Introduction
Few sights in the garden compare to the arrival of summer dinnerplate varieties. From the massive, intricate petals of dinnerplate varieties to the perfectly geometric shapes of pompon types, these flowers bring a level of color and excitement that defines the late-season landscape. Because they are so rewarding to grow, it is only natural to want to keep that beauty going year after year.
At Longfield Gardens, we know that many home gardeners find the idea of winterizing dahlias a bit mysterious at first. If you love neat, round blooms, the PomPon Dahlia collection is a great place to start. However, the process is quite straightforward once you understand what the plants need during their rest period. Whether you are a beginner or an experienced grower, taking a few simple steps in the fall ensures your favorite varieties return even stronger next season.
This guide covers everything you need to know about protecting your dahlia tubers from the winter cold. We will walk through when to start the process, how to safely remove them from the garden, and the best ways to store them until spring. By following these practical steps, you can enjoy a lifetime of blooms from a single investment.
Determining Your Winterizing Strategy
The first step in winterizing dahlias is deciding whether you need to dig them up or if they can stay in the ground. This choice depends primarily on your local climate and your soil conditions. Dahlias are native to the warm mountain regions of Mexico and Central America, which means they are not naturally equipped to survive deep-frozen soil.
In USDA hardiness zones 8 through 11, the ground usually stays warm enough that you can leave your tubers in place. In these warmer regions, winterizing is as simple as cutting back the foliage and applying a layer of mulch to keep the soil temperature stable. If you live in zone 7, you are in a "swing" area; in a mild winter with well-drained soil, dahlias often survive with heavy protection, but many gardeners choose to dig them up just to be safe. For a broader look at the flower forms themselves, browse the Dahlia Collections.
For those of us in zones 3 through 6, digging and storing tubers is a necessity. If the ground freezes several inches deep, the water inside the dahlia tuber will freeze, expand, and turn the tuber into a mushy, non-viable clump by spring. While digging them up takes a bit of effort, it is a rewarding task that allows you to inspect your plants, divide them to get more flowers for free, and ensure a healthy start for the following year.
Timing Your Winterizing
Success with dahlias starts with patience. It can be tempting to clear the garden as soon as the weather turns chilly, but dahlias benefit from staying in the ground as long as possible. The tubers use the shorter days and cooler temperatures of autumn to store energy. For a big-flower look, the Dahlia Dinnerplate High Summer Mix is a colorful option.
The best signal to start winterizing is the first hard frost. You will know it has happened when the lush green foliage of your dahlias suddenly turns black or dark brown and goes limp. This might look a bit sad, but it is actually a vital part of the plant’s life cycle. This "killing frost" tells the plant to go into deep dormancy.
We recommend waiting about 3 to 7 days after this first frost before you begin digging. This short waiting period allows the "eyes"—the small bumps on the tuber that will become next year's stems—to become more prominent. If you live in a region where a hard frost comes very late, you can aim to dig them up by mid-November, as the plants will naturally slow down as the soil cools.
Key Takeaway: Wait for the first hard frost to turn the foliage brown before you begin the winterizing process. This ensures the tubers have stored maximum energy for next year’s growth.
Step-by-Step Digging Process
When the time comes to lift your tubers, the goal is to be as gentle as possible. Dahlia Assorted Sedona Collection offers warm, coordinated color for gardeners planning ahead. Dahlia tubers are often described as looking like a bunch of sweet potatoes, but they are much more brittle. The most important part of the tuber is the "neck," which is the thin area where the tuber connects to the main stem. If the neck snaps, the tuber usually cannot grow, even if it looks healthy otherwise.
Step 1: Cut Back the Stems
Before you touch the soil, use a pair of clean, sharp loppers or bypass pruners to cut the dahlia stems down to about 4 to 6 inches above the ground. This remaining "handle" makes it easier to move the clump around and helps you keep track of where the center of the plant is. Some gardeners like to wait a few days after cutting before digging to allow the tubers to "cure" slightly in the ground, but you can also proceed immediately.
Step 2: Loosen the Soil
Using a garden fork is much safer than using a spade. A spade has a sharp, solid blade that can easily slice through a tuber you can't see. A garden fork allows you to gently probe the soil. Start your digging about 12 inches away from the base of the stem. Digging too close is the most common way tubers get damaged.
Insert the fork deeply into the soil and gently pry upward. Work your way around the entire plant in a circle, loosening the earth as you go. You want the whole root mass to feel loose and buoyant before you try to lift it.
