Introduction
Few sights in the garden compare to the exuberant colors and intricate forms of dahlias in full bloom. From the giant "dinnerplate" varieties to the tight, geometric petals of pompons, these plants often become the centerpiece of the summer landscape. At Longfield Gardens, we believe that the joy of growing these flowers shouldn't end when the first autumn chill arrives. Saving your favorite tubers is a rewarding way to ensure your garden returns even more beautiful next year.
Removing tubers from the ground at the right time is the most important step in successful overwintering. If you dig too early, the tubers may be immature and shrivel in storage. If you wait too long, a deep freeze could damage the crown and prevent growth next spring. This guide will help you identify the perfect window for your USDA hardiness zone, how to read the plant's signals, and the best way to lift them safely.
Timing your dahlia harvest correctly ensures that the plant has moved all its energy into the tuber for a long winter’s nap.
Reading the Signs of the Season
Dahlias are native to the high plains of Mexico and Central America. They love warm days and cool nights, but they are not equipped to survive a freezing winter in most of the United States. As the days grow shorter and the temperatures drop, the plant begins a natural transition. It stops putting energy into new green growth and flowers. Instead, it starts moving starches and sugars down into the root system.
This process is essential for tuber maturity. A mature tuber has a thicker skin and more stored energy, making it much more likely to survive months in storage without drying out. To get the timing right, you need to watch the weather forecast and the physical appearance of your plants.
The First Light Frost
The first sign that it is time to think about removal is usually a light frost. A light frost occurs when temperatures dip just below 32°F for a short period. You will notice that the top leaves of your dahlias may turn black or brown, and any remaining flowers will wilt. This is not a cause for alarm. In fact, it is a helpful signal. For a step-by-step refresher, see How to Overwinter Dahlia Tubers.
When the foliage is hit by frost, it tells the plant to go into dormancy. Some gardeners choose to dig their tubers immediately after this first frost, but there is often a benefit to waiting. As long as the ground itself has not frozen, the tubers are safe and continue to "cure" in the cool soil.
The Hard Freeze
A hard freeze is a more significant event where temperatures drop well below freezing for several hours. This will completely turn the dahlia plant into a blackened, mushy state. While the top of the plant looks dead, the tubers underground are usually protected by several inches of soil.
You should aim to remove your tubers after the foliage has died back but before the ground freezes solid. If the soil freezes to the depth where the tubers are located, the water inside the tubers will expand and turn them to mush. Once a tuber has frozen and thawed, it is no longer viable and will quickly rot.
Key Takeaway: The ideal time to remove dahlia tubers is after the first frost has blackened the foliage but before the ground freezes solid.
Why Timing Varies by Region
Because the United States covers so many different climate zones, there is no single calendar date that works for everyone. At Longfield Gardens, our Shipping Information is based on USDA hardiness zones to ensure your order arrives at the right planting time, and the same logic applies to the end of the season.
Cold Climates (Zones 3–6)
In northern regions, the first frost often arrives in September or October. Gardeners in these areas need to be proactive. Because the ground can freeze quite early, you should watch the forecast closely. Once that first hard frost hits and turns the plants black, you generally have a window of one to two weeks to get the tubers out of the ground safely.
Moderate Climates (Zone 7)
In Zone 7, the timing is often mid-to-late November. In some years, a true killing frost might not arrive until December. Gardeners here have more flexibility. However, fall rains can be a factor. If your soil stays very wet during the autumn, it may be better to remove the tubers a bit earlier to prevent rot, even if a hard frost hasn't occurred yet.
Warm Climates (Zones 8–11)
In these southern and coastal regions, the ground rarely freezes deep enough to kill a dahlia. Many gardeners in these zones choose to leave their dahlias in the ground year-round. If you decide to do this, we recommend cutting the stalks back and covering the area with a thick layer of mulch to keep the tubers dry and protected from occasional cold snaps. However, even in warm zones, it is a good idea to lift and divide the clumps every two or three years to prevent overcrowding and maintain plant health.
The Two-Week Rule
Many experienced dahlia growers follow the "two-week rule." This means waiting approximately 10 to 14 days after the foliage has been killed by frost before digging. There are two main reasons for this wait:
- Skin Toughening: During this period, the skin of the tuber thickens and hardens. This "curing" process makes the tuber more resistant to mechanical damage during digging and better at retaining moisture during winter storage.
- Eye Development: The "eyes" of the dahlia are the small buds located on the crown from which next year's stems will grow. These eyes often become more prominent and easier to see after the plant has been dormant for a week or two. If you plan to divide your tubers in the fall, having visible eyes makes the job much easier.
If your local forecast predicts a deep, ground-penetrating freeze immediately after the first frost, you should skip the two-week wait and lift them sooner. Safety of the tuber is always the priority.
