Table of Contents
- Introduction
- Why Preserving Dahlia Tubers Is Worth the Effort
- Timing Your Harvest Correctly
- Preparing to Dig Your Tubers
- The Lifting Process: How to Dig Without Damage
- Cleaning and Drying Your Dahlias
- To Divide Now or Later?
- Selecting the Right Storage Medium
- Creating the Ideal Storage Environment
- Overwintering Care: The Monthly Check-up
- Preparing for Spring: Waking the Tubers Up
- Safety and Practical Considerations
- Conclusion
- FAQ
Introduction
There is nothing quite like the late-summer garden when dahlias are in full swing. These spectacular bloomers offer a final, vibrant firework display of color just as other plants begin to fade. From the massive, plate-sized petals of dinnerplate varieties to the intricate, geometric shapes of PomPon dahlias, dahlias are the rewarding stars of many backyard landscapes.
At Longfield Gardens, we want to help you keep that beauty coming back year after year. While dahlias are tender perennials that cannot survive freezing winters in most of the United States, their tubers are easy to save if you know the right steps. This guide is for any gardener who wants to transition their favorite varieties from the garden bed to safe winter storage, and grow your dahlia collection without starting from scratch each spring.
Whether you are a first-time grower or a seasoned flower enthusiast, preserving your tubers is a practical way to grow your collection without starting from scratch each spring. By understanding the simple needs of a dormant tuber, you can ensure your garden stays colorful for many seasons to come. Our goal is to make the preservation process feel like a rewarding end-of-season ritual rather than a complicated task.
Why Preserving Dahlia Tubers Is Worth the Effort
Dahlias are native to the high plains of Mexico and Central America. In their natural habitat, the ground never freezes, and the soil stays relatively dry during the dormant season. Because most of the United States experiences freezing temperatures or heavy winter moisture, dahlia tubers will turn to mush if left in the ground in USDA zones 7 and colder. If you're not sure of your zone, see our Hardiness Zone Map.
Preserving these tubers is essentially an act of "overwintering." You are providing the plant with a controlled environment that mimics its natural dormant period. This allows the plant to rest, store energy, and prepare for a vigorous comeback when the soil warms up in the spring.
Beyond simply saving money, preserving your bulbs allows you to grow your garden exponentially. A single dahlia tuber planted in May will often grow into a large clump of five to ten tubers by October. By lifting and storing these clumps, you can divide them and turn one plant into a whole row of flowers for the following year. It is one of the most satisfying "magic tricks" in the gardening world.
Timing Your Harvest Correctly
The most common question gardeners ask is when exactly to start digging. Timing is the most important factor in ensuring the tubers have enough stored energy to survive the winter and sprout in the spring.
The Significance of the First Frost
In most regions, the signal to begin the preservation process is the first killing frost. You will know it has happened when the lush green foliage of your dahlias turns black or dark brown overnight. This might look like a sad end to the season, but it is actually a vital part of the plant’s lifecycle.
When the top growth dies back, the plant realizes the growing season is over. It quickly shifts its remaining energy and sugars from the leaves down into the underground tubers. This "curing" process in the ground helps toughen the skin of the tubers, making them more resilient to rot and dehydration during storage.
The Waiting Period
Once the foliage has blackened, we recommend waiting about 7 to 10 days before you start digging. This short window allows the tubers to fully enter dormancy. However, you should not wait too long. If the ground begins to freeze several inches deep, the tubers themselves can be damaged.
If you live in a climate where a hard frost doesn’t arrive until very late in the year, you can manually trigger dormancy in mid-November by cutting the stalks down to about six inches. This tells the plant it is time to rest, even if the weather is still mild.
Key Takeaway: Wait for the first frost to turn the leaves black, then give the tubers about a week in the ground to toughen up before you begin lifting them.
Preparing to Dig Your Tubers
Before you grab your shovel, a little preparation goes a long way in keeping your varieties organized. Once the stems are cut and the tubers are out of the ground, many varieties look identical.
