Introduction
There is nothing quite like the late-summer garden when dahlias are in full swing. From the massive, velvety petals of dinnerplate varieties like Kelvin Floodlight to the perfectly geometric shapes of pompon types, these flowers are the undisputed stars of the autumn landscape. At Longfield Gardens, we believe every gardener should experience the joy of harvesting a fresh bouquet of dahlias from their own backyard.
However, as the nights grow crisp and the first frost approaches, many gardeners find themselves asking the same question about dinnerplate dahlias: do you actually need to dig up those tubers, or can they stay in the ground? The answer depends on a few specific factors, primarily your local climate and your soil conditions.
This guide will help you determine the best winter plan for your dahlias, whether you live in a chilly northern state or a mild southern one. We will cover how to identify your "winter strategy," the benefits of lifting tubers, and the simple steps to ensure your plants return even more vigorously next year. Understanding these basics makes dahlia care a rewarding part of your gardening rhythm rather than a mystery.
Understanding Your Hardiness Zone
The most important factor in deciding whether to dig up your dahlia tubers is your USDA plant hardiness zone. Dahlias are tropical plants native to the high plains of Mexico. They love the sun and warm soil, but they are not built to survive freezing temperatures. In the gardening world, we describe them as "tender perennials."
If you live in USDA zones 8 through 11, you are in luck. In these warmer regions, the ground rarely freezes deep enough to reach the tubers. Many gardeners in these areas successfully leave their dahlias in the ground year-round. A thick layer of mulch is usually all that is needed to keep them cozy until spring.
If you live in USDA zones 7 or colder, the situation is different. In these regions, winter temperatures regularly drop far below freezing. If the soil freezes at the depth where the tubers are buried, the water inside the tuber cells will expand, causing the cell walls to burst. This leads to a mushy, rotten tuber that will not grow in the spring. For gardeners in these cooler zones, digging up and storing the tubers indoors is the best way to enjoy the same plants year after year.
Key Takeaway: If you live in Zone 7 or colder, plan to dig up your tubers after the first frost to keep them safe. If you are in Zone 8 or warmer, you can likely leave them in the ground with proper protection.
The Role of Soil Drainage
Even if you live in a warm climate, your soil type and drainage play a major role in whether your dahlias survive the winter. Dahlias have a complicated relationship with water. While they need plenty of moisture during the heat of the summer to produce those spectacular blooms, they prefer to be relatively dry during their dormant winter phase.
"Drainage" is a term gardeners use to describe how fast water leaves the soil. If you have "heavy" soil, such as clay, it tends to hold onto water like a sponge. In the winter, cold and soggy soil is the primary enemy of dahlia tubers. Even if it doesn't freeze, a tuber sitting in wet, cold clay for three months will almost certainly rot.
If your garden has sandy soil or well-amended loam that drains quickly, your tubers have a much better chance of surviving. Before deciding to leave your tubers in the ground, consider how your garden bed behaves during a winter rainstorm. If water puddles on the surface and stays there, it is much safer to lift the tubers and store them in a controlled environment.
Why Digging Up Tubers Is Often Better
Even if you live in a region where dahlias could survive the winter in the ground, there are several reasons why you might choose to dig them up anyway. Lifting tubers isn't just about protection from the cold; it’s about the long-term health and productivity of your plants.
Preventing Overcrowding
A single dahlia tuber planted in May will grow into a large "clump" of tubers by October. This is one of the most exciting things about growing dahlias—they multiply! If you leave that clump in the ground for several years, it will eventually become too large. The tubers will compete with each other for nutrients and space, leading to smaller flowers and weaker stems. Digging them up allows you to divide the clump, which keeps the plants vigorous.
Increasing Your Collection
When you dig and divide your tubers, you essentially get free plants. A single Penhill Watermelon dahlia clump might yield five or six viable tubers for the following year. By lifting them, you can separate these and expand your garden or share the extras with friends and neighbors.
Inspecting for Health
Lifting your tubers gives you a chance to play "garden detective." You can check for signs of pests or rot that might be hidden underground. It is much easier to discard one unhealthy tuber in the fall than to wonder why a plant fails to emerge in the spring.
What to Do Next: Assessing Your Spot
- Check your USDA zone to see if your winters are typically "safe" for dahlias.
- Observe your soil after a heavy rain to see if it stays soggy or drains quickly.
- Decide if you want to expand your garden by dividing tubers this year.
When Is the Right Time to Dig?
Timing is everything when it comes to lifting dahlias. If you dig too early, the tubers may not have stored enough energy to last through the winter. If you wait too long, a deep freeze could damage them.
The best signal to watch for is the first killing frost. This is the night when temperatures drop just low enough to turn the dahlia foliage from bright green to black or brown. While it might look a bit sad to see your beautiful plants wither, this is actually a helpful signal. The plant is moving its energy from the leaves and stems down into the tubers for winter storage.
Many experienced gardeners wait about 10 to 14 days after the first frost before they start digging. This short waiting period allows the "eyes" on the tubers to become more visible. The "eyes" are small bumps where next year’s sprouts will emerge, similar to the eyes on a potato. Seeing these eyes makes it much easier to divide the tubers later.
