How Do I Overwinter Dahlia Tubers?

Table of Contents

1. Introduction
2. Understanding Dahlia Hardiness
3. Timing Your Harvest
4. Preparing the Plants for Digging
5. The Proper Way to Lift Tubers
6. Cleaning and Curing
7. Choosing Your Storage Container
8. Selecting a Storage Medium
9. The Ideal Storage Environment
10. Mid-Winter Maintenance
11. Overwintering in the Ground
12. Overwintering Dahlias in Containers
13. Common Myths About Overwintering
14. Troubleshooting Storage Issues
15. Looking Forward to Spring
16. Conclusion
17. FAQ

Introduction

Few things in the garden are as rewarding as the first dahlia bloom of the season. These spectacular dahlias provide a wealth of color and texture that lasts from midsummer right up until the first frost. Because they offer such an incredible return on investment, many gardeners want to keep their favorite varieties from year to year. At Longfield Gardens, we want to make sure you feel confident in preserving your collection so your garden stays vibrant season after season.

The process of saving your tubers through the winter is known as overwintering. While it might sound technical, it is a straightforward task that any gardener can master with a little bit of preparation. By following a few simple steps, you can protect these tender perennials from the cold and set them up for even more impressive growth the following spring.

This guide will walk you through the entire process, from the first autumn frost to the moment you tuck your tubers away for their winter nap. Whether you are a beginner or a seasoned grower, learning these techniques will help you maintain a beautiful and sustainable garden.

Understanding Dahlia Hardiness

Dahlias are native to the warm mountain regions of Mexico and Central America. Because of their tropical heritage, they are naturally adapted to climates where the ground never freezes. In the United States, dahlias are only considered hardy in USDA zones 8 through 11. In these warmer regions, the soil stays warm enough to protect the tubers through the winter months with minimal effort.

If you live in USDA zones 3 through 7, the winter temperatures frequently drop below freezing. Since dahlia tubers have a high water content, they will freeze and turn to mush if left in the ground during a cold winter. For most American gardeners, this means the tubers must be "lifted" or dug up and moved to a frost-free storage area.

Even if you live in a borderline zone like zone 7 or 8, you may still choose to dig up your tubers. Lifting them allows you to inspect the health of the root system, divide the clumps to create more plants, and protect them from winter rot caused by heavy rain or snow. Knowing your zone is the first step in deciding which overwintering path is right for your garden, and our hardiness zone map can help.

Timing Your Harvest

Success starts with timing. It is tempting to dig up your dahlias as soon as the weather turns chilly, but the plants actually benefit from staying in the ground as long as possible. As the days grow shorter in autumn, dahlias begin to store energy in their tubers. This energy acts as a fuel tank for the next year’s growth.

The best time to start the process is after the first "killing frost." This is the frost that turns the green foliage brown or black. While the top of the plant looks finished, the tubers underground are perfectly safe. Waiting for this frost signals to the plant that it is time to go dormant.

Many experienced gardeners wait about a week or two after the first frost before they start digging. This brief waiting period allows the "eyes"—the small bumps where next year’s stems will grow—to become more visible. It also helps the skin of the tuber toughen up, which makes them more resistant to rot and damage during storage. If your local forecast predicts a deep, ground-freezing freeze, however, you should move forward with digging to ensure the tubers stay protected.

Preparing the Plants for Digging

Before you bring out the garden fork, there is a little bit of housekeeping to do. Start by removing any labels or stakes that you used during the summer. If you have multiple varieties, it is vital to label each plant before you cut the stems. Once the foliage is gone and the tubers are out of the ground, it is nearly impossible to tell a Cafe au Lait from a pile of unlabeled clumps.

The same is true of Thomas Edison when the tags are missing. Use a permanent marker to write the variety name on a plastic garden tag or even directly on the tuber later. Some gardeners use surveyor's tape tied loosely around the base of the stem. Once your labels are secure, cut the main stems back to about three to five inches above the soil line.

