Introduction
The end of the gardening season often brings a mix of nostalgia and excitement. While we say goodbye to the vibrant summer borders, we also look forward to the promise of next year’s growth. Dahlias are often the stars of this transition, blooming with incredible intensity right up until the first frost. These spectacular flowers, which we offer in a wide array of colors and shapes in our Dahlia Collections, are among the most rewarding plants you can grow.
However, because dahlias are native to the warm climates of Mexico and Central America, they aren't naturally equipped to handle freezing northern winters. This leads to one of the most common questions we receive: do you actually have to dig them up every single year? The answer isn't a simple yes or no; it depends on where you live, your soil conditions, and how much effort you want to put into your garden chores.
In this guide, we will explore when digging is a necessity and when you might be able to leave your tubers tucked into the soil. We’ll also cover the best practices for both methods so you can feel confident in your garden’s success. Whether you are a beginner or a seasoned grower, understanding how to manage your dahlia tubers is the key to enjoying their stunning blooms year after year.
The Role of USDA Hardiness Zones
The first step in deciding whether to dig is identifying your USDA hardiness zone. This map is the standard by which gardeners can determine which plants are likely to thrive at a specific location. Dahlias are generally considered hardy in zones 8 through 11. In these warmer regions, the ground rarely freezes deep enough to reach the tubers, allowing them to remain in the garden year-round with minimal protection.
If you live in zones 7 or colder, the situation changes. In these climates, the soil temperature can drop low enough to freeze the water inside the tuber. Since tubers are primarily composed of water and starch, freezing causes the cellular structure to burst, turning the tuber into a mushy, non-viable mess once it thaws. In these areas, digging and storing the tubers indoors is the traditional and most reliable way to ensure they return.
However, many gardeners in zone 7 find success by leaving their tubers in the ground if they provide extra protection. Microclimates—such as a sheltered bed against a south-facing brick wall—can sometimes keep the soil just warm enough to bridge the gap. While we recommend digging in zone 7 for guaranteed results, adventurous gardeners often enjoy experimenting with in-ground overwintering to save time.
Why Dahlias Might Not Survive the Ground
Temperature isn't the only factor at play when we talk about overwintering. Even in warmer zones where frost isn't a threat, moisture can be a significant enemy. Dahlias need "right plant, right place" conditions even when they are dormant. If your garden has heavy clay soil that stays saturated and cold throughout the winter, your tubers are at high risk of rotting.
Dahlias are susceptible to fungal and bacterial rot when they sit in cold, wet earth. This is why drainage is often the "quiet winner" in dahlia care. If your soil is sandy or well-drained, your tubers have a much better chance of survival than if they are sitting in a waterlogged low spot. If you find that your garden tends to hold water in the winter, digging them up is usually the safer choice, regardless of your temperature zone.
Key Takeaway: Soil moisture is just as important as temperature. If your winter ground is consistently wet and soggy, digging up your tubers is the best way to prevent rot and ensure a healthy start for the following spring.
How to Overwinter Dahlias in the Ground
If you live in zone 8 or above, or if you are in zone 7 and want to take the risk, leaving your dahlias in the ground can save you a significant amount of manual labor. Leaving them in place also allows the plant to form a larger, more established clump over several years, which can lead to more vigorous growth and a higher volume of flowers.
Prepare the Plants
Wait until the first light frost has blackened the foliage. This frost signals the plant to stop active growth and move its energy down into the tubers for dormancy. Once the stems have turned dark, cut them down to about 2 to 4 inches above the soil line. Some gardeners prefer to wait a week after the frost before cutting to allow every last bit of nutrients to return to the tuber.
Insulate the Soil
The goal of in-ground overwintering is to keep the soil temperature stable. You can achieve this by applying a thick layer of mulch over the top of the cut stems. We recommend using 6 to 12 inches of straw, shredded leaves, or wood chips. This "blanket" prevents the ground from fluctuating between freezing and thawing, which is often more damaging than a steady cold.
Manage Excess Moisture
In areas with very wet winters, you might consider covering your dahlia bed with a waterproof tarp after mulching. This prevents the soil from becoming saturated. If you go this route, be sure to remove the tarp in early spring as soon as the weather warms, or you may trap too much heat and cause the tubers to sprout prematurely or rot.
- Cut stems to 3 inches after the first frost.
- Apply 6–12 inches of dry mulch (straw or leaves).
- Ensure the area has excellent drainage.
- Mark the spot with a stake so you don't accidentally dig there in early spring.
The Benefits of Digging Your Tubers
While digging sounds like a chore, it offers several advantages that leaving them in the ground does not. For many of us, the process of lifting tubers is an exciting way to check on the "underground health" of our garden and prepare for an even bigger display next season.
