Introduction
The first time you see a dinnerplate dahlia in full bloom, it is hard not to fall in love with these spectacular plants. Their vibrant colors and intricate petal patterns make them the undisputed stars of the late-summer garden. As the season winds down and the first crisp nights of autumn arrive, many gardeners wonder how to preserve that beauty for next year. While dahlias are often treated as annuals, one of the most rewarding parts of growing them is realizing you can save the tubers to plant again.
At Longfield Gardens, we want to help you enjoy these stunning flowers year after year. While they are technically tubers rather than true bulbs, the process of "lifting" and storing them is a straightforward tradition that any gardener can master. Whether you are a beginner or a seasoned pro, taking a few simple steps in the fall ensures your favorite varieties come back even stronger next spring.
This guide will walk you through exactly what to do with dahlia bulbs in the fall, from the first frost to winter storage. We will cover the timing, the digging process, and the best ways to keep your tubers healthy during their winter nap. With a little bit of care, you can turn a single season of color into a lifetime of beautiful blooms.
Saving dahlia tubers is a simple and satisfying way to expand your garden and protect your investment in your favorite floral varieties.
Understanding Dahlia Tubers and Cold Hardiness
Before we dive into the steps, it is helpful to understand what we are working with. Although most people call them "bulbs," dahlias actually grow from tubers. These are thickened, underground stems that store energy for the plant, much like a potato. Because they have thin skins and a high water content, they are very sensitive to freezing temperatures.
In the United States, dahlia success in the winter depends largely on your USDA hardiness zone. For gardeners in zones 8 through 10, the ground rarely freezes deep enough to damage the tubers. In these warm climates, you can often leave your dahlias in the ground year-round with a thick layer of mulch for protection.
However, for those of us in zones 3 through 7, the winter cold will eventually reach the tubers and turn them into mush. In these regions, "lifting" the tubers is a necessary fall ritual. This simply means digging them up and moving them to a frost-free spot indoors. If you aren't sure which zone you are in, you can check how to overwinter dahlias to see if your local winters are mild enough for in-ground overwintering.
Timing Your Fall Tasks
One of the most common questions we receive is exactly when to start the fall process. It can be tempting to start digging as soon as the weather turns chilly, but patience is a virtue when it comes to dahlias.
The Magic of the First Frost
The best signal to start your fall dahlia care is the first killing frost. You will know it has happened because your vibrant green plants will suddenly turn black or dark brown overnight. While this might look a bit sad, it is actually a vital part of the plant’s life cycle.
The frost tells the dahlia that the growing season is over. This triggers the plant to send all its remaining energy down into the tubers, which helps them "cure" and prepares them for dormancy. At Longfield Gardens, we recommend waiting a few days to a week after this first frost before you begin digging. This short waiting period allows the tubers to toughen their skins, making them much more resilient during storage.
When Frost is Late
If you live in an area where a killing frost hasn't arrived by mid-November, you don't have to wait forever. You can go ahead and begin the process anyway. The goal is to get the tubers out of the ground before the soil itself freezes hard. If the forecast shows a deep, prolonged freeze on the way, it is time to get to work, regardless of what the foliage looks like.
Key Takeaway: The first killing frost is your best guide. Wait about 5 to 7 days after the leaves turn black before you start digging to allow the tubers to toughen up.
Step 1: Labeling and Cutting Back
The first physical step in the process is one of the most important: labeling. Once the stems are cut and the tubers are out of the ground, it is nearly impossible to tell a "Cafe au Lait" dahlia from a "Thomas Edison" variety.
Don't Lose Your Varieties
Before you cut anything, ensure every plant has a waterproof label. You can use plastic nursery tags or even wrap a piece of duct tape around the base of the stem and write the variety name with a permanent marker. This ensures that when you go to plant next spring, you know exactly which colors and heights you are putting in each garden bed.
Cutting the Stems
Once labeled, use a sharp pair of bypass pruners or loppers to cut the main stalks. 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 lift the tubers without damaging them.
Be careful not to cut the stems too low. The area where the tuber meets the stem is called the "neck," and it is also where the "eyes" (the sprouts for next year) will eventually form. Keeping a bit of the stem intact helps protect this sensitive area.
Step 2: Digging the Tubers
Digging dahlia tubers is a gentle process. Because they are brittle and full of water, they can snap easily if you are too aggressive with your tools.
Choose the Right Tools
A garden fork (pitchfork) is generally better than a shovel for this task. A shovel has a solid blade that can easily slice through a hidden tuber, whereas the tines of a fork are more likely to slide around them. If you only have a shovel, just be sure to give the plant a very wide berth.
Lifting the Clump
Start by inserting your fork into the soil about 12 inches away from the base of the stem. You want to loosen the soil all the way around the plant before you try to lift it. Slowly pry upward from different angles to break the suction of the soil.
Once the soil is loose, use one hand to grasp the stem handle and the other to lift from underneath with the fork. Gently shake off the excess large clumps of dirt. You will likely find a cluster of tubers that looks a bit like a bunch of sweet potatoes.