Step 3: Lift the Clump
Once the soil is thoroughly loosened, reach down and place your hands under the clump rather than pulling on the stem handle. Lift the entire mass out of the ground. Don't worry if a few small tubers break off during this process—large, healthy plants often produce more than they need to survive.
What to Do Next:
- Remove any large chunks of soil by hand.
- Check that your variety labels are still attached to the stems.
- Place the clumps in a wheelbarrow or on a garden tarp.
- Move the tubers to a frost-free area, like a garage or shed, to begin the cleaning process.
Cleaning and Curing Your Tubers
Once your dahlias are out of the ground, they need a little bit of grooming before they go into storage. There are two schools of thought on cleaning: some gardeners prefer to leave the soil on to provide a natural protective barrier, while others prefer to wash them clean to inspect for pests or rot.
If your soil is heavy clay, we find it is usually best to wash the tubers. Use a garden hose with a gentle spray setting to rinse away the dirt. This allows you to see the health of the tubers clearly. Look for any parts that feel soft, mushy, or smell sour—these are signs of rot and should be trimmed away with a clean knife. For another vivid mix, the Dahlia Assorted Sangria Collection is another ready-made choice.
After cleaning, the tubers need to "cure." This just means letting them dry out so they don't develop mold in storage. Place the clumps upside down on a tray, a piece of cardboard, or a screen. Turning them upside down allows any moisture trapped in the hollow stems to drain out. Keep them in a cool, dry, and dark place for about 2 to 3 days. Do not leave them in direct sunlight, as this can cause the skins to shrivel too quickly.
Understanding the "Eyes" and Dividing
One of the most exciting parts of winterizing dahlias is the opportunity to multiply your collection. A single tuber planted in May can turn into a clump of 5 to 10 tubers by October. However, not every tuber in the clump will grow into a new plant. To grow, a tuber must have an "eye."
The eyes are small, dormant buds located on the crown of the plant—the area where the individual tubers meet the main stem. They look like the tiny bumps on a potato. If you divide a tuber and it doesn't have a piece of the crown with an eye attached, it will never sprout.
Many gardeners choose to wait until spring to divide their dahlias because the eyes become much easier to see as they begin to swell with the warmth of the new season. However, if you are short on storage space, dividing in the fall is a great option. If you choose to divide now, use a sharp, sterilized knife and ensure each piece has at least one tuber, a solid neck, and a visible eye.
Choosing Your Storage Method
The goal of storage is to keep the tubers in a state of suspended animation. They need to stay cool enough that they don't start growing, but warm enough that they don't freeze. They also need enough humidity that they don't turn into dry "mummies," but enough air that they don't rot.
The ideal temperature for dahlia storage is between 40°F and 50°F. An unheated basement, a root cellar, or a crawl space is often the perfect environment. If you use a garage, make sure it is insulated; a single night of 20°F temperatures can ruin your entire collection. For a complete walkthrough, see How to Overwinter Dahlia Tubers.
Method 1: The Packing Medium Method
This is the most common approach. Place your cured tubers in a container—like a cardboard box, a plastic bin with the lid left slightly ajar, or a paper bag. Surround the tubers with a slightly damp (but never wet) medium. Popular choices include:
- Coarse Vermiculite: This is excellent at regulating moisture.
- Peat Moss: A classic choice that provides good insulation.
- Pine Shavings: Often sold as animal bedding, these provide great airflow.
- Potting Soil: Use a fresh, lightly damp mix if you have extra on hand.
Method 2: The Plastic Wrap Method
Some gardeners have great success by wrapping individual, cleaned, and dried tubers tightly in plastic kitchen wrap (Saran wrap). This method relies on the tuber's own internal moisture to keep it viable. It is a space-saver and makes it easy to see if any individual tuber is starting to rot without disturbing the whole batch.
Method 3: Storing Container-Grown Dahlias
If you grow your dahlias in pots, winterizing is even easier. Once the foliage has died back from the frost, cut the stems to the soil level. You can simply move the entire pot into a cool, dark, frost-free area like a basement. The soil in the pot acts as a natural insulator. In the spring, you can tip the pot out, refresh the soil, and start the growing process again.
Key Takeaway: The perfect storage spot is dark, stays between 40-50°F, and keeps the tubers from drying out completely.
Winterizing Dahlias in the Ground (Zones 7-11)
If you are lucky enough to live in a climate where the ground doesn't freeze hard, you can save yourself the digging and let your dahlias sleep in their garden beds. However, "winterizing" still requires a little bit of preparation to protect them from winter rain and occasional cold snaps.