Cutting the stems makes the plant much easier to handle. Dahlia stems are hollow, so they can sometimes collect water. By leaving a few inches of stem, you have a "handle" to hold onto while digging, and you also protect the crown—the area where the tubers meet the stem—from accidental damage.

Key Takeaway: Always label your dahlias before cutting them back. Once the flowers and leaves are gone, the tubers look identical, and labeling ensures you know exactly what you are planting next spring.

The Proper Way to Lift Tubers

Lifting dahlia tubers requires a gentle touch. Because the tubers are brittle and full of moisture, they can snap or puncture easily. A punctured tuber is more likely to develop rot during the winter months. Instead of a narrow shovel, we recommend using a garden digging fork. The tines of a fork allow you to lift the soil without the same risk of slicing through a tuber.

Start by digging a circle around the plant. You should stay at least 12 inches away from the center stem to avoid hitting the root clump. Most dahlia clumps grow outward as well as downward. Gently loosen the soil all the way around the plant by prying the fork upward.

Once the soil is loose, reach under the clump with your fork and lift it slowly. If you feel resistance, stop and loosen the soil a bit more. You want the entire root ball to come up as one piece. Once the clump is out of the ground, gently shake off the excess soil. Do not bang the tubers against the ground or a hard surface, as this can cause the necks of the tubers to crack.

Cleaning and Curing

Once your tubers are out of the garden, they need a little bit of cleaning and a short rest before they go into storage. For a closer look at tuber structure, see our Dahlia Tubers: What You Need to Know.

There are two main schools of thought regarding cleaning: washing them with a hose or simply brushing off the dry soil.

If your soil is heavy clay, washing the tubers with a gentle stream of water can help you see the health of the root system and look for any signs of pests or disease. If you have light, sandy soil, you can often just let the clumps dry for a few hours and then brush the dirt away with your hands. Both methods work well, so choose the one that fits your garden conditions.

After cleaning, the tubers need to "cure." This means letting them air dry in a protected area for one to three days. A garage, a shed, or a basement is a perfect spot. Avoid placing them in direct sunlight or in an area where they might freeze. Curing allows the outer skin to dry and prevents excess moisture from being trapped in your storage containers, which is the primary cause of winter rot.

What to Look For During Inspection

While cleaning your tubers, keep an eye out for these three things:

• Broken Necks: If a tuber is hanging by a thin, broken thread of skin, it won't be able to grow next year. It is best to remove these.
• Soft Spots: Any part of the tuber that feels mushy or smells bad should be trimmed away with a clean, sharp knife.
• Mother Tubers: The original tuber you planted in the spring can sometimes start to decompose by autumn. If it looks dark and shriveled compared to the new, plump tubers, you can carefully remove it.

Choosing Your Storage Container

The goal of winter storage is to keep the tubers dormant, cool, and just moist enough that they don't shrivel up like raisins. There are several ways to pack your tubers, and the right choice often depends on the humidity levels in your home.

Cardboard Boxes or Plastic Bins

Cardboard boxes are a classic choice because they allow for some air exchange. This is a great option if you live in a humid climate. If your home is very dry, like many modern houses with central heating, plastic storage bins might be a better choice. If you use plastic, leave the lid slightly ajar or drill a few small holes in the sides to prevent condensation from building up.

Paper Bags

For smaller collections, individual paper bags work beautifully. You can put one variety per bag, which makes organization very easy. The paper protects the tubers while still allowing them to breathe. These bags can then be tucked into a larger crate or box for the winter.

The Plastic Wrap Method

Some gardeners have success by wrapping individual, clean tubers tightly in plastic kitchen wrap. This "Saran wrap method" relies on the tuber's own moisture to keep it plump. While this can save space, it requires the tubers to be perfectly clean and dry before wrapping to avoid trapping bacteria.

Selecting a Storage Medium

You rarely want to store dahlia tubers "naked" in a box. Using a packing material, or storage medium, helps regulate moisture and provides insulation. There are several common materials that work well, and most are inexpensive and easy to find.