What to Do Next
- Check your local 10-day weather forecast daily starting in late September.
- Identify which plants you want to keep and ensure they are clearly labeled while the flowers are still visible.
- Gather your supplies (garden forks, labels, storage containers) so you are ready to act when the frost hits.
Preparing the Plants for Removal
Once the foliage has turned black and you are ready to dig, the first step is to manage the stems. Dahlia stems are hollow, much like a straw. If you cut them down and leave them in the ground during a rainy week, water can travel down the hollow stem and sit in the crown of the tuber clump. This can lead to "crown rot," which is a common reason for tuber loss. For more support tips, see How to Pinch and Stake Dahlias.
To prevent this, leave about 4 to 6 inches of stem attached to the clump when you cut the foliage away. This provides a "handle" for you to hold onto when you are lifting the plant, and it keeps the open end of the stem well above the soil line.
If you have a large number of plants, you can use loppers or even a hedge trimmer to clear away the bulk of the foliage. Always clean your cutting tools with a simple solution of 10% bleach or a disinfectant spray between plants. This prevents the accidental spread of soil-borne diseases from one clump to another.
How to Lift Dahlias Safely
Dahlia tubers are surprisingly fragile, especially at the "neck," which is the narrow part where the tuber body connects to the crown. If the neck is bent or cracked, the tuber will likely rot or fail to sprout next year.
Step 1: Loosen the Soil
Do not pull on the stems to get the plant out of the ground. Instead, use a garden fork or a sturdy spade. Start digging about 12 inches away from the main stem. This ensures you aren't accidentally stabbing the tubers, which grow outward from the center like the spokes of a wheel.
Step 2: Work the Perimeter
Drive your fork deep into the soil and gently pry upward. Move around the entire circle of the plant, loosening the soil on all sides. You want the entire clump to feel loose and buoyant in the soil before you attempt to lift it.
Step 3: The Gentle Lift
Once the soil is loose, slide your fork under the center of the clump and lift slowly. Use your other hand to steady the stem handle. As the clump comes out of the ground, gently shake it to remove large clods of soil.
Key Takeaway: Always dig wide and deep to avoid piercing the tubers, and never pull by the stem until the soil is completely loosened.
Post-Removal Handling
What you do in the hours immediately after removal determines how well the dahlias will store.
Cleaning the Tubers
There is some debate among gardeners about whether to wash tubers. If you have sandy soil that falls away easily, you might not need to wash them at all. However, if you have heavy clay soil, it can harbor moisture and bacteria that lead to rot.
If you choose to wash them, use a gentle spray from a garden hose. Avoid high-pressure nozzles that can nick the skin. Once washed, turn the clumps upside down. This allows any water trapped in the hollow stems to drain out. Leaving water inside the stems is a primary cause of rot during the first few weeks of storage.
Curing and Drying
Before they go into their final storage containers, dahlia tubers need to dry. Place them in a frost-free, shaded area with good air circulation. A garage or a covered porch works well. Let them dry for 24 to 48 hours. The goal is for the exterior skin to feel dry to the touch and for any remaining soil to be crumbly. Do not leave them in direct sunlight, as this can cause the tubers to shrivel and lose too much vital moisture.
Labeling Your Collection
It is incredibly easy to lose track of which tuber is which once the flowers are gone. Use a waterproof garden marker to write the variety name directly on the skin of the tuber. Alternatively, you can use plastic tags or flagging tape tied securely to the stem handle. If you have a favorite variety from our Dahlia Collections, making sure it is labeled now will save you a lot of guesswork in the spring.
Determining If a Tuber Is Worth Saving
As you remove your dahlias, you may find that some clumps look better than others. Not every tuber produced by the plant is a winner. Here is how to decide what to keep:
- The "Mother" Tuber: This is the original tuber you planted in the spring. It is usually darker, wrinkled, and may feel slightly soft. Most gardeners discard the mother tuber because it is prone to rotting in storage and doesn't produce as vigorously as new tubers.
- Size Matters: A viable tuber should generally be at least the size of a AA battery or your pinky finger. Very small, spindly tubers often dry out completely before spring arrives.
- Check for Damage: If you accidentally sliced a tuber with your shovel, you can still save it if the damage is clean. Simply trim away the jagged edge and let it dry thoroughly. If the neck of a tuber is broken or "floppy," it should be discarded, as it won't be able to send energy to the crown to sprout.
- Signs of Rot: If you see soft, brown, or smelly spots on a tuber, cut them away until you see clean, white flesh. If the rot has reached the crown, the entire clump may need to be thrown away to protect the rest of your collection.
Storage Conditions for Success
While the "when" of removal is our focus, where you put them afterward is the final piece of the puzzle. Once removed, cleaned, and dried, your tubers need a specific environment to survive the winter.