Labeling and Identification
Organized gardening is happy gardening. Before you cut the stalks, ensure every plant is clearly labeled. You can use waterproof garden markers to write the variety name on a plastic tag and tie it securely to the base of the stem.
Some gardeners prefer to write directly on the skin of the tuber later in the process using a soft lead pencil or a felt-tip marker, but a stem tag is the best first step. Knowing which tuber produces a 4-foot tall Cafe au Lait and which produces a 2-foot "Gallery" variety is essential for planning your garden layout next spring.
Cutting the Stalks
Using a pair of clean, sharp loppers or hand pruners, cut the dahlia stalks down so only 4 to 6 inches of the stem remains above the soil line. These short "handles" make the clumps easier to manage as you dig.
Be aware that dahlia stems are often hollow. In some cases, they can act like a straw, funneling water down into the crown of the tuber clump. If heavy rain is in the forecast between the time you cut the stems and the time you dig, you can loosely cover the hollow tops with a bit of aluminum foil to keep the interior dry.
The Lifting Process: How to Dig Without Damage
Dahlia tubers are surprisingly fragile, especially at the "neck," which is the thin part where the tuber connects to the main stem. If the neck is broken or severely cracked, the tuber usually won't grow because the "eye" (the growth point) is located right at that junction. For a visual walkthrough, see our How to Lift and Store Dahlia Bulbs.
Choosing the Right Tool
A garden fork is generally better than a shovel for lifting dahlias. The tines of a fork can slide through the soil with less resistance and are less likely to slice through a hidden tuber. If you only have a shovel, just be extra cautious about your spacing.
Step-by-Step Digging
- Find the Perimeter: Start by placing your fork in the soil about 12 inches away from the main stem. Dahlias can grow quite wide underground, and you want to avoid stabbing the tubers.
- Loosen the Soil: Gently push the fork into the ground and rock it back and forth. Move in a circle around the plant, loosening the soil on all sides.
- Lift Gently: Once the soil is loose, slide the fork deep under the center of the clump and gently pry it upward. Use your other hand to grasp the stem "handle" and help guide the clump out of the hole.
- Shake and Inspect: Gently shake off the large clods of soil. Avoid banging the tubers against a hard surface, as this can bruise the skin or snap the necks.
Key Takeaway: Dig wide and use a garden fork to lift the clumps. Treating the tubers gently now prevents rot issues later in the winter.
Cleaning and Drying Your Dahlias
Once the tubers are out of the ground, they need to be cleaned and dried before they go into long-term storage. There are two main schools of thought on cleaning: washing with water or dry-brushing.
To Wash or Not to Wash?
Washing the tubers with a garden hose makes them much easier to inspect for damage, pests, or rot. It also makes the "eyes" easier to see if you plan on dividing them immediately. However, if you wash them, you must be extremely diligent about drying them afterward. Any moisture trapped in the crevices of the clump can lead to mold.
If your soil is sandy and falls away easily, you can simply let the clumps sit in a dry, frost-free area (like a garage) for a day and then brush off the remaining dirt with your hands or a soft brush. This "dry" method is often safer for beginners because it minimizes the risk of excess moisture.
The Initial Dry (Curing)
Regardless of how you clean them, the tubers need to "cure" for 24 to 48 hours. Place them in a cool, shaded, and well-ventilated area. A porch, shed, or garage works well. Do not leave them in direct sunlight, as this can cause the skins to shrivel too quickly.
Many gardeners find it helpful to turn the clumps upside down during this drying period. This allows any water trapped inside the hollow stems to drain out, protecting the crown from rot.
To Divide Now or Later?
One of the most debated topics among dahlia lovers is whether to divide the tuber clumps in the fall or wait until the spring. At Longfield Gardens, we believe both methods can work, and the best choice depends on your schedule and storage space.
The Case for Fall Division
Dividing in the fall is often easier because the tubers are soft and easy to cut. You also save a significant amount of storage space because you aren't storing "blind" tubers (those without eyes) or the old "mother tuber" (the original one you planted).
