Introduction
As autumn settles in and the vibrant colors of your dahlias reach their peak, it is natural to feel a bit protective of these stunning plants. There is nothing quite like the sight of a Cafe au Lait or 'Thomas Edison' dahlia blooming in the late September sun. At Longfield Gardens, we know that these flowers are often the highlight of the garden, and we want to help you enjoy them for years to come.
Deciding whether to dig up your dahlias is one of the most common questions for home gardeners as the first frost approaches. The answer depends on your local climate, your soil type, and how much time you have for garden chores. This guide is designed to help you make the best choice for your specific yard so you can feel confident and successful.
By understanding the needs of your tubers, you can ensure they stay healthy and ready to grow again next spring. Whether you live in a chilly northern state or a mild southern region, there is a simple path to keeping your dahlias thriving. The right choice is the one that balances the needs of the plant with the reality of your local winter weather, and that is just as true for a standout variety like Thomas Edison.
Understanding Your USDA Hardiness Zone
To answer the question of whether you should dig up your dahlia tubers, you must first look at your USDA hardiness zone. Hardiness Zone Map Dahlias are native to the warm, high-altitude regions of Mexico. This means they are tropical plants that do not naturally have a way to survive deep, freezing ground.
Generally, dahlias are considered hardy in USDA zones 8 through 11. In these warmer areas, the ground rarely freezes deep enough to reach the tubers. If you live in zone 8 or higher, you can often leave your tubers in the ground all winter with just a bit of extra mulch for protection.
If you live in zones 3 through 7, the winter temperatures will usually drop low enough to freeze the soil several inches deep. When dahlia tubers freeze, the water inside their cells expands and breaks the cell walls. This turns the once-firm tuber into a soft, mushy mess that cannot grow. For gardeners in these cooler zones, digging and storing the tubers indoors is the most reliable way to save your favorite varieties.
Why You Might Choose to Dig Your Tubers
Even if you live in a region where the ground doesn't freeze solid, there are several excellent reasons to dig up your tubers every year. Many experienced gardeners find that this extra step leads to a more beautiful and productive garden in the long run.
Preventing Rot in Wet Soil
While freezing is the biggest threat to dahlias, moisture is a close second. If your winter weather involves a lot of rain or heavy, wet snow, the soil can become waterlogged. Dahlias are prone to rotting if they sit in cold, soggy ground for months at a time. By digging them up and storing them in a controlled, dry environment, you eliminate the risk of losing your plants to rot. This is especially important for gardeners with heavy clay soil, which holds onto water much longer than sandy soil.
Dividing for More Flowers
Dahlia tubers are incredibly productive. A single tuber planted in the spring will often grow into a large clump of five to twenty tubers by the end of the season. If you leave these clumps in the ground year after year, they can become overcrowded. Overcrowded dahlias often produce smaller flowers and weaker stems because the plants are competing with themselves for nutrients.
Digging up the tubers allows you to divide the clumps. This not only keeps the plants healthy but also gives you "free" plants to expand your garden or share with friends. It is a rewarding feeling to turn one Cornel dahlia into five separate plants for the following year.
Keeping Your Garden Organized
Dahlias come in so many shapes and colors that it is easy to lose track of which variety is planted where. When you dig your tubers, you have the opportunity to label them clearly. This makes planning your spring garden much easier. You can move your taller varieties to the back of the border and place shorter, bedding dahlias in the front without any guesswork.
Key Takeaway: Digging up dahlias is the best way to protect them from freezing, prevent rot in wet soil, and give you the chance to divide and multiply your collection.
Reasons to Leave Your Dahlias in the Ground
For some gardeners, leaving dahlias in the soil is a perfectly valid and successful strategy. If you live in a borderline zone or simply want to experiment, there are a few scenarios where staying in the ground makes sense.
Success in Warm and Dry Climates
If you are in zone 8 or warmer and your soil has excellent drainage, your dahlias may actually prefer to stay put. Some varieties, such as Cornel Bronze or 'Ivanetti,' are known for being particularly robust. When left in the ground, these established clumps can sometimes emerge earlier in the spring and grow faster than those that were stored in a garage or basement.
The "Heavy Mulch" Method
If you live in zone 7, you are right on the edge of dahlia hardiness. Many gardeners in this zone have success leaving tubers in the ground by applying a thick layer of mulch. A "blanket" of 6 to 12 inches of straw, wood chips, or shredded leaves can act as insulation. This helps keep the soil temperature just a few degrees warmer, which is often enough to prevent the tubers from freezing.
Saving Time and Effort
Gardening should be a joy, not a chore. If you have a large number of dahlias and digging them all feels overwhelming, you might choose to dig only your most prized or expensive varieties. You can leave the rest and see how they fare. In many cases, you might be pleasantly surprised by how many return on their own, especially if the winter is mild.