What to Do Next
- Remove large clumps of soil by hand or with a soft brush.
- Check for any tubers that were accidentally sliced or broken during digging and remove them.
- Move the clumps to a shaded, frost-free area like a garage or shed to dry.
Step 3: Cleaning and Curing
Once the tubers are out of the ground, they need a bit of "spa time" before they go into long-term storage. There are two schools of thought on cleaning: washing them with a hose or simply brushing off the dry dirt.
To Wash or Not to Wash?
If you have heavy clay soil, washing the tubers with a gentle stream of water from a garden hose is often necessary. It allows you to see the health of the tubers and makes it easier to spot any signs of rot. If you have light, sandy soil, you can often just let the clumps dry for a few hours and then brush away the loose dirt with your hands.
Whichever method you choose, the goal is to have clean tubers that aren't caked in wet mud, as excess moisture is the primary cause of rot during the winter.
The Curing Phase
After cleaning, let the tubers air dry for 24 to 48 hours. This is called curing. Place them on a piece of cardboard, a wooden pallet, or a newspaper in a cool, dry place that is protected from frost. Avoid placing them directly on a concrete floor, as concrete can actually pull moisture out of the tubers too quickly, causing them to shrivel.
The goal of curing is to let the outer skin dry and any small nicks or cuts "callus" over. Once they are dry to the touch, they are ready for the next step.
Step 4: To Divide or Not to Divide?
This is a point of much debate among dahlia enthusiasts. Dividing is the process of cutting the large clump into individual tubers to create more plants for next year.
Dividing in the Fall
The benefit of dividing in the fall is that the tubers are soft and easy to cut, like a potato. It also saves a lot of storage space. However, the "eyes" (the small bumps that will become next year's stems) are often very difficult to see in the fall. If you cut a tuber and it doesn't have an eye attached to a piece of the main stem, it will never grow, no matter how healthy it looks.
Dividing in the Spring
Many gardeners, including our team, often prefer to store the clumps whole and divide them in the spring. By March or April, the eyes begin to swell and turn pink or green, making it very obvious where to make your cuts. While the tubers are tougher to cut in the spring—feeling more like leather than a potato—the success rate is often higher for beginners.
If you have plenty of storage space, we recommend keeping the clumps whole for your first few seasons. It is the simplest way to ensure you have viable plants when gardening season rolls around again.
Step 5: Preparing for Winter Storage
Successful storage is all about balance. You want the tubers to stay dormant and cool, but not so dry that they shrivel up, and not so wet that they rot.
Choosing a Storage Medium
You shouldn't just throw your tubers into an empty box. They need a "bedding" material to help regulate moisture. Popular choices include:
- Peat Moss: This is a classic choice because it holds just enough moisture while still allowing for air circulation.
- Vermiculite: A mineral that is excellent at regulating moisture levels.
- Wood Shavings: Pine or cedar shavings (the kind used for pet bedding) are inexpensive and work well.
Packing the Tubers
Use a breathable container such as a cardboard box, a wooden crate, or a plastic bin with the lid left slightly ajar.
- Start with a 2-inch layer of your chosen medium at the bottom.
- Place your tubers or clumps on top, making sure they aren't crowded. It is best if they aren't touching each other.
- Cover them with more medium until they are completely buried.
- If you have a lot of tubers, you can do multiple layers, just ensure there is plenty of bedding between them.
Key Takeaway: Use a breathable container and a moisture-regulating medium like peat moss to keep tubers healthy. Avoid airtight plastic bags, which can trap moisture and cause rot.
Step 6: Finding the Perfect Storage Spot
Location is everything. The ideal storage temperature for dahlia tubers is between 40°F and 50°F.
The "Goldilocks" Zone
If the temperature stays above 60°F, the tubers may think it is spring and start to grow prematurely, or they may simply dry out and die. If the temperature drops below 35°F, you risk the tubers freezing, which is fatal.
An unheated basement, a crawl space, or a cool closet in a mudroom often works well. Attached garages can work, but you must be careful that they don't get too cold during a mid-winter deep freeze. If you store them in a garage, consider keeping the boxes on a shelf rather than the floor and wrapping the boxes in an old blanket for extra insulation.
Maintaining Your Tubers Through Winter
One of the biggest mistakes gardeners make is "setting and forgetting" their dahlias. We recommend checking on your tubers once a month throughout the winter. It only takes a few minutes and can save your entire collection.
What to Look For
When you open your boxes, look for two things: rot and shriveling.
- If you see rot: If a tuber feels mushy or has fuzzy mold on it, remove it immediately. Rot can spread quickly from one tuber to the next. If only a small part of a clump is rotten, you can sometimes cut away the bad part with a clean knife and put the rest back.
- If you see shriveling: If the tubers look wrinkled like a raisin, they are losing too much moisture. Use a spray bottle to lightly mist the storage medium with water. You don't want it to be wet, just slightly damp to the touch.
Special Considerations for Containers and Raised Beds
If you grow your dahlias in pots or raised beds, they require a slightly different approach in the fall. Because the soil in a container is elevated, it is much more exposed to the air and will freeze much faster than the ground.
