Introduction
There is nothing quite like the feeling of watching your first dahlia of the season unfurl its petals. Whether it is a dinnerplate variety the size of a frisbee or a delicate pompon dahlia Jan van Schaffelaar in a vibrant shade of sunset orange, these flowers are the undeniable stars of the summer garden. At Longfield Gardens, we believe dahlia collections are one of the most rewarding plants you can grow, offering an incredible return on investment with armloads of blooms for months on end.
As the autumn air turns crisp and the garden begins to wind down, many gardeners find themselves asking a very important question: do dahlia bulbs need to be dug up? The answer is one of the most common points of confusion for beginners, but it is actually quite straightforward once you understand how these plants interact with your local climate. This guide is designed to help you determine the best winter plan for your dahlias so you can enjoy their spectacular beauty year after year.
Whether you choose to lift your tubers for indoor storage or try your luck leaving them in the ground, the goal is always the same: keeping the "heart" of the plant safe until spring returns. By following a few simple steps, you can ensure your dahlia collection stays healthy, vigorous, and ready to perform.
Understanding Your Garden’s Climate
The primary factor that determines whether you must dig up your dahlia tubers is your USDA plant hardiness zone. Dahlias are native to the high plains of Mexico and Central America, where they enjoy warm days and cool, frost-free nights. Because they evolved in a climate that never experiences a deep ground freeze, their tubers—the starchy, potato-like roots that store the plant's energy—are not naturally equipped to survive harsh northern winters.
In the United States, we use hardiness zones to understand which plants can survive the winter in a specific location. For dahlias, the "magic number" is generally Zone 8. If you live in Zone 8, 9, 10, or 11, you are in a region where the ground rarely freezes deep enough to damage the tubers. In these warmer climates, you can often leave your dahlias in the ground year-round with just a little extra mulch for protection.
However, if you live in Zone 7 or colder, the winter temperatures will eventually penetrate the soil. When the water inside a dahlia tuber freezes, it expands, causing the cell walls to burst. Once the ground thaws, the tuber turns into a soft, mushy mess that cannot grow. For gardeners in these regions, lifting and storing the tubers indoors is the most reliable way to keep the plants alive.
Key Takeaway To decide if you need to dig, check your USDA Plant Hardiness Zone Map. Gardeners in Zone 7 and colder should always dig their dahlias to ensure they survive the winter, while those in Zone 8 and warmer can often leave them in the ground.
The Benefits of Digging Up Dahlias
Even if you live in a region where dahlias might survive the winter in the ground, there are several excellent reasons to dig them up anyway. Lifting your tubers is not just about survival; it is also about the long-term health and productivity of your garden.
Preventing Rot in Wet Soil
While freezing is the biggest threat to dahlias, excessive moisture is a close second. Dahlias prefer to stay relatively dry during their dormant period. If your winter involves frequent rain or heavy, poorly draining clay soil, the tubers are highly susceptible to rot. By lifting them and storing them in a controlled environment, you remove the risk of losing your favorite varieties to soggy soil.
Controlling the "Clump" Size
Dahlias are incredibly productive. A single tuber planted in the spring will grow into a large "clump" of multiple tubers by October. If you leave these clumps in the ground for several years, they can become overcrowded. Overcrowded dahlias often produce smaller flowers and thinner stems because the plants are competing with themselves for nutrients and space. Digging them up allows you to divide the clumps, which keeps the plants vigorous.
Increasing Your Collection for Free
One of the most exciting parts of dahlia gardening is that one plant can become five or ten plants in just a single season. When you dig up a clump, you can separate the individual tubers. Each tuber that has a "neck" and an "eye" (the small bud where next year's growth begins) can be planted as its own individual plant next spring. This is a wonderful way to expand your garden or share your favorite varieties with friends and neighbors.
Rearranging Your Garden Design
Gardening is a creative process that evolves every year. If you leave your dahlias in the ground, you are locked into that specific layout for the following season. By digging them up, you give yourself a blank slate. You can move the tall varieties to the back of the border or try a new color palette with the Dahlia Dinnerplate Cloud Nine Collection in your cutting garden.
When Is the Right Time to Dig?
Timing is everything when it comes to lifting dahlias. If you dig too early, the tubers may not have stored enough energy to last through the winter. If you wait too long, you risk a deep freeze that could damage the tubers before you get to them.
The best signal to watch for is the first frost. Most gardeners wait until a "killing frost" has turned the dahlia foliage from vibrant green to a dark, blackened brown. This frost tells the plant that the growing season is officially over.
Once the foliage has died back, it is common practice to wait about 7 to 10 days before digging. During this week of "curing" in the ground, the tubers go into a deep dormancy and their skins begin to toughen up. This thicker skin helps prevent the tubers from shriveling or drying out too much while they are in winter storage.
If you live in an area that does not get a frost until very late in the year, or if you simply want to get a head start on your fall chores, you can dig them up around mid-October. As long as the plants have had at least 120 days of growth, the tubers should be mature enough to store successfully.
What to Do Next
- Watch the weather forecast for the first light frost.
