Table of Contents
- Introduction
- Understanding Your Climate and USDA Zone
- Why Some Gardeners Dig Even in Warm Climates
- The Right Timing: When to Start Digging
- Step-by-Step: How to Dig Up Your Dahlias
- Cleaning and Curing the Tubers
- Identifying the Anatomy of a Tuber
- Successful Storage Strategies
- Mid-Winter Maintenance
- Planning for Spring
- Realistic Expectations for Overwintering
- Conclusion
- FAQ
Introduction
There is nothing quite like the late-summer magic of a dahlia garden in full bloom. From the massive, pillowy petals of dinnerplate varieties to the perfectly symmetrical pompons, these plants are the undisputed stars of the autumn landscape. As the season begins to wind down and the first hints of autumn chill arrive, many gardeners find themselves asking one specific question: do I dig up dahlia bulbs?
At Longfield Gardens, we want to help you enjoy these spectacular flowers year after year. Understanding how to handle your dahlia tubers—which are often called bulbs—is the secret to building a larger, more beautiful collection over time. This guide is designed for home gardeners who want clear, practical advice on overwintering their plants and preparing for next year’s display.
We will cover how to determine if your climate requires digging, the best time to start the process, and the simple steps for successful storage. By getting a few basics right, you can protect your investment and look forward to even more blooms next summer with a dahlia collection. Successful overwintering depends on your local climate, your soil conditions, and a few easy storage techniques.
Understanding Your Climate and USDA Zone
The decision of whether to dig up your dahlias usually comes down to where you live. Dahlias are native to the high plains of Mexico and Central America. In their natural habitat, they enjoy warm days and a dry dormant period. They are not naturally equipped to survive freezing temperatures or sitting in cold, soggy soil for months at a time.
In the United States, we use USDA Plant Hardiness Zones to help determine which plants can survive the winter in specific regions. Generally, dahlias are considered hardy in Zones 8 through 11. If you live in one of these warmer regions, such as parts of the Pacific Northwest, the South, or the Southwest, your dahlias may be able to stay in the ground all year.
However, if you live in Zone 7 or colder, the ground typically freezes deep enough to damage the tubers. When the water inside the tuber freezes, it expands and destroys the plant's cell walls. This results in the tuber turning into a soft, mushy mess once it thaws. If you are unsure of your zone, you can easily find it by entering your zip code on our website or checking a hardiness zone map.
Soil Drainage Matters
Even if you live in a warm Zone 8 or 9, digging may still be a good idea if your soil is heavy clay or if you experience very wet winters. "Drainage" is a term we use to describe how fast water leaves the soil. Dahlias "breathe" through their tubers during their winter rest. If they are submerged in water or sitting in mud, they are likely to rot before spring arrives.
If you have light, sandy soil that drains quickly, your dahlias have a much better chance of surviving a wet winter in the ground. If you have heavy soil that stays wet and cold, digging them up is the safest way to ensure they return.
Key Takeaway: If you live in USDA Zone 7 or colder, you should always dig up your dahlias. In Zones 8 and warmer, you can leave them in the ground if your soil drains well and doesn't stay soggy.
Why Some Gardeners Dig Even in Warm Climates
You might wonder why someone in a warm climate would bother digging if they don't have to. There are several excellent reasons to lift your tubers every year or two, even if you live in a region where they are hardy.
First, dahlias are incredibly productive. A single tuber planted in the spring will grow into a large clump by the fall. If left in the ground for several years, these clumps can become massive. Overcrowded tubers compete for nutrients and space, which can lead to smaller flowers and weaker stems over time. Digging allows you to divide the clumps, giving you free plants to put in other parts of your garden or to share with friends.
Second, digging gives you a chance to refresh your garden beds. When the tubers are out of the ground, you can easily add compost or organic matter to the soil to prepare for the next growing season. It also allows you to reorganize your garden. If you realized that a tall border dahlia variety was blocking a shorter one, digging is the perfect time to plan a better layout for next year.
Finally, lifting the tubers allows you to inspect them for health. You can remove any parts that look unhealthy or damaged, ensuring that only the strongest, best-performing plants stay in your collection.
What to do next:
- Check your USDA Hardiness Zone.
- Observe how well your garden soil drains after a heavy rain.
- Decide if you want to expand your garden by dividing your plants this year.
The Right Timing: When to Start Digging
Timing is often more important than the specific "tips" you might find online. For a broader overview, see our All About Dahlias guide. For dahlias, the plant needs to tell you when it is ready to go to sleep. We call this "dormancy," which is a period when the plant stops growing and saves its energy for the future.
The most common signal for digging dahlias is the first frost. You will notice that after a night of freezing temperatures, the once-vibrant green foliage will turn black or dark brown almost overnight. This might look disappointing, but it is a natural part of the cycle. When the top of the plant dies back, the energy from the leaves and stems moves down into the tubers.
It is helpful to wait about 10 to 14 days after the first frost before you start digging. This brief waiting period allows the tubers to "cure" slightly in the ground. The skin on the tubers will toughen up, making them less likely to be damaged during the digging and storage process.
