Table of Contents
- Introduction
- Understanding Your Hardiness Zone
- The Impact of Soil and Drainage
- When You Can Leave Dahlias in the Ground
- When Digging Up Tubers is Necessary
- How to Dig and Lift Dahlia Tubers
- Curing and Storing Your Tubers
- To Divide or Not to Divide?
- Realistic Expectations for Overwintering
- Why Quality Matters from the Start
- Conclusion
- FAQ
Introduction
There is nothing quite like the late-summer magic of a dahlia garden. When those dinnerplate-sized blooms begin to open, showing off intricate petals in every color of the sunset, it feels like the ultimate reward for a season of care. At Longfield Gardens, we know that these spectacular dahlias are the highlight of the year for many home gardeners, and we want to help you enjoy them year after year.
One of the most common questions we receive as the weather turns crisp is whether those precious tubers can stay in the garden or if they must be brought indoors. This is a great question for anyone who wants to protect their investment and ensure a repeat performance next summer. Whether you are a beginner looking for an easy win or a seasoned gardener planning for next spring, understanding how dahlias interact with your local climate is the key to success.
This guide will help you determine if digging is necessary for your specific backyard conditions. We will cover how your hardiness zone and soil type influence this decision, and we will walk through the simple steps for both winterizing in the ground and lifting tubers for storage. By the end, you will have a clear plan for your dahlias that feels achievable and rewarding.
Key Takeaway: Determining whether to dig up your dahlia tubers depends primarily on your USDA hardiness zone and your soil’s drainage, but both paths can lead to a beautiful garden next season.
Understanding Your Hardiness Zone
The most important factor in deciding if you need to dig up dahlia tubers is your USDA hardiness zone. Dahlias are native to the warm, high-altitude regions of Mexico and Central America. Because they evolved in a climate with mild winters, they are not naturally equipped to survive deep, frozen ground.
In the United States, dahlias are generally considered hardy in zones 8 through 11. If you live in these warmer regions, your soil likely stays warm enough throughout the winter that the tubers will not freeze. In these areas, the tubers can often remain in the ground year-round with very little intervention.
For gardeners in zones 7 and colder, the ground typically freezes deep enough to damage or kill the tubers. If the water inside the tuber freezes, it expands and destroys the plant's cellular structure, leading to a mushy, non-viable clump in the spring. In these cooler zones, lifting the tubers is the standard practice to ensure they survive. However, even in zone 7, some gardeners find success leaving them in the ground if they provide a heavy layer of protection.
How to Check Your Zone
If you are unsure of your zone, you can find it easily by looking at a USDA Plant Hardiness Zone Map. This map is based on the average annual minimum winter temperature.
We use these zones to determine our shipping schedule, ensuring your plants arrive at the right time for planting in your specific area. Knowing your zone takes the guesswork out of many gardening decisions, including how to handle your dahlias in the fall.
The Role of Microclimates
Sometimes, your specific backyard might be slightly warmer than the official zone for your city. This is called a microclimate. For example, a flower bed located right against a south-facing brick wall often stays several degrees warmer than a bed in the middle of an open lawn. If your dahlias are planted in a sheltered spot near the foundation of your home, they may have a better chance of surviving a cold winter than those in an exposed field.
The Impact of Soil and Drainage
While temperature is the biggest factor, soil moisture is a close second. Dahlias are more likely to survive a cold winter in dry soil than in wet soil. When dahlia tubers are dormant, they do not take up much water. If they sit in cold, soggy earth for several months, they are highly susceptible to rot.
Well-Draining Soil
If your garden has sandy soil or a high amount of organic matter that allows water to move through quickly, your tubers have a higher chance of survival. In these conditions, even a colder-than-usual winter might not be a problem because the tubers stay relatively dry.
Heavy Clay Soil
If your garden has heavy clay soil that holds onto water, leaving dahlias in the ground is much riskier. Clay acts like a cold, wet sponge during the winter months. This constant moisture can cause the tubers to decay long before the spring sun arrives to wake them up. If you have heavy soil and live in a marginal zone like zone 7 or 8, we generally recommend digging up your tubers to keep them safe and dry indoors.
When You Can Leave Dahlias in the Ground
If you live in zone 8 or warmer, you can likely skip the digging and enjoy a bit of extra free time in the fall. Leaving the tubers in the ground allows them to form large, established clumps that often produce even more flowers the following year. However, "leaving them in the ground" doesn't mean ignoring them entirely.
Cutting Back the Foliage
Once the first frost hits, the beautiful green foliage will turn black and limp. This is your signal that the plant has gone dormant. Use a clean pair of garden snips to cut the stems down to about 2 to 4 inches above the soil line. This keeps the garden looking tidy and prevents the old, dead foliage from harboring pests or diseases over the winter.