- Once the leaves turn black, cut the stems down to about 4 to 6 inches above the ground.
- Mark each plant with a tag or waterproof marker so you remember which variety is which.
- Wait one week, then prepare your tools for digging.
Step-by-Step: How to Dig Your Dahlias
Lifting dahlias is a satisfying task that connects you to the lifecycle of your garden. You don't need fancy equipment—a basic garden fork and a pair of loppers are usually all it takes.
Step 1: Cut Back the Foliage
Before you start digging, clear away the top growth. Use garden pruners or loppers to cut the main stems down, leaving a few inches of "handle" sticking out of the ground. This handle makes the clump much easier to move and helps you keep track of where the center of the plant is located. Dispose of the foliage in your compost pile, provided the plants were healthy and free of disease.
Step 2: Loosen the Soil
The most important rule when digging dahlias is to give the tubers plenty of space. Dahlia tubers can grow surprisingly far from the main stem. If you thrust a shovel directly next to the stem, you are likely to slice right through the tubers.
Instead, start digging about 12 inches away from the stem on all sides. Use a garden fork if possible, as the tines are less likely to cause major damage than a solid shovel blade. Gently pry the soil upward, working your way around the entire plant until the clump feels loose.
Step 3: Lift with Care
Once the soil is loosened, place your fork deep under the center of the clump and lift it gently. Try to support the weight of the clump from underneath rather than pulling on the stems. The "neck"—the thin part where the tuber attaches to the main stem—is very fragile. If a tuber breaks off at the neck, it usually won't be able to grow next year because it lacks an eye. For a deeper explanation of tuber anatomy, see Dahlia Tubers: What You Need to Know.
Step 4: Clean the Tubers
Gently shake or brush off the large clumps of soil. Some gardeners prefer to wash their tubers with a garden hose to see the "eyes" more clearly, while others prefer to leave a little dirt on them to act as a natural insulator. If you do wash them, be sure to let them dry completely in a shaded, frost-free area for a day or two before packing them away. Moisture trapped against the skin is the primary cause of mold in storage.
Winterizing Dahlias in the Ground
If you are lucky enough to live in Zone 8 or warmer, or if you simply want to experiment with leaving a few tubers in the ground in Zone 7, you can take steps to increase their chances of survival. This process is often called "overwintering" or "winterizing," and How to Overwinter Dahlias covers the details.
The goal is to keep the soil temperature as stable as possible. A sudden cold snap can freeze the top few inches of soil, but a thick layer of insulation can keep the tubers cozy underneath.
The Power of Mulch
After you cut the stems down to ground level, cover the area with a generous layer of mulch. Use materials like wood chips, straw, shredded leaves, or bark. A layer that is 4 to 6 inches deep is usually sufficient. This mulch acts like a blanket, trapping the earth's natural heat and preventing the frost from reaching the tubers.
Improving Drainage
If you know your garden tends to stay wet in the winter, leaving dahlias in the ground is a riskier move. You can help by mounding the soil slightly over the plant before mulching so that rainwater runs off to the sides rather than pooling directly over the tubers. Some gardeners even place a piece of plastic or an inverted bucket over the spot during particularly rainy months to keep the "crown" of the plant dry.
Spring Cleanup
If you leave your dahlias in the ground, keep the mulch in place until the danger of frost has passed in the spring. Once the weather warms up, pull the mulch back to allow the sun to warm the soil. You will be rewarded when you see those first sturdy green shoots poking through the earth, often weeks earlier than dahlias planted from storage.
Storing Your Tubers for the Winter
If you have decided to dig your dahlias, the next step is finding them a comfortable place to sleep until spring. Successful storage depends on three main things: temperature, humidity, and the storage medium.
Finding the Right Temperature
Dahlias like to stay cool but not cold. The ideal temperature range is between 40°F and 50°F. An unheated basement, a crawl space, or a cool closet in a garage that stays above freezing are all excellent options. If the temperature stays too warm (above 60°F), the tubers may start to sprout too early or shrivel up. If it drops below 35°F, you risk them freezing.
Choosing a Storage Medium
To prevent the tubers from drying out completely, it is best to pack them in a material that holds a tiny bit of moisture but still allows the tubers to "breathe." Popular choices include:
- Vermiculite: A lightweight mineral that provides excellent insulation and moisture control.
- Peat Moss: A classic choice that is easy to find, though it can be a bit dusty.
- Wood Shavings: Often sold as pet bedding, these provide good airflow.
- Newspaper: Wrapping tubers individually in sheets of newspaper is a simple, low-cost method.
The Storage Container
Place your tubers and storage medium in a container that allows for some air circulation. Plastic bins with a few holes drilled in the sides, cardboard boxes, or even paper bags work well. Avoid airtight plastic bags, as these will trap moisture and lead to rot.
Key Takeaway Check on your stored tubers once a month during the winter. If they look shriveled, mist the packing medium slightly with water. If you see any soft spots or mold, remove the affected tuber immediately to prevent the problem from spreading.