Container Care
If you have the space, you can simply move the entire container into a frost-free garage or basement once the foliage has died back. Cut the stems as you would for in-ground plants and let the soil dry out completely. The dry soil in the pot acts as a natural insulator. In the spring, you can tip the pot over, harvest the tubers, divide them, and replant in fresh soil.
Raised Beds
Raised beds also freeze more quickly than the surrounding earth. If you live in a borderline zone (like Zone 7), dahlias that might survive in the ground will likely perish in a raised bed. We recommend digging and storing tubers from raised beds regardless of your zone, just to be safe.
When You Don't Have to Dig: Zones 8-10
If you are lucky enough to live in a warm climate, your fall dahlia routine is much simpler. You can leave the tubers in the ground, but they still need a little bit of care to ensure they return beautifully.
The "Cut and Cover" Method
Once the plants begin to yellow or brown in late fall, cut the stems down to about 2 or 3 inches. Do not cut them all the way to the soil line, as this can allow water to settle into the hollow stems and rot the crown.
Cover the entire area with 4 to 6 inches of mulch. You can use wood chips, straw, or fallen leaves. This mulch acts like a blanket, keeping the soil temperature stable. In the spring, once the danger of frost has passed, you can rake away the excess mulch to allow the sun to warm the soil and wake up the tubers.
Dividing In-Ground Dahlias
Even in warm climates, dahlia clumps will eventually become too large and crowded, leading to fewer flowers. We recommend digging and dividing your in-ground dahlias every two to three years. This keeps the plants vigorous and gives you plenty of extra tubers to share with neighbors or move to other parts of your yard.
Realistic Expectations for Overwintering
It is important to remember that gardening is a partnership with nature. Even with the best care, not every single tuber will survive the winter. Professional growers often expect a small percentage of loss due to natural rot or dehydration.
Don't be discouraged if a few tubers don't make it. The ones that do survive will often be larger and more productive than they were the previous year. Plus, if you store the clumps whole, you will likely have multiple tubers to work with in the spring, giving you a built-in backup.
The success of your overwintering depends a lot on your specific home environment. A basement in one house might be more humid than a basement in another. It may take a season or two of experimenting with different storage mediums (like switching from peat moss to wood shavings) to find the "sweet spot" for your home.
Summary of Fall Dahlia Care
To ensure your dahlias are ready for a successful winter, follow this simple checklist as the season ends:
- Label clearly before the first frost so you don't lose track of varieties.
- Wait for the frost to blacken the foliage, then wait another week for the tubers to cure.
- Cut stems to leave a 4 to 6-inch handle for easy lifting.
- Dig gently using a garden fork, starting a foot away from the stem.
- Clean and dry the tubers for 24-48 hours before packing.
- Store in a medium like peat moss or wood shavings in a cool, dark place (40-50°F).
- Check monthly for any signs of rot or extreme dehydration.
Conclusion
Taking the time to care for your dahlia bulbs in the fall is a rewarding investment in your garden’s future. By following these simple steps, you can save your favorite varieties and enjoy even bigger, bolder blooms next summer. At Longfield Gardens, we believe that the rhythm of the seasons—planting in the spring and tucking things away in the fall—is what makes gardening such a fulfilling journey.
Remember, the goal is simply to keep those tubers cool, dry, and frost-free. Don't worry if you don't get every step perfect the first time. Gardening is a learning process, and dahlias are surprisingly resilient. Before you know it, spring will arrive, and you will be pulling those healthy tubers out of storage, ready to start the cycle of beauty all over again.
Overwintering dahlias is a bridge between the seasons, allowing you to carry the best of this year's garden into the next.
For more inspiration and to see our latest collection of premium dahlia tubers, feel free to explore our dahlia collections and variety pages. Happy gardening!
FAQ
Do I really have to dig up my dahlias every year?
If you live in USDA zones 3 through 7, yes, you must dig them up if you want them to survive. The tubers contain a lot of water and will freeze and rot if left in cold winter soil. If you live in zone 8 or higher, you can usually leave them in the ground with a thick layer of mulch.
Can I store dahlia tubers in the refrigerator?
While a refrigerator is the right temperature (around 40°F), it is often too dry for tubers. If you choose to use a fridge, you must be very diligent about checking them for shriveling. Also, avoid storing them near ripening fruit like apples, as the ethylene gas given off by the fruit can damage the tubers.
What happens if I don't wait for a frost to dig them up?
You can dig dahlias before a frost if you need to, but the tubers may not be as hardy. The frost signals the plant to go dormant and toughens the "skin" of the tuber, which helps it survive months of storage without drying out. If you must dig early, give them an extra day or two of air-drying time.
My tubers look like shriveled raisins in mid-winter. Are they dead?
Not necessarily! If they are just slightly wrinkled, they are simply thirsty. Mist the storage medium (peat moss or shavings) with a little water to increase the humidity. As long as the tuber still feels firm and isn't brittle or hollow, it can usually be revived when you start watering it again in the spring.
