Table of Contents
- Introduction
- Understanding Dahlia Hardiness and Your Zone
- When You Can Safely Leave Dahlias in the Ground
- Reasons Why Many Gardeners Choose to Dig and Store
- How to Overwinter Dahlias in the Soil
- When and How to Dig Up Dahlia Tubers
- Preparing and Storing Tubers for Winter
- Conclusion
- FAQ
Introduction
Few moments in the garden are as rewarding as seeing a dinnerplate dahlia finally open its petals. These spectacular plants are the undisputed stars of the late-summer border, offering a variety of colors and shapes that few other flowers can match. At Longfield Gardens, we want to help you enjoy dahlias year after year.
Whether you need to dig up your dahlia tubers—often called bulbs—is one of the most common questions we hear. The answer depends largely on where you live and how much effort you want to put into your garden's future. For many gardeners, digging is a seasonal ritual that ensures a bigger and better display next summer. For others, a simple layer of mulch is all that is needed to keep the plants safe.
This guide will help you understand the needs of your dahlia tubers so you can decide which approach is right for your yard. We will cover the impact of your local climate, the benefits of storing tubers indoors, and the simple steps for successful overwintering. By the end, you will feel confident in your plan to keep your dahlias thriving for many seasons to come.
Your decision to dig or stay depends on a balance of climate, soil conditions, and your personal gardening goals.
Understanding Dahlia Hardiness and Your Zone
Dahlias are native to the high plains of Mexico and Central America. In their natural habitat, they enjoy warm days and cool, dry winters. Because they evolved in a frost-free environment, they are considered "tender perennials" in most parts of the United States. This means they can live for many years, but they lack the natural defenses to survive a freezing winter in the ground.
To determine if you must dig your tubers, you first need to know your USDA Plant Hardiness Zone. These zones are based on the average minimum winter temperature in your area.
- Zones 8 and Warmer: In these regions, winters are typically mild enough that dahlia tubers can stay in the ground. The soil rarely freezes deep enough to reach the tubers, allowing them to remain dormant until spring.
- Zones 7 and Colder: In these areas, the ground usually freezes several inches deep. If a dahlia tuber freezes, the cells inside the "bulb" burst, and the plant will rot when the soil thaws. For gardeners in these zones, digging up the tubers is the most reliable way to save the plant.
It is important to remember that weather is unpredictable. For a closer look at compact garden forms, our How to Grow Border Dahlias guide is a helpful companion. Even if you live in a warmer zone, an unusually cold or wet winter can still pose a risk to tubers left in the soil.
Key Takeaway: If you live in USDA Zone 7 or colder, digging up your dahlias is the best way to ensure they return next year. In Zone 8 or warmer, they can usually stay in the ground with a little extra protection.
When You Can Safely Leave Dahlias in the Ground
If you live in a mild climate, leaving your dahlias in the ground can save you time and energy. If you prefer a shorter, easier-to-place planting, browse our Border Dahlias. It also allows the plants to establish larger, more complex root systems, which can lead to earlier blooms the following summer. However, temperature isn't the only factor to consider. Soil drainage is just as important.
Drainage refers to how quickly water moves through your soil. Dahlias have thick, starchy tubers that act like storage tanks. In the winter, when the plant is dormant and not growing, it doesn't use much water. If your soil stays soggy or waterlogged during the winter months, the tubers are likely to rot, even if the temperature remains well above freezing.
You can safely leave your dahlias in the ground if:
- You live in USDA Zone 8, 9, 10, or 11.
- Your soil is sandy or loamy and does not hold onto excess water.
- The area is not in a low spot where water collects after rain or snowmelt.
Even in these warm areas, we recommend a "safety" layer of mulch. A thick layer of wood chips, shredded leaves, or straw acts like a blanket. It keeps the soil temperature stable and prevents the ground from fluctuating between freezing and thawing, which can be stressful for the tubers.
What to do next:
- Check your garden’s drainage by observing how fast puddles disappear after a heavy rain.
- If you choose to leave them, wait until the first light frost kills the top growth before applying mulch.
- Label the spot with a stake so you don't accidentally dig into them while planting spring flowers.
Reasons Why Many Gardeners Choose to Dig and Store
Even gardeners in warm climates often choose to dig up their dahlias every year. While it takes a bit more work in the fall, there are several practical benefits to this approach. Digging up your dahlias is not just about survival; it is about improving the health and beauty of your garden.