Multiplication and Division
One of the most incredible things about dahlias is how they multiply. If you plant one single dahlia tuber in the spring, you will likely find a clump of five to ten tubers when you dig it up in the fall. By digging them up, you have the opportunity to divide these clumps. This means you can turn one plant into many, allowing you to fill more of your garden or share the extras with friends and neighbors.
Quality Control
Digging allows you to inspect your stock. You can see if any tubers have become diseased or if pests have been nibbling on them. It also gives you the chance to "reset" your garden layout. If a particular variety didn't look right in its current spot, digging it up makes it easy to move it elsewhere next year.
Protection from the Elements
Storing tubers indoors gives you total control over their environment. You don't have to worry about an unexpected polar vortex or a month of record-breaking rainfall. For rare or expensive varieties that we carry in our Dahlia Collections, digging provides the peace of mind that your investment is safe from the unpredictable nature of winter weather.
Step-by-Step: How to Dig and Store Dahlia Tubers
If you’ve decided that digging is the right path for your garden, following a simple, methodical process will yield the best results. You don't need fancy equipment; a few basic tools and a bit of patience are all it takes.
Wait for the Right Signal
Timing is everything. Do not dig your dahlias while they are still green and blooming. They need the late-season sun to build up the starches required for winter survival. Wait until a killing frost has turned the foliage brown or black. If a frost doesn't come by mid-November in your area, you can cut them back manually to force dormancy, but waiting for nature is usually best.
Lifting the Clump
Once the foliage is cut back, use a garden fork rather than a shovel. A fork is less likely to slice through the tubers. Start digging about 12 inches away from the main stem. This ensures you are outside the reach of the tuber clump. Gently pry upward from several sides to loosen the soil until the entire clump can be lifted easily.
Avoid pulling on the stems. The "neck" of the tuber—the thin part that connects the body to the crown—is very fragile. If the neck breaks, the tuber will not be able to grow next year because the "eye" (the growth point) is located on the crown.
Cleaning and Drying
Shake off as much loose soil as possible. Some gardeners prefer to wash their tubers with a gentle stream from a garden hose to remove all dirt, which makes it easier to spot the eyes and check for rot. Others prefer to keep the dirt on, much like storing potatoes. Both methods can work, but if you wash them, you must ensure they are completely dry before packing them away.
Let the cleaned tubers sit in a frost-free, shady area (like a garage or basement) for 1 to 3 days to "cure." This allows the skin to toughen up slightly, which helps prevent moisture loss during storage.
Packing for the Winter
The goal of storage is to keep the tubers dormant: not so dry that they shrivel, and not so wet that they rot. We find that the best way to achieve this is to pack them in a breathable medium.
- Select a container: Cardboard boxes, plastic bins with ventilation holes, or burlap bags all work well.
- Add a medium: Place a layer of slightly damp (not wet) vermiculite, peat moss, or sawdust in the bottom.
- Layer the tubers: Place the tubers in the container, making sure they aren't touching each other. Cover them with more of your chosen medium.
- Label everything: Use a permanent marker to write the variety name directly on the tuber or attach a tag. It is very easy to forget which is which by springtime!
Key Takeaway: Successful storage is a balance of humidity and temperature. Aim for a storage spot that stays between 40°F and 50°F. If the tubers get too warm, they will sprout; if they get too cold, they will freeze.
Common Storage Media Options
Choosing the right packing material can depend on what you have available and how much humidity your storage area naturally holds.
- Vermiculite: This is a popular choice because it holds onto a tiny bit of moisture while still allowing for air circulation. It is very clean and easy to handle.
- Peat Moss: A classic choice, peat moss is naturally anti-fungal. However, it can be dusty, so you might want to wear a mask when handling it.
- Wood Shavings/Sawdust: Often used for pet bedding, these are inexpensive and effective. Avoid shavings from treated lumber.
- Plastic Wrap: Some gardeners successfully wrap individual, cleaned tubers in plastic wrap. This "Saran wrap method" relies on the tuber's own moisture to stay plump. While it works for many, it requires the tubers to be perfectly clean and dry to avoid trapping rot-causing bacteria.
Monitoring Your Tubers Through Winter
Overwintering isn't a "set it and forget it" task. We recommend checking on your stored tubers once a month. This small effort allows you to catch issues before they ruin the whole batch.
If you notice a tuber feels soft or mushy, or if you see fuzzy mold growing, remove it immediately. Rot can spread quickly from one tuber to the next. If the tubers look shriveled and wrinkled like a raisin, they are losing too much moisture. Give the storage medium a very light misting with water—just enough to add a hint of humidity, not enough to make it wet.
