Table of Contents
- Introduction
- Understanding Your USDA Hardiness Zone
- The Benefits of Lifting Dahlia Tubers
- When Is the Right Time to Lift?
- A Step-by-Step Guide to Lifting Dahlias
- Preparing Tubers for Storage
- The Best Storage Methods
- Can You Leave Dahlias in the Ground?
- Maintenance During the Winter
- Moving Toward Spring
- Conclusion
- FAQ
Introduction
The sight of a dahlia in full bloom is one of the greatest rewards for any home gardener. From the massive, intricate petals of dinnerplate varieties to the perfectly symmetrical shapes of ball dahlias, these plants provide incredible color from midsummer right through the first weeks of autumn. As the season winds down and the weather turns crisp, many gardeners wonder how to protect these spectacular plants so they can enjoy them again next year. At Longfield Gardens, we want to help you feel confident about caring for your tubers through the coldest months of the year.
The answer to whether you should lift your dahlias depends largely on your local climate and your goals for next year’s garden. While dahlias are perennials, they are native to the warm mountain regions of Mexico and are not naturally equipped to handle deep freezes. This guide will help you determine the best winter strategy for your specific backyard, whether you choose to lift and store your tubers or try overwintering them in the ground.
By following a few simple steps, you can ensure your favorite varieties survive the winter and return even stronger in the spring. This post covers the role of hardiness zones, the step-by-step process of lifting tubers, and how to store them for the best results.
Lifting dahlia tubers is the most reliable way to ensure your favorite flowers return next year, especially in regions where the ground freezes or stays wet during the winter.
Understanding Your USDA Hardiness Zone
Before you decide whether to lift your dahlia bulbs (which are technically tubers), you need to know your USDA hardiness zone. This is the primary factor that determines if a dahlia can survive outside during the winter months. In the United States, dahlias are generally considered hardy in zones 8 through 11. In these warmer regions, the ground rarely freezes deep enough to damage the tubers.
If you live in zone 7 or colder, the winter temperatures will typically drop low enough to freeze the soil several inches deep. Because dahlia tubers are full of moisture, they will freeze, burst, and rot if left unprotected in these conditions. Even in zone 7, where some gardeners successfully overwinter dahlias with heavy mulching, lifting is still the safest bet. If you are unsure of your zone, you can find it by checking a local gardening map or visiting our Garden Basics page for more information on climate timing.
Timing is everything when it comes to winter care. Whether you are in a cold or warm climate, the plant needs to go through its natural cycle of dormancy. This process allows the tuber to store up the energy it needs to sprout again in the spring.
The Benefits of Lifting Dahlia Tubers
While lifting tubers might seem like an extra chore, it offers several benefits that go beyond simple survival. For many enthusiasts, the process of digging and storing is a favorite part of the gardening cycle. It provides a chance to inspect the health of your plants and plan for the upcoming season.
Protecting Against Rot and Pests
Winter weather isn't just about the cold. In many areas, the winter months are also the wettest. Dahlias hate "wet feet" during their dormant period. If the soil stays saturated for weeks at a time, the tubers are highly likely to rot, even if it never freezes. Lifting them allows you to keep them in a controlled, dry environment. Additionally, lifting your tubers protects them from burrowing rodents like voles, which may find a dormant tuber to be a perfect winter snack.
Opportunities for Division
One of the most exciting reasons to lift your dahlias is that it allows you to multiply your collection. A single dahlia tuber planted in the spring will grow into a large clump of several tubers by the end of summer. When you lift them in the fall, you can divide these clumps into individual tubers. This means you can have three, four, or even five times as many plants the following year for free. It is a fantastic way to fill out your garden beds or have extra plants to share with friends and neighbors.
Controlling Garden Layout
Gardens are constantly evolving. If you leave your dahlias in the ground, you are committed to having them in the same spot next year. By lifting them, you have the freedom to redesign your garden layout every spring. You can move your tall cactus dahlias to the back of a new border or relocate your favorite pompon varieties to a container near the porch.
What to do next:
- Identify your USDA hardiness zone to see if lifting is mandatory or optional.
- Monitor your local weather forecast for the first signs of frost.
- Gather your supplies, including a garden fork, labels, and storage containers.
When Is the Right Time to Lift?
Many gardeners make the mistake of digging up their dahlias too early. To get the best results, you must wait for the plant to tell you it is ready. The best indicator is the first "killing frost." This is the frost that turns the lush green foliage black or dark brown.
When the foliage dies back, the plant sends a final surge of energy down into the tubers. This "ripens" the tubers, making them tougher and better able to survive months of storage. If you dig them up while the leaves are still green and the plant is actively growing, the tubers may be too "soft" and could shrivel up in storage.