Preventing Overcrowding
A single dahlia tuber planted in the spring will grow into a large "clump" of tubers by the fall. If you leave this clump in the ground year after year, it will continue to expand. Eventually, the tubers become so crowded that they begin to compete with each other for space and nutrients. Overcrowded dahlias often produce weaker stems and fewer flowers. Digging them up allows you to separate the clump into individual tubers.
Multiplying Your Collection
One of the most exciting parts of dahlia gardening is that the plants provide you with free "bonuses" every year. When you dig up a large clump, you can divide it into several smaller pieces. Each piece that has a healthy "eye" (the small bud where next year’s stem will grow) can become a whole new plant. This is a great way to fill your garden with your favorite blooms from our Ball Dahlias or share plants with friends.
Evaluating Health
When tubers are underground, you cannot see if they are being bothered by pests or if they have started to develop soft spots. Digging them up gives you a chance to inspect the tubers. You can trim away any damaged sections and ensure only the healthiest stock goes back into the garden next spring. If you prefer a simpler flower form, the Single Dahlias collection is another option to explore.
Better Layout Flexibility
Gardens change from year to year. By digging up your tubers, you aren't committed to the same layout every season. You can store them over the winter and decide in the spring exactly where you want those spectacular blooms to go. This is especially helpful if you are trying out new color combinations with the Enchantment Collection.
Key Takeaway: Digging up dahlias isn't just about avoiding frost; it’s a great opportunity to multiply your plants, prevent overcrowding, and refresh your garden layout for the next year.
How to Overwinter Dahlias in the Soil
If you have decided that your climate and soil are suitable for leaving your dahlias in the ground, a little preparation goes a long way. This process is often called "winterizing," and the goal is to keep the tubers dry and insulated.
Start by waiting for the first frost. You will know it has arrived when the lush green leaves of your dahlias suddenly turn black or dark brown. This might look sad, but it is actually a helpful signal. The frost tells the plant to move all its remaining energy down into the tubers for storage.
- Cut Back the Stems: Once the foliage has blackened, use clean garden shears to cut the stems down to about 2 to 4 inches above the soil line.
- Clear the Area: Remove the dead leaves and stems from the garden bed. This helps prevent pests and diseases from hiding near your dormant plants over the winter.
- Apply Insulation: Pile 6 to 12 inches of mulch over the top of the cut stems. Straw, evergreen boughs, or shredded bark are excellent choices. This "blanket" protects the tubers from cold snaps.
- Manage Moisture: In very rainy climates, some gardeners place a piece of plastic or a waterproof tarp over the mulched area. This prevents the tubers from getting too wet and rotting. If you do this, make sure the plastic is weighed down so it doesn't blow away.
In the spring, once the danger of frost has passed and the soil begins to warm, you can gently pull back the mulch to allow the new sprouts to find the sunlight.
When and How to Dig Up Dahlia Tubers
For those in colder zones, the digging process is a vital autumn task. Timing is everything. We recommend waiting until a killing frost has blackened the foliage. If you live in an area that doesn't get a frost until very late in the year, you can dig them up in mid-November regardless.
Waiting for that first frost is beneficial because it "cures" the tubers. It toughens the skin and signals the plant to go into deep dormancy, which helps the tubers stay fresh and firm during their months in storage.
Step 1: Cut and Wait
After the frost kills the foliage, cut the stems down to about 4 inches. Many gardeners like to wait about a week before digging. This short rest period encourages the tubers to develop "eyes" that are easier to see, which is helpful if you plan to divide them right away.
Step 2: Use the Right Tools
A garden fork is generally better than a shovel for digging dahlias. The tines of a fork are less likely to slice through the tubers. Dahlias grow outward from the center stem, so the tubers are often much wider than you might expect.
Step 3: Dig Wide and Deep
Start by inserting your fork into the soil at least 12 inches away from the main stem. Gently lift the soil all the way around the plant to loosen the root ball. Once the soil is loose, carefully lift the entire clump out of the ground.
Step 4: Handle with Care
The "neck" is the thin part of the tuber that connects to the main stem. This is the most fragile part of the plant. If the neck breaks or snaps, the tuber will likely not grow next year. Always lift the clump from underneath rather than pulling it by the stem.
What to do next:
- Use a garden fork to avoid slicing tubers.
- Start your digging circle at least 1 foot away from the stem.
- Lift the clump from below; never pull by the "handle" of the stem.