Excessive moisture is the biggest enemy of dahlias left in the ground. If your soil is heavy or the spot stays soggy, the tubers are likely to rot before spring. To prevent this, many gardeners in these zones create a "mulch sandwich."
After cutting the stems down to a few inches, cover the area with a generous layer of mulch. Use 4 to 6 inches of straw, wood chips, or shredded leaves. This acts like a blanket, keeping the soil temperature consistent. In areas with very wet winters, some people even place a piece of scrap plywood or a small tarp over the dahlia bed to divert heavy rain away from the dormant tubers.
Mid-Winter Check-Ins
Winterizing isn't quite a "set it and forget it" task. We recommend checking on your stored tubers about once a month. This small habit can save your collection if conditions change.
When you open your storage boxes, look for two things:
- Signs of Rot: If a tuber feels soft, looks fuzzy with mold, or smells bad, remove it immediately. One rotting tuber can quickly spread decay to its neighbors. If you catch it early, you can often just trim the bad part off and let the rest of the clump continue its nap.
- Signs of Shriveling: If the tubers look wrinkled like a raisin, they are losing too much moisture. Use a spray bottle to lightly mist the packing medium with water. You don't want the tubers to be wet, just for the air around them to be slightly more humid.
If you notice a lot of condensation inside a plastic storage bin, the lid is on too tight. Move it slightly to one side to allow more air to circulate. It is all about finding that perfect balance of "not too dry" and "not too wet."
Preparing for Spring
As winter begins to fade and the days get longer, your dahlias will naturally start to wake up. By late March or April, you may see tiny pink or green sprouts beginning to emerge from the eyes of your tubers. This is an exciting sign that your winterizing efforts were successful.
When the soil in your garden reaches about 60°F and the danger of frost has passed, you can bring your tubers out of storage. This is a great time to divide them if you haven't already. At our trial gardens, we often find that starting tubers in pots indoors about 4 weeks before the last frost date gives the plants a wonderful head start, leading to earlier blooms in the summer. For more on that approach, see 8 Tips for Growing Better Dahlias.
Conclusion
Winterizing dahlia bulbs is a simple ritual that connects the end of one gardening season to the beginning of the next. While it involves a bit of physical work in the fall, the reward is a garden filled with spectacular, familiar blooms that feel like old friends returning for the summer. By following the basics of timing, gentle digging, and cool storage, you can keep your favorite varieties thriving for many years to come.
- Wait for a hard frost to signal dormancy before digging.
- Use a garden fork to lift tubers gently, starting 12 inches away from the stem.
- Clean and cure the tubers for 2-3 days before packing them away.
- Store in a cool, dark place (40-50°F) using a medium like peat moss or vermiculite.
- Check your tubers once a month to ensure they stay healthy and hydrated.
At Longfield Gardens, our goal is to help you grow a more beautiful world, one season at a time. Gardening is a journey of learning and growth, and All About Dahlias is a helpful next step for mastering the care of dahlias. We are here to support you with quality plants and practical advice every step of the way.
Next Step: Check your local frost dates today so you can mark your calendar for when to begin your dahlia winterizing routine.
FAQ
Can I leave my dahlias in the ground if I live in Zone 6?
In Zone 6, leaving dahlias in the ground is risky because the soil usually freezes deep enough to reach and kill the tubers. While a very mild winter or exceptionally heavy mulching might allow them to survive, we generally recommend digging them up to ensure you don't lose your favorite varieties.
What happens if I don't wait for a frost to dig them up?
You can dig up dahlias before a frost, but the tubers may not be as hardy. The period of cooling temperatures in the fall helps the tuber develop a thicker "skin" and store the starches it needs for winter. If you must dig early, ensure you give them extra time to cure in a cool, dark place before packing them.
Why did my stored dahlia tubers turn into mush?
Mushy tubers are usually a sign of rot caused by too much moisture or freezing temperatures. If the tubers were not dried properly before storage, or if the packing medium was too wet, fungus and bacteria can take hold. Always ensure they are dry to the touch and stored in a frost-free location between 40°F and 50°F.
Do I have to wash the dirt off the tubers before storing them?
No, washing is not strictly necessary. Many gardeners find that leaving a bit of soil on the tubers provides a helpful buffer against drying out. However, if your soil is very wet or contains pests like slugs, washing them helps you identify and remove potential problems before they spend the winter in a storage box.
