Table of Contents
- Introduction
- Understanding Your USDA Hardiness Zone
- When You Can Safely Leave Dahlias in the Ground
- Why Some Gardeners Choose to Dig Regardless of Zone
- Preparing Dahlias for the Winter
- How to Overwinter Dahlias in the Ground
- A Step-by-Step Guide to Digging Dahlia Tubers
- Curing and Drying Before Storage
- Finding the Best Storage Spot
- Packing Your Tubers for Winter
- To Divide Now or Later?
- Common Myths About Digging Dahlias
- Simple Steps for Spring Success
- Conclusion
- FAQ
Introduction
Dahlias are the undisputed stars of the late-summer garden. Their incredible variety of colors, shapes, and sizes provides endless joy for gardeners who love creating homegrown bouquets. Whether you are growing a giant dinnerplate variety like Kelvin Floodlight or a charming pompon type, the reward is a season filled with spectacular blooms.
As the weather cools, many gardeners wonder how to protect these beautiful plants so they return next year. At Longfield Gardens, we want to help you make this decision based on your specific climate and garden conditions. While Dahlias are perennials, they are not winter-hardy in every part of the United States.
This guide focuses on the factors that determine whether you need to lift your tubers and the best ways to keep them safe until spring. We will walk you through the simple steps to ensure your dahlia collection stays healthy and productive, whether you favor dinnerplate blooms or pompon dahlias. Determining if you need to dig your dahlia bulbs depends primarily on your USDA hardiness zone and your soil's drainage.
Understanding Your USDA Hardiness Zone
The first step in deciding whether to dig up your dahlias is knowing your USDA hardiness zone. Dahlias are native to the warm high-plains regions of Mexico and Central America. Because of their tropical origins, they do not have a natural defense against deep soil freezes.
In the United States, dahlias are generally considered hardy in zones 8 through 11. In these warmer regions, the ground rarely freezes deep enough to reach the tubers. If you live in zone 8 or warmer, you can often leave your dahlias in the ground year-round with minimal extra care.
If you live in zones 3 through 7, the winter temperatures typically drop low enough to freeze the soil several inches deep. These freezing temperatures will cause the water inside the dahlia tuber to expand, which destroys the plant’s cell walls. This results in the tuber turning into a soft, unusable mush once it thaws. In these colder zones, digging and storing the tubers indoors is the standard practice for keeping them alive.
Key Takeaway To find your zone, check a USDA Plant Hardiness Zone Map. If your zone is 7 or lower, plan to dig your dahlias. If it is 8 or higher, you may be able to leave them in the soil.
When You Can Safely Leave Dahlias in the Ground
While temperature is a major factor, it is not the only thing that affects dahlia survival. Soil moisture is just as important as the thermometer reading. Dahlias "sleep" during the winter, a state called dormancy. When a plant is dormant, it is not actively taking up water.
In zones 8 and above, dahlias often thrive when left in the ground if the soil has excellent drainage. Drainage refers to how fast water leaves the soil after rain or irrigation. If your soil is sandy or loamy, water moves away quickly. This keeps the tubers relatively dry and healthy.
However, if you have heavy clay soil that stays soggy and cold all winter, your dahlias may rot even if it never freezes. Standing water prevents the tubers from "breathing" and invites fungal issues. Even in a warm climate, if your garden bed stays wet throughout the winter, you might choose to dig your tubers to keep them from rotting.
Microclimates and Success
Sometimes, gardeners in zone 7 find success leaving dahlias in the ground. This often happens because of a "microclimate." A microclimate is a small area where the conditions are slightly different from the surrounding region. For a broader look at planting site basics, see Where Do Dahlias Grow?
Why Some Gardeners Choose to Dig Regardless of Zone
Even in warm climates where the ground never freezes, there are several reasons why you might want to dig up your dahlia tubers anyway. Gardening is often about more than just survival; it is about helping your plants perform their best. For a broader overview, read All About Dahlias.
First, dahlias are vigorous growers. Over a single growing season, one tuber can multiply into a large clump of five to twenty new tubers. If left in the ground for several years, these clumps become overcrowded. Overcrowded dahlias compete for nutrients and water, which leads to smaller flowers and weaker stems. Digging them up allows you to divide the clumps and give each new plant plenty of space.
Second, digging gives you a chance to inspect the health of your tubers. You can remove any sections that look unhealthy and ensure you are only replanting the strongest stock. This practice leads to a more beautiful and consistent garden display.
Benefits of Digging and Storing:
- Expansion: You get more plants for free by dividing the clumps.
- Organization: You can reorganize your garden layout for the following year.
- Protection: You can safeguard rare or expensive varieties from unexpected weather extremes.
- Soil Health: It gives you a chance to amend and refresh the soil in the planting area.
Preparing Dahlias for the Winter
Whether you plan to dig your tubers or leave them in the ground, the preparation process starts in the fall. You want to wait for the plant to tell you it is ready to rest. As the days get shorter and the temperatures drop, the dahlia foliage will naturally begin to turn yellow.
