Table of Contents
- Introduction
- Understanding Dahlia Hardiness
- How Soil and Moisture Affect Your Decision
- Reasons to Dig Even if You Don't Have To
- When is the Right Time to Dig?
- A Step-by-Step Guide to Digging Your Dahlias
- Preparing Dahlias for Winter Storage
- The Importance of Labeling
- Growing Dahlias in Containers
- Troubleshooting Winter Storage
- Dividing Your Tubers: A Rewarding Bonus
- Enjoying the Cycle of the Garden
- Conclusion
- FAQ
Introduction
There is nothing quite like the feeling of walking into your garden on a warm August morning to find your first dinnerplate dahlia in full bloom. These spectacular flowers, with their intricate petals and vibrant colors, are the highlights of the summer season. At Longfield Gardens, we believe every gardener should experience the reward of growing these stunning plants, whether you have a large backyard or a few sunny pots on a patio.
As autumn approaches and the air turns crisp, many gardeners begin to wonder about the best way to care for their plants through the winter. The question of whether you need to dig up your dahlia tubers—often called dahlia bulbs—is one of the most common topics we encounter. The answer depends on your local climate, your soil type, and how much effort you want to put into next year’s display.
This guide is designed to help you determine the best winter strategy for your specific garden. We will cover the differences between hardiness zones, how to protect your plants in the ground, and the simple steps for lifting and storing them if your winters are cold. Our goal is to make dahlia care feel like a natural, enjoyable part of your gardening routine so you can look forward to even more blooms next year.
Understanding Dahlia Hardiness
To answer the question of whether you have to dig up your dahlia bulbs, we first need to look at where these dahlias come from. Dahlias are native to the high plains of Mexico and Central America. In their natural habitat, the ground rarely freezes, and the soil stays relatively dry during the dormant season. Because of this heritage, dahlias are considered "tender perennials" in most of the United States.
In gardening, "hardiness" refers to a plant's ability to survive the winter cold. Most dahlias are only hardy in USDA zones 8 through 11. In these warmer regions, the ground stays warm enough that the tubers can safely remain in the garden year-round. However, if you live in zone 7 or colder, the freezing temperatures of winter can damage or kill the tubers if they are left unprotected.
While zones provide a helpful starting point, they are not the only factor. Your local microclimate—the specific conditions in your own yard—plays a huge role. For example, a dahlia planted against a south-facing brick wall might survive in a zone where others wouldn't, simply because the wall holds and radiates heat throughout the night.
Key Takeaway: The decision to dig depends mostly on your USDA hardiness zone. If you are in zone 8 or warmer, you can usually leave them. In zone 7 or colder, digging is the safest way to ensure they return.
How Soil and Moisture Affect Your Decision
It is a common misconception that cold is the only thing that kills dahlias in the winter. In reality, moisture is often the bigger threat. Even in warmer climates like zone 8 or 9, dahlias can struggle if the soil stays saturated for long periods.
Dahlias have "tubers," which are thick, fleshy root structures that store energy. These tubers are very sensitive to "drainage," which is a term gardeners use to describe how fast water leaves the soil. If your garden has heavy clay soil that stays wet and soggy, the tubers are likely to rot before spring arrives.
If you have sandy soil that drains quickly, your dahlias have a much better chance of surviving a wet winter in the ground. Before deciding to leave your tubers out for the season, observe your garden after a heavy rain. If water puddles and stays on the surface for hours, it is much safer to dig the tubers up and store them in a dry place.
The Role of Mulch
For those living on the edge of hardiness—specifically in USDA zone 7—mulch can be a game-changer. Mulch acts like a warm blanket for the soil, preventing the frost from penetrating deep enough to reach the tubers.
If you choose to leave your dahlias in the ground in a marginal zone, you should apply a thick layer of organic material over the planting site. Good options include:
- Shredded bark or wood chips
- Straw or salt hay
- Clean, dry leaves
- Pine needles
A layer of mulch 4 to 6 inches deep can keep the soil temperature several degrees warmer than the surrounding air. This simple step is often enough to help a dahlia survive a typical zone 7 winter.
