Introduction
There is a unique sense of excitement that comes with the first dahlia bloom of the summer. Whether it is a massive, creamy 'Café au Lait' or a bright, cheerful 'Kelvin Floodlight', these flowers bring an incredible amount of joy to the garden. Because they are so beautiful and productive, one of the most common questions we receive at Longfield Gardens is whether you need to dig up those tubers every fall.
The answer is not the same for everyone, as it depends largely on where you live and how you like to garden. This guide is for any gardener who wants to keep their favorite varieties healthy and blooming season after season. We will cover the specific conditions that require digging, how to tell if your tubers can stay in the ground, and the simple steps to store them safely if you do decide to lift them.
Knowing if you should dig up your dahlia tubers every year involves understanding your local climate and the needs of the plant.
The Short Answer: It Depends on Your Zone
In the world of gardening, we often talk about "hardiness." This refers to a plant's ability to survive the winter in a specific area. Dahlias are native to the warm high-plains of Mexico, which means they are not naturally built to survive freezing temperatures. In many parts of the United States, if you leave a dahlia tuber in the ground during a cold winter, it will freeze, turn to mush, and fail to grow the following spring.
The most reliable way to decide if you need to dig is to look at your USDA Plant Hardiness Zone.
Gardening in Zones 8 and Warmer
If you live in USDA zone 8, 9, 10, or 11, you are in a "mild" climate. In these areas, the ground rarely freezes deep enough to reach the tubers. Most gardeners in these zones can leave their dahlias in the ground year-round. A simple layer of mulch is usually enough to keep them cozy until spring.
Gardening in Zone 7 and Colder
For those in zone 7, 6, 5, or lower, the winter cold is much more intense. The frost line—which is how deep the soil freezes—will likely reach the tubers. Because dahlias are tubers (which are like potatoes with thin skins), they are mostly water. When that water freezes, it destroys the plant's cells. Therefore, in these colder zones, digging up your tubers is a necessary part of the annual garden cycle if you want to save them for next year.
Key Takeaway Most dahlias must be dug up in USDA zones 7 and colder. In zones 8 and warmer, they can usually stay in the ground with a bit of extra mulch for protection.
Why Some Gardeners Dig Even in Warm Climates
Even if you live in a warm area where the ground doesn't freeze, you might still choose to dig up your dahlia tubers. There are several practical reasons why this can be a great move for your garden’s health.
Preventing Rot in Wet Winter Soil
Dahlias hate "wet feet." While they can handle some cold, they cannot handle cold and wet at the same time. If your winters are rainy and your soil is heavy clay, the tubers may rot in the ground before spring arrives. Drainage—which is simply how fast water leaves the soil—is the most important factor here. If your soil stays soggy, lifting the tubers and storing them in a dry place is the safest bet.
Multiplying Your Collection
One of the most rewarding parts of growing dahlias is how much they grow underground. You might plant one single tuber in May, but by October, that plant has produced a large clump of 5 to 20 new tubers. If you leave them in the ground for many years, these clumps become massive and crowded. Digging them up allows you to divide the clumps, giving you many more plants to enjoy or share with friends next year.
Refreshing the Garden Layout
Gardening is a creative process, and your tastes might change from year to year. Digging up your tubers gives you the freedom to move your plants. Maybe you want your tall 'Thomas Edison' dahlias in the back of the border next year instead of the middle. Lifting the tubers makes it easy to redesign your space every spring.
Identifying the Right Time to Dig
Timing is everything when it comes to saving dahlias. If you dig them too early, the tubers may not be "mature" enough to survive storage. If you wait too long, a deep freeze might damage them.
The best signal is given by the plant itself. You should wait for the first "killing frost." This is a night when temperatures drop enough to turn the green leaves of your dahlia black or dark brown. While it might look sad to see your beautiful plant wither, this is actually a helpful part of the process.
When the foliage dies back, the plant stops sending energy to the leaves and starts sending it down into the tubers. This helps the tubers "harden off" and prepare for their dormant period. Most gardeners wait about one to two weeks after this first frost before they start digging. This short wait allows the eyes (the small bumps that will become next year's sprouts) to become more visible, which makes dividing much easier later on.
What if You Don't Get a Frost?
If you live in a very warm area but still want to dig your tubers to divide them, you can simply wait until the plant naturally begins to turn yellow and die back in late autumn. In most parts of the US, this happens by mid-November.