The challenge with fall division is that the "eyes" can be very difficult to see. The eyes are small bumps or nodes near the neck that will eventually become next year's stems. In the fall, they are often dormant and nearly invisible.
The Case for Spring Division
Waiting until spring allows the eyes to begin swelling, making them much easier to identify for a beginner. You simply take the whole clump out of storage in March or April, find the sprouts, and cut them apart then. The downside is that the tubers become quite tough over the winter, often requiring more force or a sharper knife to separate.
What Makes a Viable Tuber?
If you do choose to divide, remember that every individual piece must have three things to be successful:
- The Body: The fat part of the tuber that holds the energy.
- The Neck: The narrow part that must be intact and unbroken.
- The Crown/Eye: A piece of the main stem's base that contains at least one growth bud.
A tuber without an eye is just a potato—it will never grow a plant. For a closer look at tuber anatomy, see Dahlia Tubers: What You Need to Know. If you aren't sure where the eyes are, it is always safer to store the clump whole.
Selecting the Right Storage Medium
Dahlia tubers are like Goldilocks—they don't want to be too wet, or they will rot, and they don't want to be too dry, or they will shrivel up and die. The storage medium you choose acts as a buffer to keep moisture levels just right.
Common Storage Materials
- Peat Moss: This is a very popular choice. It holds a tiny bit of moisture but stays fluffy enough to allow air circulation. If using peat moss, ensure it is only very slightly damp, not wet.
- Vermiculite: This mineral is excellent for storage because it is sterile and does a great job of regulating humidity. It is often the preferred choice for gardeners who struggle with rot.
- Wood Shavings or Pine Bedding: Often sold for pet cages, these are inexpensive and provide good insulation. They are very dry, so you may need to check your tubers more often for shriveling.
- Perlite: Similar to vermiculite, but it doesn't hold as much moisture. It’s a good choice if your storage area is naturally humid.
The Container
You can store your prepared tubers in cardboard boxes, plastic bins with holes drilled for ventilation, or even heavy-duty paper bags. Some gardeners use plastic grocery bags loosely tied, though you must be careful not to seal them completely, as the tubers need to "breathe" slightly.
Creating the Ideal Storage Environment
Location is everything when it comes to preserving dahlia bulbs. You are looking for a spot that stays consistently cool but never reaches freezing.
The Temperature Sweet Spot
The ideal temperature for dahlia storage is between 40°F and 50°F (4°C to 10°C).
- If it gets too cold (below 35°F): The cells in the tubers will freeze and burst, turning the tuber into a black, mushy mess.
- If it gets too warm (above 55°F): The tubers may think it is spring and start to sprout prematurely, or they may simply dry out and shrivel.
Common locations include unheated basements, crawl spaces, or a corner of a garage that is insulated enough to stay above freezing. We recommend keeping a simple thermometer in your storage area so you can monitor the temperature during the coldest parts of January.
Humidity Considerations
Humidity should ideally stay around 75% to 85%. In many modern homes with central heating, the air becomes very dry in the winter. If your storage area is dry, you may need to mist your storage medium (the peat moss or shavings) once or twice during the winter to keep the tubers plump.
What to do next:
- Choose a storage spot that is dark and cool (40–50°F).
- Prepare your storage containers with a few inches of peat moss or vermiculite.
- Place tubers in the container so they aren't touching each other.
- Cover them completely with more storage medium.
Overwintering Care: The Monthly Check-up
One of the most common mistakes is "setting and forgetting" your dahlias. Even with the best preparation, things can change over the winter. We suggest checking your tubers once a month.
Checking for Rot
If you find a tuber that feels soft, slimy, or has a foul smell, remove it immediately. Rot can spread quickly from one tuber to the next. If only a small part of a large clump is rotting, you can sometimes cut away the bad part with a clean knife and let the healthy section dry out before putting it back.
Checking for Shriveling
If the tubers feel light, rubbery, or look like a wrinkled prune, they are losing too much moisture. This is an easy fix. Lightly mist the storage medium with a spray bottle of water. You don't want it to be "wet," just slightly humid. The tubers will often absorb this moisture and plump back up.