Reasons to Dig Even if You Don't Have To
Even if you live in a warm climate where dahlias are hardy, there are several excellent reasons why you might choose to dig them up anyway. Gardening is about more than just survival; it is about helping your plants thrive.
Preventing Overcrowding
When you leave a dahlia in the ground year after year, the tuber clump continues to grow and expand. Over time, these clumps can become massive and congested. An overcrowded dahlia clump often produces smaller flowers and weaker stems because the many different "eyes" (the points where new growth starts) are all competing for the same nutrients and space.
Digging up the tubers gives you the opportunity to "divide" them. Dividing is the process of cutting a large clump into several smaller pieces. This keeps the plants vigorous and, as a bonus, gives you free plants to put in other parts of your garden or to share with friends.
Better Soil Preparation
Digging up your tubers allows you to refresh the soil in your flower beds. Dahlias are heavy feeders that love rich, organic matter. When the tubers are out of the ground, it is the perfect time to dig in some fresh compost or aged manure. This ensures that when you replant in the spring, your dahlias have all the fuel they need for a spectacular show.
Protecting Against Pests
In some regions, leaving tubers in the ground makes them an easy target for soil-dwelling pests like voles or certain types of beetle larvae. By lifting the tubers and storing them in a protected environment, you remove them from the "winter buffet" that some critters rely on.
What to do next:
- Check your USDA hardiness zone on a map.
- Assess your soil drainage after the next rain.
- Decide if you want to expand your garden by dividing your tubers this year.
When is the Right Time to Dig?
Timing is one of the most important parts of successful dahlia care. If you dig too early, the tubers may not have stored enough energy to last through the winter. If you wait too long, a deep freeze might damage the crown of the plant.
The best signal is the weather. Most gardeners wait for the first "killing frost." This is a frost that is cold enough to turn the green dahlia foliage black or dark brown. When the top of the plant dies back, it sends a signal to the tuber to go dormant.
After the first frost, it is common practice to wait about 5 to 10 days before digging. During this week of waiting, the tubers undergo a "curing" process while still in the ground, which helps toughen their skins for storage. However, if your forecast calls for a deep freeze (temperatures staying well below freezing for 24 hours or more), do not wait—get those tubers out of the ground!
A Step-by-Step Guide to Digging Your Dahlias
At Longfield Gardens, we want the process of lifting your tubers to be a satisfying end-of-season ritual rather than a chore. Following a simple, step-by-step method ensures your tubers stay healthy and ready for next year.
Step 1: Cut Back the Foliage
Start by cutting off the main stalks of the plant. Use a sharp pair of loppers or hand pruners. You should leave a "handle" of about 4 to 6 inches of stem sticking out of the ground. This handle makes it much easier to move the tuber clump without damaging the fragile necks of the individual tubers.
Step 2: Loosen the Soil
Avoid using a sharp shovel if possible, as it is easy to accidentally slice through a tuber. A garden fork (or pitchfork) is the best tool for the job. Start digging about 12 inches away from the main stem. Push the fork deep into the soil and gently pry upward. Work your way all the way around the plant until the soil is loose and the clump begins to lift.
Step 3: Lift with Care
Once the soil is loose, reach down and grab the "handle" you left behind. Gently lift the entire clump out of the hole. Dahlias can be surprisingly heavy, so take your time. If the clump feels stuck, use your garden fork to loosen the soil a bit more. Never yank the plant, as the connection between the tuber and the stem (the neck) is very fragile. If the neck breaks, the tuber may not be able to sprout next year.
Step 4: Clean the Tubers
Gently shake the clump to remove large chunks of soil. Some gardeners prefer to use a garden hose to wash the remaining dirt away. This makes it much easier to see the "eyes" if you plan on dividing them. If you do wash them, make sure to let them dry completely in a shaded, frost-free area before moving them to storage.