In most regions, it is best to wait about one to two weeks after the foliage has turned black before you start digging. This brief waiting period allows the "eyes" (the small bumps where next year’s stems will grow) to become more visible, which makes dividing the tubers much easier. However, if your soil is extremely wet or if a deep, sustained freeze is predicted, you should proceed with lifting as soon as the foliage has died back.
A Step-by-Step Guide to Lifting Dahlias
Lifting dahlias is a straightforward process, but it requires a gentle touch. The necks of the tubers—the narrow part where they connect to the main stem—are quite fragile. If the neck breaks, the tuber will not be able to sprout next year.
Step 1: Cut Back the Foliage
Once the frost has blackened the leaves, use a pair of clean garden shears or loppers to cut the stems. Leave about 4 to 6 inches of the stem protruding from the ground. This remaining stem acts as a handle and helps you keep track of where the clump is located while you are digging. It also provides a convenient place to attach a label so you don't forget which variety is which.
Step 2: Dig Carefully
Avoid using a pointed shovel, which can easily slice through the tubers. Instead, use a sturdy garden fork. Start digging about 12 inches away from the base of the stem. You want to give the clump a wide berth to ensure you don't accidentally stab a tuber. Gently loosen the soil all the way around the plant, lifting upward from underneath the clump.
Step 3: Lift and Clean
Once the soil is loose, use the stem "handle" to gently lift the clump out of the ground. Gently shake off any large clumps of soil. If your soil is heavy clay, you may need to use your hands to carefully pull away the dirt. You can also use a garden hose with a gentle spray to wash away the remaining soil. This makes it easier to inspect the tubers for any signs of damage or rot.
Step 4: Label Immediately
It is very easy to lose track of variety names once the tubers are out of the ground. Use a waterproof marker to write the variety name directly on the tuber or attach a plastic nursery tag to the stem with a piece of twine. At Longfield Gardens, we recommend doing this immediately to avoid confusion during the spring planting season.
Preparing Tubers for Storage
You cannot take wet, freshly dug dahlia tubers and put them directly into a box for the winter. Proper preparation is the key to preventing rot during the dormant months.
Curing the Tubers
After cleaning, the tubers need to "cure" or dry out slightly. Place them in a frost-free, well-ventilated area away from direct sunlight. A garage, basement, or shed is usually perfect. Turn the clumps upside down so that any moisture trapped in the hollow stems can drain out. Let them sit for 24 to 48 hours. The goal is to have the skin of the tuber feel dry to the touch, but the tuber itself should still feel firm like a potato.
Inspecting for Health
Before packing them away, take a close look at each clump. Use a clean knife to trim off any thin, hairy "feeder" roots and any tubers that feel mushy or look shriveled. If you see any signs of rot (brown or black soft spots), cut that section away until you reach clean, white flesh. If a tuber is completely soft, discard it entirely to prevent the rot from spreading to the healthy ones.
The Best Storage Methods
The goal of winter storage is to keep the tubers dormant, cool, and slightly hydrated. If the storage area is too warm, the tubers will try to grow. If it is too dry, they will shrivel up. If it is too wet, they will rot. The ideal temperature range is between 40°F and 50°F.
Choosing a Storage Medium
To maintain the right moisture balance, most gardeners pack their tubers in a "storage medium." Common options include:
- Peat Moss: This is the most popular choice as it holds a small amount of moisture without becoming soggy.
- Vermiculite: A lightweight mineral that provides excellent aeration and moisture control.
- Sawdust or Wood Shavings: Ensure these are clean and not from treated lumber.
- Newspaper: Wrapping individual tubers in several layers of dry newspaper can work well in humid basements.
Packing the Containers
Use a breathable container such as a cardboard box, a plastic bin with holes drilled in the sides, or a wooden crate. Start with a 2-inch layer of your chosen medium. Place the tubers in a single layer so they are not touching each other. This prevents a single rotting tuber from ruining the entire batch. Cover them with another layer of the medium and repeat until the container is full.
Key Takeaway: The "Goldilocks" environment for dahlia storage is 40–50°F: not too cold to freeze, not too warm to sprout, and just dry enough to prevent rot.
Can You Leave Dahlias in the Ground?
If you live in a warmer climate (Zone 8 and above) or if you simply enjoy taking a bit of a gardening gamble, you might choose to leave your dahlias in the ground. While this is less work, it does require some "winterizing" to improve the odds of survival.