Why Some Gardeners Choose Not to Dig
Despite all the benefits of digging, it is perfectly okay to decide that lifting dahlias isn't for you. Some gardeners choose to treat dahlias as "annuals," much like petunias or zinnias. They enjoy the incredible blooms all summer long and then let the plants fade away when winter arrives.
Because we offer a wide variety of high-quality tubers at Longfield Gardens, many of our customers enjoy the excitement of picking out the Dahlia Dinnerplate Daybreak Collection every spring. Treating dahlias as annuals allows you to experiment with different garden designs every year without the commitment of winter storage.
There is no "wrong" way to enjoy dahlias. Whether you preserve your favorites for decades or start fresh each spring, the joy they bring to the garden remains the same.
Troubleshooting Common Winter Issues
Even with the best intentions, things can sometimes go sideways during the winter. Understanding what to look for can help you save your collection before it's too late.
Tubers Turning Soft
If you press on a tuber and it feels like a soft sponge, it has likely succumbed to rot. This is usually caused by too much moisture during storage or the tuber being damaged during the digging process. If you find a soft tuber, discard it immediately. To prevent this next time, ensure your tubers are completely dry before packing and increase the airflow in your storage container.
Shriveled, "Mummified" Tubers
It is normal for tubers to lose a little bit of their plumpness over the winter, but they should not look like dry raisins. If they are extremely shriveled, your storage area is likely too dry. You can try to revive them by soaking them in room-temperature water for a few hours before planting in the spring. Moving forward, try using a slightly more moisture-retentive packing medium like vermiculite.
Early Sprouting
Sometimes, a warm spell in February or March can trick your dahlias into thinking spring has arrived early. You might see small white or pale green sprouts appearing on the crown. If this happens, try to move the tubers to a slightly cooler spot to slow them down. You don't need to break the sprouts off; just be very careful not to snap them when it is finally time to plant.
Preparing for Spring Planting
The effort you put into digging and storing your dahlias pays off the moment the soil warms up in the spring. Usually, this is around the same time you would plant your tomatoes—when the danger of frost has passed and the soil temperature is consistently around 60°F.
If you stored your tubers in clumps, spring is a great time to divide them. The "eyes" are much easier to see in the spring because they will be starting to swell and turn pink or green. Dividing in the spring ensures that every piece you plant is healthy and ready to grow.
Before planting, give your tubers a quick inspection. A healthy tuber should feel firm, like a fresh potato. If it has a visible eye or a small sprout, you are off to a perfect start. How to Plant Dahlias is a helpful refresher for spacing, depth, and timing. Plant them about 4 to 6 inches deep in a sunny spot with well-draining soil, and get ready for another spectacular season of color.
Conclusion
Deciding whether to dig up your dahlia bulbs is a choice that depends entirely on your location and how you like to garden. For those in colder climates, lifting the tubers is a rewarding ritual that ensures your favorite varieties return year after year. For gardeners in warmer zones, a thick layer of mulch is often all that's needed to keep the "magic" alive through the winter months.
At Longfield Gardens, we want every gardener to feel confident in their ability to grow these stunning flowers and in our 100% Quality Guarantee. Whether you are digging, dividing, or simply planning your next color palette with the Dahlia Dinnerplate Berry Spritz Collection, remember that gardening is a journey of discovery. There is no greater satisfaction than seeing those first green shoots emerge, knowing that a summer full of beauty is just around the corner.
- Determine your zone: Dig if you are in Zone 7 or colder.
- Wait for frost: Let the plants go dormant before lifting.
- Store cool and dry: Aim for 40-50°F in a breathable container.
- Be patient: Spring planting brings the reward of a whole new season of blooms.
The secret to a beautiful dahlia garden isn't just in the planting; it's in the care we provide during the quiet months of winter. By protecting the tubers today, you are ensuring a more vibrant and colorful tomorrow.
FAQ
Can I leave dahlias in the ground in Zone 7?
It is possible but risky. In Zone 7, the ground can freeze deep enough to kill dahlia tubers during an especially cold winter. If you choose to leave them, you must apply a very thick layer of mulch (at least 6 inches) and ensure the soil has excellent drainage to prevent rot. Many gardeners in this zone prefer to dig them up just to be safe.
Do I need to wash the dirt off before storing dahlias?
Washing is optional. Some gardeners like to wash tubers so they can easily see the "eyes" and check for damage or disease. Others find that leaving a light coating of soil helps protect the tubers from drying out. If you do wash them, the most important thing is to ensure they are 100% dry before you put them into storage.
What happens if I don't dig up my dahlias in a cold climate?
In regions where the ground freezes solid (Zone 6 and colder), dahlias left in the ground will almost certainly die. The water inside the tubers will freeze, causing them to rot once the ground thaws. In these areas, dahlias are treated as annuals unless the tubers are lifted and stored indoors for the winter.
Can I store dahlia tubers in the refrigerator?
While a refrigerator is cool, it is usually too cold and too dry for dahlia tubers. Most refrigerators are kept around 35-38°F, which is dangerously close to the freezing point for dahlias. Additionally, the low humidity in a fridge can cause the tubers to shrivel quickly. A cool basement or crawl space is a much better environment.