Key Takeaway: Using a garden fork instead of a shovel and leaving a stem "handle" are the two best ways to prevent damage during the digging process.
Preparing Dahlias for Winter Storage
Once your tubers are out of the ground and cleaned, they need a short period of "curing" before they go into their final winter home. Curing simply means letting the tubers sit in a cool, dry place for a few days. This allows any excess moisture on the skin to evaporate and helps small nicks or scratches to "callous" over, which prevents rot.
Choosing a Storage Container
The goal of storage is to keep the tubers cool and dormant without letting them dry out completely or get so wet that they mold. You have several options for containers:
- Cardboard Boxes: These are breathable and very effective for most home basements.
- Plastic Bins: If you use plastic, leave the lid slightly ajar or drill air holes to prevent moisture buildup.
- Paper Bags: Good for small quantities, though they offer less protection against temperature swings.
Selecting a Packing Medium
You shouldn't just throw the tubers into a box by themselves. Packing them in a medium helps regulate humidity and provides insulation. Our favorite options at Longfield Gardens include:
- Vermiculite: A lightweight mineral that is excellent at managing moisture.
- Peat Moss: A classic choice, though it can be dusty to work with.
- Cedar Shavings: Often sold as pet bedding, these smell great and have natural anti-fungal properties.
- Pine Shavings: A budget-friendly alternative that works very well.
Layer the medium in the bottom of your container, place the tubers on top so they aren't touching each other, and then cover them with more medium. This "nesting" approach protects them from rot spreading from one tuber to another.
Finding the Perfect Spot
The ideal storage location is cool, dark, and dry. You are looking for a temperature range between 40°F and 50°F.
- Unheated Basements: Usually the best option for most homeowners.
- Root Cellars: Perfect, as long as they aren't too damp.
- Attached Garages: Can work, but be careful that they don't get too cold during a deep freeze.
Avoid storing tubers in a standard refrigerator (too cold and dry) or a heated living space (too warm, which will cause them to sprout or shrivel).
The Importance of Labeling
It is easy to think you will remember which tuber is which, but by mid-winter, every dahlia tuber looks remarkably similar. Labeling is a simple step that saves a lot of confusion in the spring.
You can write the variety name directly on the skin of the tuber using a soft pencil or a permanent marker. Alternatively, you can use garden tags tied loosely around the stem handle. If you are storing multiple varieties in one box, use dividers or separate bags to keep them organized. Knowing which dahlias are tall, short, or specific colors makes planning your spring garden much easier and more exciting.
Growing Dahlias in Containers
If you grow your dahlias in pots, you have a slightly different set of options. For many people, the easiest way to "dig" container dahlias is to simply move the entire pot into a frost-free area like a garage or basement.
- Wait for the foliage to die back after a frost.
- Cut the stems down to 2 inches.
- Move the pot to a cool, dark place.
- Stop watering entirely.
The soil in the pot will dry out, and the tubers will go dormant. In the spring, you can tip the pot over, remove the tubers, divide them if necessary, and replant them in fresh soil. This is an excellent "low-effort" way to overwinter dahlias if you only have a few plants.
Troubleshooting Winter Storage
Even with the best care, sometimes things don't go perfectly. Checking on your tubers once a month during the winter is a great habit to start. It only takes a few minutes and can save your collection.
If Tubers Look Shrivelled
If the tubers look like a wrinkled raisin, they are losing too much moisture. This usually happens if the storage area is too dry or the packing medium isn't holding enough humidity. The fix is easy: lightly mist the packing medium with a spray bottle of water. You don't want it wet, just slightly damp to the touch.
If You See Mold or Rot
If a tuber feels mushy or has visible fuzzy mold, remove it immediately. Mold can spread quickly to healthy tubers nearby. If only a small part of a tuber is soft, you can sometimes cut that part away with a clean knife and let the remaining piece air-dry before putting it back. If the "neck" or "crown" is rotten, it is best to discard that tuber and focus on the healthy ones.