For most gardeners, the "first frost" is the signal to act. A light frost will turn the leaves and stems black. Do not worry; this does not mean the plant is dead. The tubers underground are perfectly safe. In fact, many gardeners wait about a week or two after the first frost before digging. This waiting period helps the tubers "cure" slightly and develop tougher skins, which helps them stay hydrated during storage. For a closer look at tuber anatomy, see Dahlia Tubers: What You Need to Know.
What to Do Next
- Watch the weather for the first frost of autumn.
- Once the foliage turns black or brown, cut the stems down.
- Leave about 4 to 6 inches of the main stem sticking out of the ground.
- If leaving them in the ground, apply a thick layer of mulch immediately.
How to Overwinter Dahlias in the Ground
If you are in a warm enough zone and have decided to leave your dahlias in the garden, a little bit of winterizing goes a long way. Think of this as putting a warm blanket over your plants to protect them from the elements.
After cutting the stems back to about 4 inches, you should cover the entire area with a thick layer of mulch. Good mulching materials include shredded bark, straw, or pine needles. Aim for a layer that is 4 to 6 inches deep. This mulch acts as insulation, keeping the soil temperature more stable and preventing the crown of the plant from being exposed to cold air.
Another helpful trick is to cover the hollow stems. Dahlia stems are like straws; if they are left open, rainwater can run down into the center of the tuber clump and cause rot. You can place a small piece of aluminum foil over the cut stem or simply ensure the mulch mound is high enough to cover the openings.
A Step-by-Step Guide to Digging Dahlia Tubers
If you live in a cold region or simply want to divide your plants, digging is a straightforward process. You do not need expensive equipment. A standard garden fork is usually better than a shovel because it is less likely to slice through the tubers.
1. Loosen the Soil
Start by digging about 12 inches away from the main stem. Dahlia tubers grow outward like the spokes of a wheel. If you dig too close, you might accidentally chop off the most important parts. Insert your garden fork deep into the soil and gently pry upward to loosen the earth. Work your way all the way around the plant.
2. Lift Carefully
Once the soil is loose, use your fork to gently lift the entire clump out of the ground. Use your hands to support the weight of the clump from underneath. Avoid pulling on the stems, as they can snap off and damage the "neck" of the tubers. The neck is the thin part where the tuber attaches to the main stem; if this breaks, the tuber may not be able to grow next year.
3. Clean the Tubers
Once the clump is out, shake it gently to remove large chunks of dirt. Some gardeners prefer to wash their tubers with a garden hose to see the "eyes" more clearly. Others prefer to let the dirt dry and simply brush it off. If you choose to wash them, be very gentle. Use a soft stream of water so you do not bruise the skin.
4. Label Everything
This is perhaps the most important step. Once the tubers are out of the ground and cleaned, they all look very similar. Use a waterproof marker to write the variety name directly on the skin of the tuber. Alternatively, you can tie a label to the stem. Keeping your varieties organized ensures your garden colors will be exactly where you want them next spring.
Curing and Drying Before Storage
You cannot move tubers directly from the damp ground into a storage container. They need a short period of "curing." This process allows excess moisture to evaporate so the tubers do not mold while they are put away for the winter.
Place your cleaned tubers in a frost-free, shaded area with good air circulation. A garage or a covered porch works well. Avoid placing them in direct sunlight, as this can cause them to shrivel too quickly. Let them sit for one to three days.
During this time, the skins will toughen up, and any remaining soil will dry out. Once the tubers feel dry to the touch but still look plump, they are ready for their winter storage. If you see any damaged or broken tubers, use a clean pair of snips to trim them off before storage. This prevents any potential rot from spreading to the healthy parts of the clump.
Finding the Best Storage Spot
The key to successful dahlia storage is finding a location that is cool, dark, and slightly humid. The goal is to keep the tubers dormant without letting them freeze or completely dry out.
The ideal temperature for dahlia storage is between 40°F and 50°F. If the temperature stays above 60°F, the tubers might think it is spring and start to sprout too early. If the temperature drops below 32°F, they will freeze. A cool basement, a crawl space, or an insulated garage are usually the best spots.
Humidity also matters. If the air is too dry, the tubers will shrivel like a prune. If the air is too damp, they will grow mold. Most gardeners find that using a storage medium helps balance this moisture perfectly.
Popular Storage Mediums:
- Vermiculite: A lightweight mineral that holds just the right amount of moisture.
- Wood Shavings: The kind used for pet bedding is inexpensive and works well.
- Peat Moss: A classic choice, though it can sometimes be a bit dusty.
- Newspaper: Wrapping individual tubers in several layers of newspaper is a simple, low-cost method.
Packing Your Tubers for Winter
When you are ready to pack your dahlias, choose a container that allows for some air exchange. Cardboard boxes, plastic crates with holes, or paper bags are excellent choices. Avoid airtight plastic bins, as these trap moisture and almost always lead to rot.
Place a layer of your chosen storage medium (like wood shavings or vermiculite) in the bottom of the container. Lay the tubers on top, making sure they are not touching each other. Covering them with another layer of the medium provides insulation and prevents moisture loss.