Preparing and Storing Tubers for Winter
Once your tubers are out of the ground, they need a little care before they go into storage. Proper preparation prevents rot and keeps the tubers from drying out completely. Think of this process as putting your plants into a long, comfortable nap.
Cleaning the Tubers
Gently shake off the large clumps of soil. Some gardeners prefer to wash their tubers with a garden hose to see the "eyes" more clearly, while others leave the dirt on to provide an extra layer of protection. If you do wash them, be very gentle. Avoid using high-pressure settings that could nick the skin.
Curing and Drying
Before putting dahlias away, they need to dry out slightly. Place the clumps in a protected, frost-free area with good air circulation, such as a garage or a covered porch. Let them sit for 2 to 3 days. Do not leave them in direct sunlight or in a place where they might freeze. Drying helps the skin toughen up, which prevents moisture loss during the winter.
Choosing a Storage Container
You want a container that breathes but still holds some moisture. Cardboard boxes, paper bags, or plastic crates are all good options. Avoid airtight plastic bins, as these trap moisture and lead to rot.
Packing Material
To keep the tubers from shriveling, pack them in a slightly damp medium. Common choices include:
- Peat moss
- Vermiculite
- Coarse sand
- Pine wood shavings (like the kind used for pet bedding)
Place a layer of packing material in the bottom of your container, then lay the tubers inside. Cover them completely with more material. This prevents the tubers from touching each other, which helps stop the spread of rot if one tuber goes bad.
The Ideal Storage Spot
The perfect storage spot is cool, dark, and dry. The temperature should ideally stay between 40°F and 50°F. An unheated basement, a root cellar, or a cool closet in a garage usually works well. If the area gets too warm, the tubers might try to sprout too early. If it gets too cold, they will freeze and die.
Key Takeaway: Successful storage requires a balance. You want the tubers to be cool enough to stay dormant but protected enough to stay dry and frost-free.
Conclusion
At Longfield Gardens, we believe that gardening should be a rewarding and enjoyable experience for everyone. While the question of whether you have to dig up your dahlia bulbs every year depends on your specific location, the process doesn't have to be intimidating. By understanding your hardiness zone and providing your tubers with the right winter environment—whether that is in the ground under a layer of mulch or in a cool basement—you can ensure your garden is filled with stunning blooms year after year.
Remember that gardening is an ongoing learning process. If you aren't sure about your climate, you might try leaving a few tubers in the ground while digging up others as a backup. No matter which path you choose, the effort you put in now is an investment in a beautiful, flower-filled summer. If your garden space is limited, our Can I Grow Dahlias in Pots? guide offers another way to enjoy them. For shipping timing and delivery details, see our Shipping Information.
- Check your USDA zone to decide if digging is necessary.
- If leaving tubers in the ground, ensure the soil has excellent drainage and apply thick mulch.
- If digging, handle the tubers gently to protect the fragile necks.
- Store tubers in a cool, dark, breathable container with slightly damp packing material.
"Dahlias are one of the most generous plants in the garden. A little care in the fall ensures a wealth of color and beauty in the spring."
We stand behind the quality of our plants and want you to succeed. If you have questions about your specific varieties or need help planning your next garden, our 100% Quality Guarantee page explains how we support your order.
FAQ
Can I leave my dahlias in the ground if I live in Zone 7?
While some gardeners in Zone 7 have success leaving dahlias in the ground during mild winters, it is a risk. To do this safely, you must have exceptionally well-draining soil and apply a very thick layer of mulch (at least 12 inches). Most experts recommend digging them up in Zone 7 to be 100% sure they will survive.
What happens if I forget to dig up my dahlias in a cold climate?
If the ground freezes deep enough to reach the tubers, they will most likely turn to mush and die. In the spring, you will notice the tubers are soft and foul-smelling. If this happens, the plant will not grow back, and you will need to start with new tubers for the upcoming season.
Do I need to wash the dirt off the tubers before storing them?
Washing is a personal preference. Washing makes it easier to see the "eyes" and any signs of damage or rot, but it also adds moisture that must be dried off before storage. If you choose not to wash them, simply brush off the loose soil and ensure they are dry to the touch before packing them away.
How often should I check my stored dahlia tubers?
It is a good idea to check your tubers once a month during the winter. Look for any signs of rot (soft, mushy spots) or extreme shriveling. If a tuber is rotting, remove it immediately so it doesn't infect the others. If the tubers look very shriveled and dry, you can lightly mist the packing material with water to add a tiny bit of moisture.