• Peat Moss: This is one of the most popular choices. It is lightweight and has natural anti-fungal properties. It should be used slightly damp—not wet. If you squeeze a handful, it should feel like a wrung-out sponge.
• Vermiculite: This mineral is excellent for moisture control. It can absorb excess water but also release it if the tubers get too dry. It is a very clean option that many professional growers prefer.
• Pine Shavings: Often sold as animal bedding, these are inexpensive and provide great airflow. They don't hold as much moisture as peat moss, so they are best for naturally humid storage areas.
• Potting Soil: If you have extra bags of dry potting soil, you can use that to bury your tubers. Just make sure the soil is fresh and hasn't been used for other plants previously.

What to do next:

1. Select a storage container (box, bin, or bag).
2. Fill the bottom with 2-3 inches of your chosen medium.
3. Lay your tubers or clumps in a single layer, making sure they aren't touching.
4. Cover them with more medium until they are fully submerged.
5. Label the outside of the container with the date and variety names.

The Ideal Storage Environment

Location is the most critical factor in overwintering success. Dahlia tubers need a "Goldilocks" environment: not too hot, not too cold, and not too dry.

The ideal temperature for storage is between 40°F and 50°F. If the temperature stays consistently above 50°F, the tubers may think it is spring and start to sprout prematurely. If the temperature drops below 32°F, the water inside the tubers will freeze, causing the cells to burst and the plant to die.

Common successful storage locations include:

• An unheated basement or crawlspace.
• A cool closet in a mudroom.
• An insulated garage (as long as it doesn't freeze).
• A root cellar.

Humidity also plays a role. Most tubers prefer a humidity level of around 70% to 80%. If your storage area is very dry, you may need to check your tubers more frequently to ensure they aren't shriveling.

Mid-Winter Maintenance

Overwintering is not a "set it and forget it" task. We recommend checking on your tubers about once a month. For more season-long care tips, see our 8 Tips for Growing Better Dahlias.

When you open your boxes, look for two things: rot and shriveling. If you see a tuber that has become soft or fuzzy with mold, remove it immediately. Mold can spread quickly from one tuber to another, so catching it early is key. If the mold is only on a small tip, you can cut that part off and dust the cut with cinnamon, which acts as a natural fungicide.

If the tubers look wrinkled or feel light and hollow, they are getting too dry. You can fix this by lightly misting the storage medium with a spray bottle filled with water. You don't want to soak the medium; just a light misting will provide enough humidity for the tubers to rehydrate.

Overwintering in the Ground

If you are lucky enough to live in USDA zones 8 through 11, you can often leave your dahlias right where they grew. This is a huge time-saver and allows the plants to establish very deep, robust root systems.

To overwinter in the ground, start by cutting the stems back to about three inches after the first frost. Cover the entire area with a thick layer of mulch. Six inches of straw, wood chips, or shredded leaves will act as a blanket, keeping the soil temperature stable.

The biggest risk for in-ground dahlias is not the cold, but the wet. In areas with very rainy winters, tubers can rot in soggy soil. If your garden has poor drainage, you might consider covering the mulched area with a piece of plastic or a tarp to shed the excess rain. In the spring, simply pull back the mulch once the threat of frost has passed to let the new shoots emerge.

Overwintering Dahlias in Containers

If you grow your dahlias in large pots, you don't necessarily have to dig them up. You can store the entire container. Once the foliage has died back, cut the stems down and move the pot to a cool, dark, frost-free location like a basement or garage.

Do not water the pot over the winter. You want the soil to stay dry so the tubers stay dormant. In early spring, you can move the pot back into the sun, give it a good drink of water, and watch the new growth begin. This is an excellent option for gardeners with limited space or for those who only grow a few favorite varieties.

Common Myths About Overwintering

There is a lot of advice online about dahlias, and some of it can be confusing for beginners. One common myth is that you must wash your tubers with a bleach solution. While some growers do this to kill bacteria, it isn't necessary for the home gardener. As long as your tubers are cured and stored in a clean medium, they should stay healthy.