If you see early sprouts in February or March, your storage area is likely too warm. Move the containers to a cooler spot to keep them dormant until it's time to plant.
Treating Dahlias as Annuals
It is perfectly okay to decide that digging and storing is not for you. Many busy gardeners choose to treat dahlias as annuals. In this scenario, you enjoy the spectacular blooms all summer long and then let the plants go once the frost hits.
This approach allows you to try completely new varieties and color schemes every year without the commitment of winter storage. Given the high volume of flowers a single dahlia provides over a season, many feel the cost of a new tuber each spring is a small price to pay for the joy they bring. At Longfield Gardens, we offer a wide selection each season, making it easy to refresh your garden with new dahlias.
When to Start Planting Again
Whether you left your tubers in the ground or stored them in the basement, the return of spring is the most exciting time. However, patience is key. "Timing beats tricks" when it comes to planting dahlias.
Do not be tempted to plant them as soon as the first warm day arrives. Dahlias need warm soil to thrive. Wait until the danger of frost has completely passed and the soil temperature reaches about 60°F. In many regions, this coincides with the time you would plant tomatoes or peppers.
If you left your tubers in the ground, this is when you should remove the heavy layer of mulch. Gently clear the area to allow the sun to warm the soil. You’ll soon see those first purple-green shoots poking through the earth, signaling the start of another glorious season.
Choosing the Right Tools
Having the right tools makes the job feel like a rewarding hobby rather than a difficult chore.
- Garden Fork: The broad tines are perfect for lifting large clumps without causing structural damage to the tubers.
- Pruning Shears: A sharp pair of bypass pruners will make quick work of the thick, hollow dahlia stems.
- Labels and Markers: Never underestimate the power of a good label. Garden-grade markers are best as they won't fade if they get a little damp.
- Storage Bins: Sturdy, stackable bins help keep your storage area organized.
Safety and Handling
While gardening is a safe and healthy activity, there are a few things to keep in mind when handling dahlia tubers.
- Toxicity: Dahlia tubers and foliage are considered mildly toxic to dogs and cats if ingested. They can cause skin irritation or stomach upset. If you have pets that like to dig or chew, keep your tubers stored in a secure location and monitor your pets in the garden.
- Cleanliness: If you are dividing your tubers, we recommend dipping your cutting tools in a solution of one part bleach to ten parts water between different plants. This prevents the spread of any potential viruses from one clump to another.
Conclusion
Deciding whether you have to dig up your dahlia tubers depends entirely on your local environment and your personal gardening style. If you live in a cold or very wet climate, digging and storing them is the most reliable way to preserve your favorite varieties. In warmer, well-drained areas, a thick layer of mulch is often all you need to keep them safe through the winter.
Gardening should always be an enjoyable and rewarding experience. Whether you choose the path of storage, in-ground protection, or treating your dahlias as annuals, you are set up for success as long as you focus on the basics of temperature and drainage.
- Check your USDA zone to determine the risk of freezing.
- Dig if your soil is heavy or stays wet during the winter.
- Store tubers in a cool, dark, and dry medium to keep them dormant.
- Monitor stored tubers monthly to prevent the spread of rot.
Digging up your dahlias is not just a chore; it is an opportunity to see the amazing way nature multiplies and prepares for the future. With just a little bit of care, those few tubers you plant today will become a lifetime of summer color.
For more information on selecting the perfect varieties for your garden, explore our planning guides and collection at Longfield Gardens. We are here to help you grow a garden you love, one season at a time.
FAQ
Can I leave my dahlias in the ground in Zone 7?
While Zone 7 is on the edge of dahlia hardiness, you can often leave them in the ground if you provide a very thick layer of mulch (6–12 inches) and ensure the soil has excellent drainage. However, since a particularly harsh winter can still freeze the ground deeply, digging them up remains the only way to guarantee their survival in this zone.
What happens if I don't dig up my dahlias in a cold climate?
In climates where the ground freezes (Zone 6 and colder), the water inside the dahlia tuber will freeze and expand, destroying the plant's tissue. Once the ground thaws in the spring, the tubers will rot and turn into mush, meaning the plant will not grow back.
How do I know if my stored tubers are still good in the spring?
Healthy tubers should feel firm to the touch, similar to a fresh potato. If a tuber is shriveled but still firm, it can often be revived by a quick soak in water before planting. If the tuber is mushy, smells foul, or crumbles in your hand, it has rotted and should be discarded.
Is it better to wash the tubers or leave the dirt on for storage?
Both methods have successful followers. Washing tubers makes it easier to inspect for disease and find the "eyes" for division, but they must be dried thoroughly for several days to prevent rot. Leaving the dirt on can provide a natural protective layer that helps maintain moisture, similar to how root vegetables are stored in a root cellar.