If you have many different varieties, you can pack them in separate bags within a larger box. Just make sure each bag is clearly labeled. We often find that checking on the tubers once a month during the winter is a great habit. If they look shriveled, you can lightly mist the storage medium with water. If you see any soft spots or mold, remove the affected tuber immediately to protect the rest.
To Divide Now or Later?
One of the most common questions we hear is whether you should divide the dahlia clumps in the fall or wait until spring. Both methods work, and the choice is really up to you.
Dividing in the fall is often easier because the tubers are softer and more pliable. It also saves space in your storage containers since you aren't storing the "mother" tuber or any dead wood from the center of the clump. However, it can be harder to see the "eyes" in the fall. The eyes are the small bumps on the crown where the new growth will emerge.
Dividing in the spring is often easier for beginners. By late March or April, the eyes will naturally start to swell and turn pink or green, making them very easy to identify. The downside is that the tubers become quite hard over the winter, so you will need a very sharp pair of garden snips or a knife to cut through them.
Key Takeaway To be viable, every divided tuber must have three things: a healthy body, an undamaged neck, and at least one "eye" on the crown.
Common Myths About Digging Dahlias
There is a lot of advice online about dahlias, and some of it can be confusing. Let's look at a few simple truths to keep your gardening experience stress-free.
First, you do not have to wait for a hard freeze to dig your tubers. While a frost helps signal dormancy, you can dig them up anytime in late autumn once the plants have been in the ground for at least 100 days. This is helpful for gardeners who want to finish their chores while the weather is still pleasant.
Second, you do not need a professional-grade refrigerator to store dahlias. While some growers use temperature-controlled coolers, millions of home gardeners have successfully stored tubers in simple cardboard boxes in their basements for decades.
Third, don't worry if you lose a few tubers during the winter. Even the most experienced gardeners expect a small percentage of loss. This is exactly why dahlias multiply so much—nature provides extras to ensure the plant continues.
Simple Steps for Spring Success
When the ground warms up in the spring—usually around the time you would plant tomatoes—it is time to bring your dahlias out of hiding. In most parts of the country, this is late April or May.
Before planting, give your tubers a quick inspection. They should feel firm, like a fresh potato. If they are slightly shriveled but still have a visible eye, they will likely be fine once they get into the moist soil. If they are mushy or completely hollow, discard them.
At Longfield Gardens, we recommend How to Plant Dahlias. Make sure the "eye" is pointing upward toward the sky. The most important rule for spring planting is to wait for the soil to reach about 60°F. If you plant too early into cold, wet soil, the tubers may rot before they have a chance to grow.
Conclusion
Deciding whether you have to dig up dahlia bulbs is a choice that depends on your specific environment. If you live in a cold climate, digging and storing them is a rewarding way to preserve your favorite varieties and expand your garden for free. If you are in a warm region with well-draining soil, you can enjoy the ease of leaving them in the ground.
Gardening should be a source of joy, not a stressful chore. Whether you choose to lift your tubers or mulch them in place, the goal is the same: a vibrant, colorful garden full of blooms to share. By following these simple steps, you can ensure your dahlias return more beautifully each year.
- Check your USDA zone to determine if your soil will freeze.
- Wait until after the first frost to cut back foliage and dig tubers.
- Store tubers in a cool, dark place using a medium like vermiculite or wood shavings, and browse our Spring-Planted Bulb Collections.
"The magic of dahlias is that they reward a small amount of winter care with an explosion of color all summer long. Protecting your tubers is a simple investment in next year's beauty."
We are here to support your gardening journey with spring-planted summer-blooming bulbs and practical advice.
Start planning your color palette today and look forward to the most spectacular dahlia season yet with Shop by Color - Spring-Planted Bulbs.
FAQ
Can I leave dahlias in the ground in Zone 7?
In Zone 7, leaving dahlias in the ground is a calculated risk. If you have very well-draining soil and apply a thick 6-inch layer of mulch, they may survive a mild winter. However, if the winter is exceptionally cold or wet, the tubers may rot or freeze, so many gardeners in this zone prefer to dig them up for safety.
What happens if I don't dig up my dahlia tubers in a cold climate?
If the ground freezes where you live and you do not dig up the tubers, they will likely die. The water inside the tuber freezes, causing the plant tissue to collapse. Once the ground thaws in the spring, the tubers will turn into a soft, rotten mush and will not produce any new growth.
How do I know if my dahlia tubers have rotted in storage?
Check your tubers monthly during the winter. A healthy tuber should feel firm, similar to a potato. If a tuber feels squishy, looks black, or has an unpleasant odor, it has rotted. You should remove any rotten tubers immediately so the decay does not spread to the healthy ones in the same container.
Do I need to water my dahlia tubers while they are in storage?
No, you should not water them like a houseplant. The goal is to keep them dormant and slightly hydrated. If the tubers look very shriveled and dry, you can lightly mist the storage medium (like the peat moss or wood shavings) with a spray bottle, but the tubers themselves should never be sitting in wet material.