If you live in a frost-free area but still want to lift your tubers for division, you can simply wait until the plants begin to yellow and die back naturally in late autumn. This usually happens as the days get shorter and the plant's life cycle comes to an end for the season.
How to Dig Up Dahlias Properly
Digging up dahlias is a straightforward process, but it requires a gentle touch. Dahlia tubers are connected to the main stem by a narrow "neck." This neck is quite fragile, and if it snaps, the tuber will usually not grow.
Step 1: Cut Back the Stems
Using sharp garden pruners or loppers, cut the dahlia stems down so only about 4 to 6 inches remains above the soil. This gives you a handle to hold onto without the bulk of the entire plant getting in your way.
Step 2: Loosen the Soil
It is best to use a garden fork rather than a shovel. Shovels have sharp edges that can easily slice through a tuber. Start your digging about 12 inches away from the main stem. This ensures you are outside the "splash zone" of the tuber clump. Gently push the fork into the soil and pry upward, working your way in a circle around the plant.
Step 3: Lift with Care
Once the soil is loose, reach down and get your hands under the clump. Lift the entire mass of tubers and soil upward. Avoid pulling on the stem like a handle, as this can put too much stress on the fragile necks of the tubers.
Step 4: Clean the Tubers
Gently shake off the excess soil. You can use your fingers or a soft brush to remove large clumps of dirt. Some gardeners prefer to wash their tubers with a garden hose to see the eyes more clearly. If you choose to wash them, make sure they have plenty of time to dry completely before you move on to storage. Moisture is the biggest cause of rot in storage, so "bone dry" is the goal.
Key Takeaway: Always use a garden fork and start a foot away from the stem to avoid accidental damage to the tubers.
Drying and Curing: The Secret to Storage
Once your tubers are out of the ground and clean, they need a short "rest" before they go into long-term storage. This process is called curing. Curing allows the outer skin of the tuber to toughen up slightly, which helps prevent it from drying out or shriveling over the winter.
Place your tubers in a cool, dry area that is protected from frost and direct sunlight. A garage, shed, or covered porch works well. Lay them out in a single layer on a piece of cardboard or a mesh tray. Let them sit for 2 to 3 days.
During this time, any remaining moisture on the surface will evaporate. If you washed your tubers, make sure you turn them over so no water stays trapped in the hollow center of the cut stems. If the stems are very large and hollow, some gardeners even tip the clumps upside down to ensure all the water drains out.
Packing Your Tubers for the Winter
After the tubers are cured, they are ready for their winter nap. The goal of storage is to keep the tubers in a "Goldilocks" environment: not too cold (freezing), not too warm (which causes them to sprout), not too wet (rot), and not too dry (shriveling).
The Ideal Storage Container
You can use cardboard boxes, plastic bins with ventilation holes, or even paper bags. Many gardeners find success using "nesting" material to surround the tubers. This material helps regulate moisture and prevents the tubers from touching each other, which stops any potential rot from spreading. Common materials include:
- Coarse vermiculite
- Peat moss
- Pine sawdust or wood shavings
- Dry compost
Packing Technique
Place a layer of your packing material in the bottom of the container. Lay the tubers on top, ensuring they aren't crowded. Cover them with more material until they are completely tucked in. If you are storing several different varieties, like the deep red Rip City, be sure to label them now.
The peach-toned David Howard tubers all look very similar once they are out of the ground, so you can write the variety name directly on the skin of the tuber with a soft pencil or a permanent marker.
Finding the Best Location
The best place to store your packed tubers is a cool, dark spot that stays between 40°F and 50°F. A basement, a crawl space, or a cool closet in an unheated garage is usually perfect. Avoid placing them near a furnace or a water heater, as the dry heat will cause the tubers to shrivel.
Dividing: Now or Later?
One of the most debated topics among dahlia lovers is whether to divide the tubers in the fall or wait until the spring. At Longfield Gardens, we see the benefits of both approaches.
Dividing in the Fall
The main advantage of dividing in the fall is that the tubers are softer and easier to cut. If you have limited storage space, dividing now also means you only have to store the viable tubers rather than large, bulky clumps. The downside is that the "eyes" can be very difficult to see immediately after digging. If you accidentally cut off the part of the tuber that contains the eye, it will never grow.
Dividing in the Spring
Many gardeners prefer to store the entire clump and divide it in March or April. By springtime, the tubers will naturally begin to wake up, and the eyes will swell and turn pink or white. This makes it very easy to see exactly where to make your cuts. The tubers will be much harder and "woody" by this time, so you may need a very sharp pair of snips or even a small knife.
Regardless of when you choose to divide, the rule is the same: every viable division must have a "body" (the tuber), a "neck," and at least one "eye" located on the "crown" (the area where the tuber meets the stem).
What to Do Next: Post-Digging Checklist
- Cut stems to 6 inches after the first frost.
- Gently lift the clump with a garden fork.
- Let the tubers dry/cure in a protected spot for 2-3 days.
- Pack in a breathable container with vermiculite or peat moss.
- Store in a cool, dark place (40-50°F).