What to do next
- Check your USDA zone to see if digging is required.
- Keep an eye on the weather forecast for the first frost.
- Gather your tools (a garden fork and labels) before the cold hits.
- Make sure your storage containers and packing material are ready.
A Step-by-Step Guide to Digging Dahlias
Digging up tubers is a straightforward process that becomes easier with a little practice. The goal is to lift the tubers without breaking the "neck," which is the thin part where the tuber connects to the main stem.
Step 1: Cut Back the Stalks
Use a pair of sharp garden loppers or pruners to cut the main stem down to about 4 to 6 inches above the ground. This leaves you a "handle" to help lift the clump, but removes the heavy, blackened foliage that can get in the way.
Step 2: Dig Wide
It is tempting to dig right next to the stem, but dahlia tubers grow outward like the spokes of a wheel. To avoid cutting into them, start digging at least 12 inches away from the center of the plant. We recommend using a garden fork rather than a shovel. A fork is less likely to slice through a tuber and makes it easier to gently pry the clump out of the soil.
Step 3: Lift Gently
Work your way around the plant, loosening the soil on all sides. Once the soil is loose, use your fork to gently lift the entire clump from underneath. If the clump feels stuck, don't pull hard on the stem. Instead, loosen the soil a bit more until the plant comes up easily.
Step 4: Clean and Label
Gently shake off the loose soil. Some gardeners like to wash their tubers with a garden hose to see the "eyes" more clearly, while others prefer to leave a little dirt on them to help prevent them from drying out. Whichever you choose, the most important step is labeling. Dahlias all look very similar once they are out of the ground! Use a waterproof marker or a tag to identify the variety immediately.
Preparing Tubers for Winter Storage
Once your dahlias are out of the ground, they need a bit of "beauty rest" before they go into long-term storage. This process is called curing.
The Curing Process
Find a cool, dry place that is protected from the rain and wind, such as a garage or a shed. Lay your tubers out in a single layer. Let them sit for 1 to 3 days. This allows the skin of the tuber to toughen up slightly and any excess moisture to evaporate. Do not leave them in the direct sun, as this can cause them to shrivel.
Checking for Damage
Before you pack them away, take a quick look at the tubers. If you see any that are soft, mushy, or smell bad, remove them. These are signs of rot, and you don't want it to spread to your healthy tubers. If you accidentally nicked a tuber with your fork while digging, don't worry. As long as the "neck" is intact, the tuber will usually heal over and be just fine.
Choosing the Right Storage Medium
The biggest challenge with storing dahlias is finding the "Goldilocks" level of moisture. If the environment is too dry, the tubers will shrivel up like raisins. If it is too wet, they will rot. The right storage medium helps maintain that perfect balance.
Popular Storage Options
- Peat Moss: This is a classic choice because it holds a tiny bit of moisture but stays fluffy enough to allow air to circulate.
- Pine Shavings: Often sold as pet bedding, these are inexpensive and excellent for keeping tubers dry but protected.
- Vermiculite: A mineral that is great at regulating moisture levels.
- Newspaper: Some gardeners wrap individual tubers in several layers of newspaper before placing them in a box.
Selecting a Container
Avoid airtight plastic bins. Tubers are living things and they need to breathe. Cardboard boxes, wooden crates, or plastic tubs with the lids left slightly ajar are all excellent choices. Line the bottom of your container with a few inches of your chosen medium, nestle the tubers inside (making sure they aren't touching each other), and then cover them with more medium.
The Ideal Storage Environment
Where you keep your boxes matters just as much as how you pack them. You are looking for a spot that stays consistently cool but never freezes.
The ideal temperature range is between 40°F and 50°F. For many people, an unheated basement, a crawl space, or an insulated garage is perfect. If the temperature stays above 60°F, the tubers might think it is spring and try to start growing too early. If the temperature drops below 32°F, the tubers will freeze and die.
Checking In During Winter
It is a good habit to check your tubers once a month. If they look a bit shriveled, you can lightly mist the storage medium with a spray bottle of water. If you see a spot of rot on one tuber, simply cut that part off or remove that tuber entirely to keep the rest of the box healthy.
Key Takeaway Successful storage is about air, coolness, and "just right" moisture. Check your tubers monthly to ensure they stay plump and firm until spring.