If Frost is Late
In some years, you may not get a killing frost until very late in the season. If the weather stays mild but the days are getting short and the plants are looking tired, you can choose to "force" dormancy. Simply cut the plants back to about 6 inches above the ground and wait about 10 days before digging. This ensures you get the tubers out of the ground before the heavy winter rains or deep freezes arrive.
Key Takeaway: Wait for the first frost to turn the foliage black. Let the tubers rest in the ground for about two weeks to toughen their skins before you begin digging.
Step-by-Step: How to Dig Up Your Dahlias
Digging up dahlias is a rewarding task that connects you to the life cycle of your garden. You don't need any specialized machinery; a simple garden fork is the best tool for the job.
1. Cut Back the Foliage
Start by cutting the stems down to about 4 to 6 inches above the soil line. These short "stems" act as handles and help you keep track of where the center of the clump is located. Discard the old foliage in your compost pile, provided the plants were healthy throughout the summer.
2. Loosen the Soil
It is important to remember that dahlia tubers grow outward from the center stem, much like the spokes of a wheel. To avoid cutting into the tubers, start digging about 12 inches away from the main stem. Insert your garden fork deep into the soil and gently pry upward.
Work your way around the entire plant, loosening the soil on all sides. This "right plant, right place" philosophy extends to how we treat the roots; by giving them plenty of space during the digging process, we ensure they remain intact.
3. Lift Carefully
Once the soil is loose, use the fork to lift the entire clump from underneath while gently holding the stem handle. Avoid pulling hard on the stem itself, as the "neck" of the tuber—the part where it attaches to the stem—is very fragile. If the neck breaks, the tuber may not be able to sprout next year.
4. Remove Excess Soil
Gently shake the clump to remove large chunks of dirt. You can use your hands or a small wooden stick to poke away the soil between the tubers. Do not be too aggressive; you just want to get the bulk of the earth off so the tubers can dry.
Cleaning and Curing the Tubers
Once the tubers are out of the ground, they need a little bit of cleaning and a short period of drying before they go into long-term storage.
Some gardeners prefer to wash their tubers with a garden hose to remove all the soil. This makes it much easier to see the "eyes" if you plan to divide them right away. However, if your soil is sandy and falls away easily, a simple brushing might be enough. If you do wash them, be sure to do it gently. A high-pressure blast of water can tear the skin or snap off small tubers.
The Drying Process
After cleaning, the tubers need to dry out. This is called "curing." Find a cool, dry place that is protected from direct sunlight and frost, such as a garage, shed, or a covered porch. Lay the tubers out in a single layer.
Many gardeners find it helpful to turn the clumps upside down so that any water trapped in the hollow stems can drain out. Trapped water in the stems is a common cause of rot during the winter. Let them dry for 1 to 3 days. The goal is for the outside of the tuber to feel dry to the touch, but you don't want them to stay out so long that they begin to shrivel or look like raisins.
Key Takeaway: Gently wash or brush off the soil and let the tubers dry in a protected area for a few days. Always store them upside down initially to drain the stems.
Identifying the Anatomy of a Tuber
Before you decide whether to divide your dahlias or store them whole, it helps to understand what you are looking at. For a closer look at tuber anatomy, see Dahlia Tubers: What You Need to Know. A viable dahlia tuber—one that will actually grow a plant—must have three specific parts:
- The Body: This is the fat, swollen part of the root that stores energy and nutrients.
- The Neck: This is the narrow part that connects the body to the main stem.
- The Crown and Eye: The crown is the area where the neck meets the old stem. The "eye" is a tiny bump on the crown that will become next year’s sprout.
If a tuber breaks off and loses its piece of the crown, it will not grow. Think of it like a potato; a slice of potato will only grow if it has an "eye." Similarly, a dahlia tuber without an eye is just a root with no way to produce a new plant.
To Divide or Not to Divide?
You have two choices: store the entire clump as it is, or divide it into individual tubers now.
Storing the whole clump is much easier for beginners. It takes up more space, but it protects the fragile necks of the tubers. You can then divide them in the spring when the "eyes" are much easier to see because they start to swell and turn pink.
Dividing in the fall saves space and allows you to fit more tubers into a smaller container. However, the eyes can be very difficult to find in the fall. If you aren't sure where the eyes are, we recommend waiting until spring to do your dividing.
What to do next:
- Inspect your clumps for the "neck, crown, and body" structure.
- Decide if you have enough storage space for whole clumps.
- Label your tubers immediately with a waterproof marker so you don't forget which variety is which!
Successful Storage Strategies
The goal of storage is to keep the tubers in a "Goldilocks" state: not too cold, not too warm, not too wet, and not too dry. We want them to stay dormant and plump until it is time to plant again in the spring.
The Ideal Environment
The perfect temperature for storing dahlia bulbs is between 40°F and 50°F. A cool basement, a crawl space, or an insulated garage often works well. If the temperature stays above 55°F, the tubers may think it is spring and start to sprout too early. If the temperature drops below freezing, they will turn to mush.
Humidity is the other key factor. Ideally, you want about 80% to 90% humidity. Since most homes are much drier than this in the winter, we use "storage mediums" to help hold moisture around the tubers.
