of dormancy.
• Use a garden fork to lift tubers carefully, avoiding the narrow necks.
• Store tubers in a cool (40–50°F), dark place using peat moss or wood shavings.
• Check your tubers monthly to ensure they are neither rotting nor shriveling.

We invite you to explore our selection of dahlias and other summer-blooming bulbs at Longfield Gardens to start building your dream garden today.

FAQ

Can I store dahlias in a refrigerator?

You can store dahlia tubers in a refrigerator if you have the space, provided the temperature stays between 40°F and 45°F. However, you must avoid putting them in the same refrigerator as ripening fruit (like apples), as the ethylene gas produced by the fruit can damage or kill the tubers. It is also important to ensure the refrigerator is not so cold that it causes the tubers to freeze.

What happens if I don't dig up my dahlias?

In USDA zones 7 and colder, the ground will freeze deep enough to reach the dahlia tubers. Since these tubers are mostly water, the freezing temperatures will cause the cells to burst, turning the tubers into a mushy, rotten mess by spring. If you want to keep your dahlias in these colder climates, you must lift them and store them indoors.

Do I need to treat my tubers with a fungicide before storage?

While not strictly necessary for most home gardeners, some people choose to dust their tubers with sulfur powder or a cinnamon-based antifungal powder before packing them away. This can help prevent mold and rot if your storage conditions are less than ideal. The most important factor in preventing rot, however, is ensuring the tubers are dry and the storage medium isn't overly wet.

Why did my dahlia tubers shrivel up during the winter?

Shriveling happens when the storage environment is too dry or the tubers were left out to cure for too long. If the tuber loses too much moisture, it will no longer have the energy needed to sprout in the spring. To prevent this, check your tubers monthly and lightly mist the storage medium with water if you notice the skins becoming excessively wrinkled or the tubers feeling light.