Adding a Protective Mulch Layer
Even in warm zones, a sudden cold snap can be dangerous. We suggest applying a thick layer of mulch over the top of the cut stems. A 4- to 6-inch layer of straw, shredded leaves, or wood chips acts like a thermal blanket for the soil. This mulch keeps the soil temperature stable and prevents the ground from fluctuating between freezing and thawing, which is very stressful for the plants.
Protecting Against Excessive Rain
In regions with very wet winters, like the Pacific Northwest, the main threat to dahlias is often rain rather than cold. Some gardeners choose to cover their dahlia beds with a piece of plastic or a waterproof tarp during the wettest months. This keeps the soil underneath relatively dry and significantly reduces the risk of the tubers rotting.
What to Do Next:
- Identify your USDA hardiness zone to determine your baseline risk.
- Evaluate your soil drainage—if it's heavy clay, consider digging even in warmer zones.
- If leaving tubers in the ground, cut back dead foliage after the first frost.
- Apply a 4- to 6-inch layer of mulch to provide a winter "blanket."
When Digging Up Tubers is Necessary
For most of the country, especially in zones 3 through 7, digging up dahlia tubers is a necessary part of the gardening calendar. While it requires a bit of effort, the process is straightforward and can be very rewarding. It gives you the chance to see how much your plants have grown and ensures you won't have to buy new tubers every single spring.
The Benefit of Healthy Dormancy
Lifting the tubers allows you to control the environment. Instead of leaving them to the mercy of unpredictable winter weather, you can keep them in a cool, dark, and dry space. This "sleep" period is essential for the plant's lifecycle. When you replant them in the spring, they will be refreshed and ready to grow with vigor. For the spring planting step, How to Plant Dahlias will walk you through the process.
Trial and Error in Zone 7
If you live in zone 7, you are in a "borderline" area. Some years, a thick mulch layer is enough to keep dahlias alive through the winter. In other years, a particularly deep freeze might kill them.
Many gardeners in this zone choose to dig up their most precious or expensive varieties, like Cafe au Lait.
Others keep Labyrinth safe in storage while experimenting with leaving more common varieties in the ground.
This balanced approach helps you learn what works best in your specific microclimate.
How to Dig and Lift Dahlia Tubers
The best time to dig up your dahlias is about two weeks after the first "killing" frost. A light frost might just singe the leaves, but a killing frost will turn the entire plant black. Waiting these extra few days allows the plant to send one last burst of energy down into the tubers, which helps them stay healthy during their winter nap.
Step 1: Cut Back the Stalks
Start by cutting the stems down so only about 4 to 6 inches of the stalk remains above the ground. These remaining stems act as a handy "handle" while you are digging, but be careful not to pull on them too hard, as the "neck" where the tuber connects to the stem is quite fragile.
Step 2: Loosen the Soil
Using a garden fork or a shovel, begin digging in a circle about 12 inches away from the center of the plant. You want to avoid accidentally slicing through the tubers with your tools. Slowly work your way around the plant, gently prying the soil upward to loosen the root ball.
Step 3: Lift the Clump
Once the soil is loose, slide your shovel deep under the clump and lift it out of the ground. Dahlias can grow surprisingly large in a single season! A single tuber planted in May can turn into a clump the size of a basketball by October. Carefully shake off the excess soil so you can see what you are working with.
Step 4: Clean and Inspect
We recommend gently washing the remaining dirt off the tubers with a garden hose. For a closer look at tuber structure, see Dahlia Tubers: What You Need to Know. This makes it easier to see the "eyes" (the small bumps where next year’s growth will start) and helps you spot any signs of damage or rot. If you see any soft, mushy, or foul-smelling spots, trim them away with a clean knife. Only healthy, firm tubers should go into storage.
Step 5: Label Your Varieties
It is very easy to forget which tuber is which once they are out of the ground. Use a waterproof marker to write the variety name directly on the skin of the tuber, or tie a label to the stem. This ensures that when spring rolls around, you know exactly where to plant your Thomas Edison dahlias.
The same applies to Kelvin Floodlight dahlias.
Key Takeaway: Digging dahlias is best done after the first hard frost. Use a wide circle when digging to avoid damaging the fragile necks of the tubers, and always label your varieties immediately.
Curing and Storing Your Tubers
Before you tuck your tubers away for the winter, they need to "cure." This is a simple process of letting them dry out slightly so the outer skin can toughen up.
The Curing Process
Place your cleaned tubers in a cool, shaded area with good air circulation for 24 to 48 hours. Avoid placing them in direct sunlight or in a spot that is too hot, as you don't want them to shrivel. You just want the surface moisture to evaporate. A garage or a covered porch is usually a perfect spot.