Common Storage Mediums
You can use several different materials to pack your tubers. The goal of these materials is to provide a buffer against temperature changes and to prevent the tubers from drying out.
- Vermiculite: This is a lightweight mineral that is excellent at regulating moisture. It is a favorite among many experienced dahlia growers.
- Peat Moss: This is widely available and works well, but it can be a bit dusty to work with.
- Wood Shavings: The kind used for animal bedding (like pine or cedar) is inexpensive and provides good insulation.
- Newspaper: Wrapping individual tubers in several layers of newspaper can also work if your storage area has naturally good humidity.
The Packing Process
Place a layer of your chosen medium in the bottom of a cardboard box or a plastic bin. If using a plastic bin, do not put the lid on tightly; the tubers need a little bit of air circulation to prevent mold. Lay the tubers or clumps in the container so they are not touching each other, then cover them with more packing material.
Key Takeaway: Store tubers in a cool (40–50°F), dark place packed in vermiculite, peat moss, or wood shavings to keep them from shriveling.
Mid-Winter Maintenance
Gardening is often about observation, and that doesn't stop just because it is winter. It is a good idea to check on your stored tubers about once a month.
When you check them, look for two things: shriveling and rot.
If the tubers look very wrinkled and feel light, they are drying out. You can lightly mist the packing material with a spray bottle of water to add a bit of moisture. Be careful not to make it soaking wet; you just want to dampen the environment slightly.
If you see any soft spots, fuzzy mold, or a bad smell, that is rot. Use a clean pair of garden snips to cut away the affected part and throw it in the trash. Removing a single rotting tuber can save the rest of the box from getting infected.
Planning for Spring
As the days get longer in late winter, you might notice your tubers starting to wake up. Small pink or white bumps (the eyes) will begin to appear on the crowns. This is an exciting sign that your dahlias are ready for another year of growth.
In early spring, usually about 4 to 6 weeks before your last frost date, you can bring the tubers out of storage and into a warmer area to "pre-sprout" them if you like. If you want a refresher on spring planting, see How to Plant Dahlias. This gives them a head start, though it is not strictly necessary.
Most gardeners wait until the soil has warmed up to about 60°F before planting them back in the garden. Planting too early into cold, wet spring soil can cause the tubers to rot before they have a chance to grow. Patience during this time is always worthwhile.
Realistic Expectations for Overwintering
It is important to remember that even with the best care, not every single tuber will survive the winter. Professional growers often expect a small percentage of loss due to natural variations in the plants or unexpected weather shifts.
Some varieties are simply "better keepers" than others. You might find that your favorite dark red dahlia stores perfectly every year, while a delicate peach variety is more prone to shriveling. This is not a failure on your part; it is just the nature of working with living things. By starting with more tubers than you think you need, you ensure a full and vibrant garden every summer.
Conclusion
Deciding whether to dig up your dahlia bulbs is a simple choice based on your local climate and your goals for your garden. For those of us in colder zones, the small effort of lifting and storing tubers in the fall is a small price to pay for the incredible beauty these plants provide. For those in warmer regions, a thick layer of mulch and good drainage may be all you need to keep the magic alive.
At Longfield Gardens, we believe that gardening should be an achievable and rewarding experience for everyone. By following these straightforward steps, you can turn a single season of dahlias into a lifelong passion.
- Check your zone to decide if digging is necessary.
- Wait for the first frost before starting the process.
- Store your tubers in a cool, dry place with a moisture-regulating medium.
- Check your tubers monthly to ensure they stay healthy.
"Overwintering dahlias is one of the most satisfying ways to see your garden grow and evolve year after year."
We encourage you to take that first step this autumn. Whether you are storing one special plant or a whole border of color, the rewards of seeing those first green sprouts in the spring make every bit of effort worthwhile.
FAQ
Can I leave my dahlias in the ground if I use a lot of mulch?
If you live in Zone 7, you might be able to leave dahlias in the ground with a very thick layer (6–12 inches) of mulch and a waterproof cover, but it is a risk. The mulch helps keep the ground from freezing, but it doesn't protect against rot if the winter is very wet. For most gardeners in cold climates, digging is the only way to be 100% sure the plants survive.
What is the best temperature for storing dahlia tubers?
The ideal temperature range is between 40°F and 50°F. This is cool enough to keep the plant in a state of rest (dormancy) but warm enough to prevent the water inside the tuber from freezing. Avoid storing them near a furnace or in a spot that gets direct sunlight, as the heat will cause them to shrivel or sprout too early.
Do I have to wash the dirt off before storing them?
No, washing is not strictly necessary unless you have very heavy clay soil that is difficult to remove. In fact, leaving a little bit of dry soil on the tubers can sometimes act as a natural insulator. However, washing makes it much easier to inspect the tubers for damage and to find the "eyes" if you plan to divide the clump.
Why did my dahlia tubers turn to mush in storage?
Mushy tubers are usually a result of either freezing or rot caused by too much moisture. If the storage area dropped below 32°F, the tubers froze and "melted" when they warmed up. If the area wasn't that cold, the tubers were likely too wet when they were packed, or the storage container didn't have enough air circulation, leading to fungal rot.