If They Start to Sprout
If you see green growth in February or March, your storage area is likely a bit too warm. Move the container to a cooler spot if possible. A little bit of sprouting is okay as spring approaches, but you want to keep them dormant as long as possible to preserve their energy for the garden.
Dividing Your Tubers: A Rewarding Bonus
One of the most exciting parts of digging up your dahlias is the chance to divide them. A single tuber planted in May will often grow into a clump of 5 to 10 tubers by October.
To divide them, you need to find the "eyes." The eye is a small bump or swelling located on the crown (where the tuber meets the stem). It looks very similar to the eye on a potato. Each division must have at least one eye, a healthy neck, and a fleshy body.
Many gardeners find it easier to divide in the spring when the eyes begin to swell and become more visible. However, if you are short on storage space, dividing in the autumn is perfectly fine. Just make sure to let the cut surfaces dry and callous for 24 hours before packing them away.
Enjoying the Cycle of the Garden
Gardening is a series of seasons, each with its own rhythm. While saying goodbye to your dahlia blooms in the fall can feel a bit sad, the process of tucking them away for winter is a bridge to next year’s success. Whether you decide to leave them in the ground with a thick layer of mulch or lift them into boxes for the winter, you are taking an active role in the health of your garden.
By understanding the needs of your plants and responding to your local climate, you take the guesswork out of the process. Gardening shouldn't be stressful; it should be a rewarding way to connect with nature. At Longfield Gardens, we are here to support you with quality plants and practical advice every step of the way. When spring returns, you will be rewarded with healthy tubers ready to explode into another season of breathtaking color.
Final Takeaway: Most dahlia success comes from getting the basics right. Keep them dry, keep them cool, and keep them labeled.
Conclusion
Deciding whether to dig up your dahlia bulbs is a choice that depends on your climate and how you like to garden. In warmer zones, a simple layer of mulch is often all you need for a successful return next year. In colder regions, lifting the tubers is an easy win that protects your investment and gives you the chance to grow your collection through division. No matter which path you choose, the effort is well worth it when those first giant blooms appear in mid-summer.
- Check your hardiness zone to determine if digging is necessary.
- Ensure soil drainage is adequate if leaving tubers in the ground.
- Use a garden fork to lift tubers gently and avoid neck damage.
- Store tubers in a cool, dark place between 40°F and 50°F.
We hope this guide makes your autumn garden prep feel simple and successful. For more tips on growing beautiful flowers, explore our other planning guides.
"The wait for spring is always worth it when you know your favorite flowers are safe and ready to bloom again."
FAQ
Can I leave dahlias in the ground in Zone 7?
Yes, it is possible to leave dahlias in Zone 7, but it comes with some risk. To increase their chances of survival, plant them in a well-drained area and cover the site with 4 to 6 inches of mulch, such as straw or wood chips, after the first frost. If your winter is exceptionally wet or cold, digging them up is still the safest option.
What happens if I don't dig up my dahlias in a cold climate?
In USDA zones 6 and colder, the ground usually freezes deep enough to reach the dahlia tubers. Since these tubers are mostly water, the freezing temperatures cause the cells to burst, turning the tuber into a mushy, rotten mess when it thaws. If you live in a cold area and don't dig them, you should treat them as annuals and plan to plant new ones in the spring.
Do I need to wash the dirt off the tubers before storing them?
Washing is optional but can be very helpful. Removing the soil allows you to inspect the tubers for damage or rot and makes it much easier to see the "eyes" for dividing. If you choose to wash them, ensure they are completely dry before you pack them in storage medium, as trapped moisture can lead to mold.
How often should I check my stored dahlia tubers?
It is a good idea to check your tubers once a month throughout the winter. Look for signs of shriveling, which means they need a light misting of water, or signs of rot, which means you should remove the affected tuber. This quick monthly check ensures that small issues don't turn into big problems before planting time arrives.