Finding the Right Storage Container
Once cured, the tubers need a winter home that is cool (between 40°F and 50°F) but frost-free. Many gardeners use cardboard boxes, plastic bins with air holes, or even paper bags. To keep the tubers from drying out completely, we suggest packing them in a slightly damp medium. Popular choices include:
- Coarse vermiculite
- Pine wood shavings (the kind used for pet bedding)
- Peat moss
- Dry sand
Layer the tubers so they are not touching each other, and cover them with your chosen packing material. This creates a stable environment that mimics the soil without the risk of freezing or excess moisture.
Checking During the Winter
It is a good idea to peek at your stored tubers once a month. If they look shriveled and dry, give them a very light misting of water. If you notice any spots of mold or rot, remove the affected tuber immediately so it doesn't spread to the rest of the group. Gardening is all about observation, even during the dormant season!
To Divide or Not to Divide?
When you lift a large clump of dahlia tubers, you might wonder if you should break them apart now or wait until spring. Both methods work well, and the choice depends on your preference.
Dividing in the Fall
Some gardeners prefer to divide their tubers in the fall because the "eyes" can be easier to see on some varieties immediately after digging. Dividing now also takes up less storage space, as you are only keeping the individual tubers rather than the bulky clumps. However, the cuts you make during division create "wounds" that can be entry points for rot during storage.
Dividing in the Spring
We often recommend waiting until spring to divide. By then, the eyes are beginning to swell and are much easier to identify for beginners. Storing the clump as a whole also provides a bit of a safety net; if one part of the clump struggles, the rest is often still healthy. If you have plenty of storage space, keeping the clumps intact is the simplest and most reliable method.
Realistic Expectations for Overwintering
It is important to remember that gardening involves working with nature, which can be unpredictable. Even with the best care, not every tuber will survive the winter. Professional growers often expect a small percentage of loss due to natural variations in plant health or unexpected temperature swings.
If you are trying to keep dahlias in the ground for the first time, treat it as a fun experiment. Keep notes on which varieties survived and which didn't. Over time, you will develop a "gut feeling" for your local weather patterns and soil conditions. This hands-on experience is what transforms a beginner into a confident gardener.
Remember that weather, soil, and even the specific variety of dahlia all play a role in success. Some dahlias are naturally more robust than others. If a tuber doesn't make it through the winter, don't be discouraged. It is simply an opportunity to try a new variety or a different storage technique next year.
Why Quality Matters from the Start
Your success in overwintering dahlias often starts with the quality of the tuber you plant in the spring. A strong, healthy, and high-quality tuber from a trusted source has more stored energy and a better chance of surviving both the growing season and the dormant months.
At Longfield Gardens, we work with experienced growers to ensure you receive tubers that are true to variety and in prime condition. We maintain our own trial garden to evaluate how different plants perform, so we can provide you with the most accurate advice. Our 100% Quality Guarantee means we stand behind the plants we ship, giving you a head start on a beautiful and successful garden.
For a broader refresh on growing basics, read All About Dahlias.
Conclusion
Whether you choose to dig up your dahlia tubers or protect them in the ground, the goal is the same: to enjoy those breathtaking blooms again next year. In warmer zones, a simple layer of mulch is often all you need. In colder regions, lifting and storing the tubers is a rewarding ritual that marks the end of a successful growing season.
By paying attention to your hardiness zone, ensuring good drainage, and following the simple steps for lifting and storage, you can keep your dahlia collection growing and thriving for years to come. Gardening is an ongoing journey of learning and discovery, and every season brings new rewards.
Next Steps:
- Check your local frost date so you can plan your digging schedule.
- Gather your storage supplies, such as boxes and wood shavings, before the first frost.
- Visit our website at Longfield Gardens to explore the Dahlia Dinnerplate Daybreak Collection next spring.
"The effort you put into protecting your dahlias today is the foundation for the spectacular colors you will enjoy next summer. It is a simple way to stay connected to your garden all year long."
FAQ
How long can dahlia tubers stay in the ground after a frost?
You should aim to dig them up within two weeks after the first killing frost. While the tubers can stay in the ground as long as it hasn't frozen solid, waiting too long increases the risk of rot if the late autumn weather is particularly wet.
Can I leave dahlias in the ground in Zone 7?
Yes, it is possible, but it comes with some risk. If you have well-draining soil and apply a very thick layer (6 inches or more) of mulch, many varieties will survive a typical Zone 7 winter. However, for your favorite or most expensive plants, digging them up is the only way to be 100% sure they will survive.
What happens if I don't dig up my dahlias in a cold climate?
If the ground freezes to the depth of the tubers, the water inside the tubers will freeze and turn to ice. This causes the tuber to turn into a mushy, rotten mass once the ground thaws. Without protection or storage, dahlias in cold climates will not return the following year.
Do I need to wash the dirt off the tubers before storing them?
While some gardeners store them with the dirt on, we recommend gently washing them. Cleaning the tubers allows you to inspect them for rot or pests and makes it easier to find the "eyes" when it’s time to replant or divide them in the spring. Just be sure to let them dry completely (cure) before packing them away.