Leaving Dahlias in the Ground: A Survival Guide
If you live in Zone 8 or warmer and have decided to leave your dahlias in the ground, you still have a few simple tasks to ensure they return happily in the spring.
Mulching is Key
The goal of leaving dahlias in the ground is to keep the soil temperature stable. In late autumn, after the foliage has died back, cut the stems down to about 2 or 3 inches. Cover the entire area with a generous layer of mulch. You can use fallen leaves, straw, or wood chips. A layer 4 to 6 inches deep is usually sufficient to act as an insulating blanket against occasional cold snaps.
Moisture Management
In rainy climates, you might want to protect the hollow stems from taking in too much water. Some gardeners place a small piece of aluminum foil or a small upside-down pot over the cut stems to keep rain from falling directly into the center of the tuber clump.
Spring Cleanup
In the spring, wait until the danger of frost has passed before you pull back the mulch. Once the soil begins to warm up, you will see new green shoots pushing through the earth. This is a great time to apply a balanced fertilizer to give them a boost for the coming season.
Dealing with Common Winter Challenges
Even with the best care, gardening always involves a little bit of trial and observation. Here is how to handle a few common situations you might encounter during the winter.
Shriveling Tubers
If you check your stored tubers in January and they look like wrinkled raisins, they are getting too dry. This often happens if the storage area is too warm or the packing material is too airy. You can fix this by lightly misting the packing material with a spray bottle of water. You don't want it to be wet, just slightly damp to the touch.
Surface Mold
If you see a little bit of white fuzzy mold on the surface of a tuber, don't panic! This is often just surface mold from a lack of airflow. Simply wipe it off with a cloth and ensure your storage container has a bit more ventilation. However, if the tuber feels mushy or smells bad, it has rot. Remove any rotten tubers immediately so the rot doesn't spread to the healthy ones.
Early Sprouting
If your tubers start growing long, pale sprouts in February, your storage area is likely too warm. Move the container to a cooler spot. You don't need to break off the sprouts unless they are exceptionally long; they can usually be planted directly into the ground (or a pot) when the weather warms up.
Summary of Winter Dahlia Care
Dahlias are incredibly rewarding plants that offer a massive return on a small amount of effort. Deciding whether to dig them up is simply a matter of understanding your environment.
If you live in a cold climate or have heavy, wet soil, digging up your tubers is the safest path. It ensures your favorite varieties stay protected and gives you the opportunity to multiply your collection for free. If you are in a warm, well-drained area, a simple layer of mulch is often enough to keep the magic going year after year.
At Longfield Gardens, our goal is to make these beautiful flowers accessible to everyone. By following these simple steps for digging and storage, you can treat your dahlia tubers as a long-term investment in your garden’s beauty.
Key Takeaway: Success with dahlias comes down to temperature and moisture control. Keep them cool, dry, and frost-free, and they will reward you with a spectacular show every summer.
Conclusion
Whether you choose to lift and store your tubers or tuck them in with a thick layer of mulch, taking a little time to care for your dahlias in the fall ensures a more beautiful garden next year. These plants are remarkably resilient and generous, often giving us more than we started with.
- Know your zone: Zone 7 and below should dig; Zone 8 and above can mulch.
- Prioritize drainage: Soggy soil causes rot, even in warm weather.
- Store correctly: Aim for a cool, dark, and dry location between 40-50°F.
- Label everything: You will be glad you did when planting time arrives in spring!
The process of digging and storing dahlias is a wonderful way to stay connected to your garden even during the quiet winter months. We invite you to explore our selection of premium dahlia collections at Longfield Gardens to find the perfect colors and shapes for your next growing season. Happy gardening!
FAQ
How do I know if my dahlia tuber is still alive?
A healthy tuber should feel firm to the touch, similar to a fresh potato. If the tuber is shriveled but still firm, it is likely alive but needs a little moisture. If the tuber is mushy, soft, or has a foul odor, it has rotted and should be discarded. You should also look for an "eye" near the top of the tuber; if the eye is present and the tuber is firm, it is ready to grow.
Can I leave dahlias in pots over the winter?
Yes, if you grow dahlias in containers, you can move the entire pot into a frost-free area like a garage or basement. Cut the foliage back after the first frost and stop watering. The soil in the pot will act as insulation for the tubers. In the spring, you can either refresh the top few inches of soil and start watering again, or dig up the tubers to divide them and give them fresh soil.
What happens if I forget to dig up my dahlias in Zone 5 or 6?
In these colder zones, the ground freezes deep enough to reach the tubers. If left unprotected, the tubers will freeze, turn to mush, and die. While there are occasional stories of dahlias surviving in "microclimates" (like right next to a warm house foundation), it is much safer to dig them up if you want to ensure they return.
Do I have to wash the dirt off the tubers before storing them?
It is not strictly necessary to wash them, and some gardeners prefer to leave a little bit of dry soil on the tubers as it can provide an extra layer of protection. However, washing them makes it much easier to see the "eyes" and identify any signs of rot or damage. If you do wash them, the most important rule is to make sure they are completely dry before you pack them away for the winter.