What to Do Next:
- Check your USDA hardiness zone on a local map.
- Observe your garden's drainage during a heavy rain.
- Decide which varieties are your "must-haves" for next year.
- If you decide to leave them, gather mulch materials before the first hard freeze.
The Best Time to Dig: Watching the Weather
Timing is everything when it comes to lifting dahlias. You want to give the tubers as much time as possible to mature and store energy, but you don't want to wait so long that the ground freezes.
The Frost Signal
The most common signal to start digging is the first "killing frost." This is the night when temperatures drop below 32°F, causing the green leaves and stems of the dahlia to turn black or dark brown. While it might look sad to see the foliage die back, this is actually a helpful part of the process.
When the top of the plant dies, it sends a signal to the tubers to go into dormancy. The starches and sugars from the foliage move down into the tubers, which helps them survive the winter and provides the energy they need to sprout in the spring. Most gardeners wait about 3 to 7 days after this first frost before they start digging. For a full walk-through, see How to Lift and Store Dahlia Bulbs.
Digging Before the Frost
If you live in an area where the ground turns into "slimy goo" or stays very wet after a frost, you can certainly dig earlier. You do not have to wait for a frost. Many flower farmers dig their tubers in early October while the weather is still pleasant and the soil is dry. As long as the plant has had at least 90 to 100 days of growth, the tubers will be mature enough to store successfully.
Step-by-Step Guide to Digging and Dividing
Once you have decided to dig, the process is straightforward. By following a few simple steps, you can lift your tubers safely without damaging the "necks," which are the most fragile part of the plant. For more growing basics, see 8 Tips for Growing Better Dahlias.
Step 1: Cut Back the Stalks
Use a pair of clean bypass pruners or loppers to cut the dahlia stems down. You should leave about 4 to 6 inches of the main stem sticking out of the ground. This stem acts as a convenient handle and helps you keep track of where the center of the clump is located.
Step 2: Sanitize Your Tools
To keep your garden at its healthiest, it is a good idea to dip your cutting tools in a simple solution of one part bleach to ten parts water between each plant. This prevents the spread of soil-borne diseases or viruses from one clump to another. It only takes a few seconds and is a great habit for any gardener.
Step 3: Loosen the Soil
Using a garden fork is much better than using a shovel. Shovels can easily slice through tubers, while the tines of a fork allow soil to fall through. Start your fork about 8 to 12 inches away from the main stem. Gently push the fork into the soil and lift. Work your way in a circle around the plant, loosening the soil from all sides.
Step 4: Lift the Clump
Once the soil is loose, reach down and grasp the stem handle. Lift the clump gently out of the ground. If the soil is heavy, do not pull too hard, as this can snap the tubers off the main crown. A dahlia tuber needs to stay attached to the "neck" and "crown" to grow next year, so treat them with care.
Step 5: Initial Cleaning
Give the clump a gentle shake to remove large chunks of soil. If the soil is very wet, you can leave the clump on the ground for an hour or two to let it dry slightly. This makes the remaining dirt much easier to brush off.
Key Takeaway: Use a garden fork and start a foot away from the stem to avoid damaging the tubers. Gentle handling at this stage ensures the "eyes" stay intact for spring planting.
Cleaning and Curing Your Tubers
After the tubers are out of the ground, they need a little preparation before they go into their winter home. Dahlia Tubers: What You Need to Know is a helpful guide for understanding how these storage organs work.
To Wash or Not to Wash?
There are two schools of thought on washing tubers. Some gardeners prefer to hose them off completely. This makes it much easier to see the "eyes" (the small bumps where next year's growth will start) and prevents you from bringing garden soil and bugs into your storage area.
Other gardeners prefer to leave a little soil on the tubers, believing it acts as a natural protective layer. At Longfield Gardens, we usually recommend a light washing or brushing. If you do wash them with a hose, it is vital that you let them dry thoroughly before packing them away. Moisture trapped against the skin of a tuber can lead to mold and rot.
The Curing Process
Place your cleaned tubers in a cool, dry, and shaded spot for 24 to 48 hours. A garage or a covered porch is perfect. Avoid placing them in direct sunlight, as this can cause them to shrivel. During this time, the outer skin of the tuber will toughen up slightly, which helps it hold onto its internal moisture during the long winter months.
Labeling
Do not skip this step! All dahlia tubers look very similar once they are out of the ground. Use a waterproof garden marker to write the variety name directly on the skin of the tuber. Alternatively, you can use paper tags or masking tape. Knowing which tuber is a 'Dinnerplate' variety and which is a PomPon will make your spring planting much more enjoyable.
Successful Winter Storage Methods
The goal of winter storage is to keep the tubers dormant, cool, and plump. You want to prevent two things: freezing and shriveling.