- Temperature: The sweet spot is between 40°F and 50°F. If it’s too cold (below 35°F), they may freeze. If it’s too warm (above 55°F), they may start to sprout prematurely or shrivel from moisture loss.
- Humidity: You want a middle ground. We suggest storing tubers in a medium that holds a tiny bit of moisture but stays breathable. Popular choices include slightly damp peat moss, vermiculite, or wood shavings (the kind used for animal bedding).
- Containers: Cardboard boxes, plastic bins with the lids left cracked, or burlap bags all work well. Avoid airtight plastic bags, as these trap moisture and lead to mold.
What to Do Next
- Prepare your storage medium (peat moss or shavings) a few days before you plan to dig.
- Find a spot in your basement or crawlspace that stays consistently cool.
- Set a reminder on your calendar to check the tubers once a month during the winter to ensure they aren't rotting or drying out.
Variations in Tuber Production
When you remove your dahlias, you might be surprised to find that different varieties produce different types of tubers. Some varieties are "generous" and will produce a massive clump of 10 to 15 fat tubers. Others are more "stingy," producing only two or three small tubers.
This variation is completely normal and is often tied to the specific genetics of the variety. For example, many of the giant big-blooming dinnerplate dahlias put so much energy into their massive blooms that they have less energy left for tuber production. Conversely, many smaller pompon dahlias are prolific tuber makers.
The soil quality also plays a role. If your soil is very compacted or lacks nutrients, the tubers may be smaller. This is why we emphasize the importance of timing; giving the plant every possible day of growth in the fall helps maximize whatever tuber potential that specific variety has.
Safety and Toxicity
When removing and handling dahlia tubers, it is important to remember that they are considered toxic to dogs, cats, and horses if ingested. While they aren't usually fatal, they can cause skin irritation or digestive upset.
When you are digging and cleaning your tubers, keep your pets away from the garden beds and the cleaning area. If you have a dog that loves to "help" you dig, be especially careful that they don't mistake a tuber for a toy. Once the tubers are in storage, ensure the containers are kept in a location where curious pets cannot reach them.
Summary of the Removal Timeline
Understanding the sequence of events helps take the stress out of the process. Gardening is a rhythmic activity, and the end of the dahlia season is simply the beginning of the next year's cycle.
- Late Summer: Label your plants while they are in bloom.
- First Frost: Foliage turns black. The "wait" begins.
- 10–14 Days Later: Skin toughens and eyes may become visible.
- The Big Day: Cut stems to 4–6 inches, dig wide, and lift gently.
- 48 Hours Later: Tubers are clean, dry, and labeled.
- Winter: Tubers are tucked away in a cool, dark, frost-free spot.
Conclusion
Success with dahlias is largely about working with nature’s cues rather than fighting against them. By waiting for the first frost and allowing the tubers a short window to mature in the ground, you are giving your plants the best possible start for the following year. At Longfield Gardens, we take pride in providing high-quality tubers that are ready to perform, backed by our 100% Quality Guarantee, and with a little care during the removal process, you can keep those same varieties blooming in your garden for many seasons to come.
Key Takeaway: Patience is the secret to dahlia storage; letting the plant tell you when it is ready results in healthier, more resilient tubers.
We encourage you to experiment with different varieties and enjoy the process of building your collection. Each year you save your tubers, you become more in tune with the unique needs of your garden's microclimate. For more help with your flower garden, feel free to explore our All About Dahlias guide and variety spotlights.
FAQ
Can I remove dahlia tubers before the first frost?
Yes, you can remove them earlier if you have a short growing season or if heavy fall rains are threatening to rot the tubers. However, tubers dug before a frost may be smaller and have thinner skins, so they will require extra care and closer monitoring during winter storage to prevent shriveling.
What happens if I leave the tubers in the ground through a freeze?
If only the top of the soil freezes, the tubers might survive. However, if the ground freezes several inches deep, the cells within the tubers will rupture. Once the ground thaws, the tubers will turn into a soft, rotten mess. It is always better to dig a week too early than a day too late.
Do I have to wash the soil off the tubers before storing them?
Washing is not strictly required, but it is highly recommended if you have heavy or diseased soil. Removing the soil allows you to inspect the tubers for damage or rot and ensures you aren't bringing pests or fungal spores into your storage area. If you don't wash them, at least ensure the soil is completely dry before packing them away.
How do I know if the "eyes" are present?
The eyes look like tiny, raised bumps or "pimples" located on the crown (the area where the tuber meets the stem). They can be very hard to see immediately after digging. Waiting 10–14 days after the frost before digging often causes these eyes to swell slightly, making them much easier to identify for gardeners who want to divide their clumps in the fall.