Heavy Mulching
The best way to protect dahlias in the ground is to provide a thick "blanket" of insulation. Once you have cut the stems down to the ground, cover the area with 6 to 10 inches of mulch. You can use wood chips, shredded leaves, or straw. This layer helps keep the soil temperature stable and prevents the ground from freezing around the tubers.
Drainage Concerns
If you choose to leave them in the ground, ensure the area has excellent drainage. If the spot collects standing water during winter rains or snowmelt, the tubers will almost certainly rot. Some gardeners place a piece of plastic or a tarp over the mulched area to redirect excess rain away from the tubers, though you must ensure there is still some airflow to prevent mold.
The Risk of Crowding
Keep in mind that if you leave dahlias in the ground for several years, the clumps will become very large and crowded. Over time, this leads to smaller flowers and weaker stems because the tubers are competing for nutrients. Even in warm climates, it is a good idea to dig and divide your dahlias every 2 to 3 years to maintain the vigor of the plant.
Maintenance During the Winter
Dahlia storage is not a "set it and forget it" task. We suggest checking on your stored tubers at least once a month during the winter. This simple check-up can save your entire collection.
Open your boxes and feel a few of the tubers. If they feel mushy or smell foul, they are rotting. Remove any affected tubers immediately and discard them. If the storage medium feels very damp, leave the box open for a few days to let it dry out.
On the other hand, if the tubers feel very light and look shriveled, they are getting too dry. You can lightly mist the storage medium with a spray bottle of water. Be careful not to overdo it; you just want to add a tiny bit of humidity, not make the medium wet. If the tubers are only slightly shriveled, don't worry—they usually plump back up once they are planted in the spring.
Moving Toward Spring
As the days begin to get longer and the threat of a hard freeze passes, you can start thinking about replanting. In most regions, this happens in late April or May, once the soil has warmed up to about 60°F.
If you have lifted your tubers, you may notice small pink or white "eyes" starting to sprout in late winter. This is a sign that the tubers are waking up. If you want to get a head start on the season, you can plant your tubers in pots indoors about 4 to 6 weeks before the last frost date. This gives you a jumpstart on growth, leading to earlier blooms in the summer. When it's time to move them outside, remember that dahlias love sun and well-draining soil. Following the right plant, right place principle will ensure your garden stays beautiful all season long.
Conclusion
Whether you choose to lift your dahlia bulbs or protect them in the ground, the goal is the same: preserving the beauty and health of your plants for another year of enjoyment. For gardeners in northern climates, lifting is an essential part of the yearly rhythm that guarantees a successful display. In warmer areas, a little extra mulch might be all you need. Regardless of your zone, taking the time to care for your tubers over the winter is a rewarding process that results in bigger, better blooms.
- Know your hardiness zone to decide if lifting is necessary.
- Wait for the first frost to ensure tubers are dormant and "ripened."
- Store tubers in a cool, dark, and slightly humid environment.
- Check periodically for rot or dehydration throughout the winter.
Longfield Gardens is here to support you with high-quality tubers, dahlia collections and the practical advice you need to grow them successfully. With a little bit of winter preparation, your garden will be ready to burst into color once the spring sun returns.
Gardening is a journey of observation and care. Taking the time to protect your dahlias in the winter is an investment that pays off in a spectacular summer display.
FAQ
Can I leave dahlias in the ground if I live in Zone 7?
In Zone 7, leaving dahlias in the ground is a risk, but it can be successful if the winter is mild and the soil is well-drained. To improve your chances, apply a very thick layer of mulch (at least 8 inches) and consider covering the area with a waterproof tarp to prevent rot. However, lifting is still the only way to guarantee they will survive a particularly harsh or wet winter.
What happens if I dig my dahlias before the first frost?
Digging dahlias while they are still actively growing can result in tubers that haven't stored enough energy for dormancy. These "green" tubers are more likely to shrivel or rot during the winter because their skins haven't toughened up yet. If you must dig early due to travel or scheduling, try to wait as late as possible and be extra diligent about your storage conditions.
Can I store dahlia tubers in plastic bags?
We do not recommend storing dahlia tubers in sealed plastic bags. Dahlias are living organisms that need to "breathe" even when they are dormant. Sealed bags trap moisture, which creates a perfect environment for mold and rot. If you prefer using plastic, use a bin or bag with many holes to allow for consistent air circulation.
Why did my stored dahlia tubers turn into mush over the winter?
The most common cause of "mushy" tubers is rot brought on by too much moisture or freezing temperatures. This can happen if the tubers weren't dried properly before storage, if the storage medium was too wet, or if the storage area dropped below 32°F. To prevent this, ensure your tubers are cured for 24–48 hours and check them monthly to remove any that show early signs of decay.