The Ideal Environment
The "sweet spot" for dahlia storage is a temperature between 40°F and 50°F.
- Too Cold: If the temperature drops below 35°F, you risk the tubers freezing.
- Too Warm: If the temperature stays above 55°F, the tubers may think it is spring and start to sprout prematurely, or they may dry out and turn into "mummy" tubers.
Unheated basements, crawl spaces, and insulated garages are usually the best spots for home gardeners.
Choosing a Storage Medium
Storing tubers in a medium helps regulate moisture. It prevents the air from sucking all the water out of the tubers while also absorbing any excess moisture that might cause rot. Popular choices include:
- Vermiculite: This is many gardeners' favorite. It is sterile, lightweight, and does an excellent job of maintaining the perfect moisture balance.
- Wood Shavings: The kind sold for pet bedding works well and is very affordable.
- Peat Moss: A classic choice, though it can be a bit dusty to work with.
- Newspaper: Wrapping individual tubers in several layers of newspaper is a simple, low-cost method.
The Storage Container
Plastic bins, cardboard boxes, or even paper grocery bags can work. If you use plastic bins, do not snap the lid on tight. Leave it slightly ajar or drill a few small holes in the sides to allow for air circulation. If the tubers "sweat" inside a sealed plastic bin, they will likely rot.
Checking Your Tubers During the Off-Season
One of the secrets to successful dahlia overwintering is not to "set it and forget it." Make a point to check on your tubers once a month.
What to Look For
When you open your storage containers, look for two things:
- Signs of Rot: If you see any tubers that have turned soft, black, or fuzzy with mold, remove them immediately. Rot can spread from one tuber to the whole box if left unchecked.
- Signs of Shriveling: If the tubers look like wrinkled raisins, they are losing too much moisture. You can lightly mist the storage medium with a spray bottle of water to add a touch of humidity. You don't want them wet—just slightly less dry.
Staying Positive
It is normal to lose a few tubers over the winter. Even professional growers expect a small percentage of loss. If you find a few that didn't make it, don't be discouraged! Focus on the ones that are still firm and healthy. Each healthy tuber is a promise of a beautiful bloom in the coming summer.
Conclusion
Deciding whether to dig up your dahlia tubers is a personal choice that depends largely on where you live. For most of us in the United States, digging is a simple insurance policy that protects our garden investment. It ensures that our favorite flowers return year after year, bigger and better than before.
Whether you choose to leave your dahlias in the ground under a thick blanket of mulch or tuck them into a bed of vermiculite in your basement, the goal is the same: a successful start to the next growing season. Gardening is a journey of discovery, and learning how your dahlias respond to your local climate is part of the fun.
Our team at Longfield Gardens is here to support you every step of the way with high-quality tubers and practical advice, backed by our 100% Quality Guarantee. We believe that everyone can grow a stunning garden, and with a few basic steps, your dahlias will be the stars of the show again next year.
- Identify your USDA zone to determine your risk level.
- Wait for a frost signal or choose a dry day in October to dig.
- Store tubers in a cool, dark place between 40°F and 50°F.
- Check your stored tubers once a month to ensure they stay plump.
"The small effort of saving a dahlia tuber in the fall is rewarded tenfold when the first massive bloom opens in the heat of August."
Now that you know how to handle your tubers, the next exciting step is dreaming about your garden layout for next spring. Happy gardening!
FAQ
Can I leave dahlias in the ground in Zone 7?
In Zone 7, leaving dahlias in the ground is a bit of a gamble, but it can be successful with the right approach. If you have well-draining soil and apply a very thick layer of mulch (about 8–12 inches) before the first hard freeze, many tubers will survive. However, for your most prized varieties, digging and storing them indoors remains the safest option to ensure they return.
What happens if I don't dig up my dahlias in a cold climate?
If you live in a cold climate (Zone 6 or lower) and leave your dahlias in the ground without significant protection, the tubers will likely freeze and die. Once the ground freezes solid at the depth of the tubers, the cells inside the plant break down, causing the tubers to turn into a soft, rotten mass. This means they will not be able to grow or sprout when spring arrives.
How do I know if my dahlia tubers are still good in the spring?
Healthy dahlia tubers should feel firm to the touch, similar to a fresh potato or a carrot. If a tuber is slightly shriveled but still firm, it is usually still viable and will plump up once planted. However, if the tuber feels hollow, mushy, or completely dried out and brittle, it is no longer alive and should be discarded.
Should I wash the dirt off the tubers before storing them?
Washing the dirt off is helpful because it allows you to inspect the tubers for damage and diseases and makes it easier to see the "eyes" for dividing. However, if you choose to wash them, you must ensure they are completely dry before you pack them into storage containers. Any lingering moisture trapped in the dirt or on the skin can cause the tubers to rot during the winter.