Another myth is that you have to divide your tubers in the fall. While fall is a great time to divide if you are short on storage space, many gardeners prefer to wait until spring. In the spring, the "eyes" are much easier to see, which makes the dividing process much simpler for beginners. Storing the clumps whole is perfectly fine and often protects the individual tubers from drying out.

Troubleshooting Storage Issues

If you find that your tubers aren't making it through the winter, don't be discouraged. Gardening is a learning process, and every home environment is different. If your tubers are consistently rotting, try using a more breathable storage medium like pine shavings or increase the ventilation in your boxes.

If your tubers are shriveling despite your best efforts, your storage area may be too warm or too dry. Moving them to a lower shelf (where it is cooler) or using a plastic bin instead of a cardboard box can help retain the necessary moisture. Remember that even professional growers expect a small amount of loss each year. Success with 80% to 90% of your tubers is a fantastic result.

Looking Forward to Spring

As the winter begins to fade and the first signs of spring appear, your dahlias will start to wake up. Around four to six weeks before your last expected frost, you can bring your storage containers into a warmer room to encourage the eyes to sprout. For a spring refresher, see our How to Plant Dahlias.

This is the perfect time to divide your clumps if you haven't already. Each division just needs one healthy tuber with a visible eye and a solid neck. By overwintering your tubers, you are not just saving money; you are often increasing your garden's bounty. That single tuber you planted last year may have turned into a clump of five or ten new tubers, allowing you to fill even more of your yard with beautiful blooms.

At Longfield Gardens, we believe that gardening should be an enjoyable journey of discovery. Saving your dahlias is a wonderful way to connect with the life cycle of your plants and ensure that your garden remains a source of joy year after year.

Conclusion

Overwintering dahlia tubers is a simple and satisfying way to preserve your favorite flowers. By waiting for the first frost, digging carefully with a garden fork, and providing a cool, stable storage environment, you can enjoy the same beautiful blooms season after season. While it requires a bit of effort in the autumn, the reward of seeing those familiar colors return to your garden in the summer is well worth the work.

• Wait for a killing frost to signal dormancy.
• Label every variety before you cut the stems.
• Cure tubers for a few days before packing them away.
• Check your storage boxes monthly for rot or shriveling.

If you are ready to expand your collection or want to try new colors, we invite you to browse our dahlia tubers. We stand behind the quality of our plants and are here to support your gardening success every step of the way.

"The secret to a beautiful dahlia garden isn't just in the planting—it's in the care we provide during their quiet winter rest."

To browse even more dahlia options, visit our Dahlia Collections.

For broader spring shopping, explore our Spring-Planted Bulb Collections.

For shipping details and timing, visit our Shipping Information.

FAQ

Can I leave my dahlia tubers in the ground if I live in Zone 7?

In Zone 7, dahlias can sometimes survive the winter if the soil has excellent drainage and you apply a very thick layer of mulch. However, it is a bit of a gamble. If you have a variety you absolutely love and don't want to lose, we recommend digging it up and storing it indoors just to be safe.

Do I need to wash the dirt off the tubers before storing them?

Washing is a matter of personal preference. It can help you see the "eyes" and check for damage more easily, but it also adds moisture that must be dried off before storage. Many gardeners find success simply by brushing off the loose soil after the tubers have dried for a few hours.

What should I do if my tubers look shriveled in January?

If your tubers look wrinkled, they are losing too much moisture. Use a spray bottle to lightly mist the storage medium (like peat moss or shavings) with water. This increases the local humidity and helps the tubers stay plump without making them so wet that they begin to rot.

When is the best time to divide my dahlia clumps?

You can divide them in either fall or spring. Many beginners find it much easier to divide in the spring because the "eyes" (growth buds) begin to swell and turn pink, making them very easy to identify. If you are short on storage space, however, dividing in the fall allows you to fit more tubers into a smaller container. For more on dahlia care throughout the season, see our All About Dahlias.