To Divide or Not to Divide?
You might hear experienced dahlia growers debating whether it is better to divide the tubers in the fall or the spring. There is no wrong answer!
Dividing in the Fall
The benefit of dividing in the fall is that the tubers are soft and easy to cut. They slice almost like a potato. However, it can be harder to see the "eyes"—the tiny bumps where new growth will emerge. If you can't see the eyes, you risk cutting a tuber that won't actually grow.
Dividing in the Spring
By springtime, the eyes usually start to swell and turn pink or green, making them very easy to spot. The downside is that the tubers have toughened up over the winter and can be much harder to cut, requiring more effort and a very sharp knife.
If you are a beginner, we often recommend waiting until spring. It is much easier to see where the new life is starting, which gives you more confidence as you make your cuts.
Special Care for Container-Grown Dahlias
If you grow your dahlias in pots or raised beds, they are actually more vulnerable to cold than plants in the ground. This is because the soil in a container is surrounded by air, so it gets cold much faster than the deep earth.
If you live in a zone where you would normally leave dahlias in the ground (like zone 8), you should still consider moving your containers into a protected area like a garage. If you live in a cold zone, you must dig container dahlias every year. The freeze will move through a pot very quickly, and the tubers will not survive if left outside on a patio.
When to Start Over
Sometimes, despite our best efforts, a tuber might not make it through the winter. This is a natural part of gardening and happens to everyone from time to time. If you find your tubers have rotted or shriveled beyond saving, don't let it discourage you.
Gardening is all about the joy of the new season. At Longfield Gardens, our trial garden is always full of new varieties and old favorites, and we love the chance to try something different each year. Starting fresh with new dahlia collections is a great way to guarantee a beautiful display if your over-wintering didn't go as planned.
Summary Checklist for Dahlia Care
To make your autumn garden chores feel manageable, follow this simple sequence of events:
- Step 1: Wait for the first frost to blacken the foliage.
- Step 2: Cut stems to 6 inches and wait a few days if the weather allows.
- Step 3: Dig wide with a garden fork to lift the clumps safely.
- Step 4: Label each variety immediately.
- Step 5: Clean off the bulk of the soil and let the tubers cure for 24–48 hours.
- Step 6: Pack in a breathable container with peat moss or shavings.
- Step 7: Store in a cool, dark place (40–50°F).
Conclusion
Digging up dahlia tubers every year might seem like a big task at first, but it quickly becomes a rewarding ritual. It is the bridge between the end of one beautiful season and the excitement of the next. By taking these few simple steps, you are protecting your investment and ensuring that your garden will be filled with spectacular color year after year.
Whether you choose to leave them in the ground or tuck them away in the basement, the most important thing is to enjoy the process. Every tuber you save is a promise of beauty for the coming summer. If you ever have questions about your plants or need to refresh your dahlia collection, we at Longfield Gardens are always here to help.
"The secret to a successful garden isn't just in the planting; it's in the care we provide during the quiet months of winter."
Happy gardening, and we look forward to seeing your dahlias bloom again next year!
FAQ
How do I know if my dahlia tubers are still good in the spring?
Healthy tubers should feel firm to the touch, much like a fresh potato. If a tuber feels hollow, squishy, or brittle and dry like a cracker, it is likely not viable. Look for "eyes" or small green sprouts near the neck, which are a sure sign the tuber is ready to grow.
Can I leave my dahlias in the ground if I live in Zone 7?
It is a bit of a gamble in Zone 7. If you have a very mild winter and very well-draining soil, they might survive if you cover them with 6-12 inches of mulch. However, a typical Zone 7 winter will likely freeze the ground deep enough to kill the tubers, so digging is highly recommended to be safe. For more detail, see this guide to overwintering dahlias.
Do I have to wash the dirt off the tubers before storing them?
You don't have to wash them, but it can help you see the "eyes" and check for any hidden rot. If you do wash them, just make sure they are completely dry before you pack them away. Storing wet tubers is the fastest way to cause rot.
What happens if I forget to dig my dahlias up?
If you live in a cold climate and leave them in the ground, the tubers will likely freeze and decompose over the winter. In the spring, you won't see any new growth. If this happens, don't worry—you can simply clear the spot and shop dahlia tubers once the soil warms up.