Dealing with Early Sprouts
If you see small white or green shoots starting to grow in February, don't panic. It usually means your storage area is a bit too warm. Move the box to a cooler spot if possible. You don't need to snap the sprouts off; just leave them be until planting time.
Preparing for Spring: Waking the Tubers Up
As the days get longer in March and April, it’s time to think about the upcoming season. You don't have to wait until the last frost to start working with your dahlias.
Pre-Sprouting (Optional)
Many gardeners like to "wake up" their tubers indoors about 4 to 6 weeks before the last frost date. This gives the plants a head start, leading to earlier blooms in the summer. To do this, simply take the tubers out of storage, place them in a tray of damp potting soil, and put them in a warm, bright spot. Once the eyes start to sprout, you know they are ready for the garden. For the planting step, see How to Plant Dahlias.
Hardening Off
If you have pre-sprouted your dahlias indoors, remember that they have been living in a protected environment. Before planting them in the ground, spend a week "hardening them off." This means taking them outside for a few hours a day, gradually increasing their exposure to wind and direct sun. This prevents the tender new growth from getting "sunburned" or shocked by the outdoor air.
Safety and Practical Considerations
While dahlias are beautiful, it is important to remember that they are not meant for consumption. Keep your storage boxes away from where you store potatoes or onions to avoid any confusion.
Additionally, dahlia tubers can be mildly toxic to dogs and cats if ingested in large quantities, causing digestive upset or skin irritation. When you are digging and storing your bulbs, ensure they are kept in a place where pets cannot get to them.
Finally, remember that gardening is a partnership with nature. Some years, despite your best efforts, a few tubers might not make it through the winter. Weather fluctuations, unexpected humidity changes, or the natural lifespan of a variety can all play a role. Don't let a few lost tubers discourage you—the ones that do survive will be more than enough to fill your garden with beauty.
Conclusion
Preserving dahlia bulbs is a simple and rewarding way to extend the life of your garden and enjoy your favorite flowers year after year. By following the natural cycle of the plant—waiting for the frost, lifting with care, and providing a cool, stable winter home—you ensure a spectacular display for the next growing season.
At Longfield Gardens, we believe that the time you spend protecting your tubers in the fall pays off in the incredible colors and textures of the summer garden. If you want a ready-made dinnerplate mix for next season, browse the Dahlia Dinnerplate Cloud Nine Collection. Every tuber you save is a promise of more beauty to come.
- Wait for the first frost to signal dormancy before digging.
- Label your varieties clearly to stay organized for spring.
- Store in a cool (40-50°F), dark place with a moisture-buffering medium.
- Check your tubers once a month to ensure they are neither rotting nor shriveling.
"The secret to beautiful dahlias isn't just in the planting; it's in the careful rest you provide them during the winter months."
For more help planning your next garden, you can explore our variety of gardening articles and guides or shop Spring-Planted Summer-Blooming Bulbs. We look forward to seeing your garden grow!
FAQ
Can I leave my dahlia tubers in the ground if I mulch them heavily?
If you live in USDA zones 8 or warmer, you can often leave dahlias in the ground with a thick layer of mulch to protect them from light frosts. However, in zones 7 and colder, the ground freezes deep enough that mulch is usually not enough to prevent the tubers from rotting or freezing. For a broader overview of dahlia care, see All About Dahlias.
My tubers feel a bit soft but aren't rotting; are they still good?
A slightly soft or "rubbery" tuber is often just a bit dehydrated. As long as there is no mold, slime, or foul smell, they are usually still viable. You can lightly mist your storage medium to help them rehydrate, and they will typically perform just fine once planted in moist spring soil.
Do I have to wash all the dirt off before storing them?
No, you do not have to wash them. In fact, many gardeners prefer to leave a little bit of soil on the tubers as it can act as a natural protective layer. The most important thing is that the tubers are dry to the touch before they go into their winter containers.
What should I do if my tubers start growing long, white sprouts in storage?
This is usually a sign that your storage area is too warm or the tubers are getting too much light. Move them to a cooler, darker location if possible. You can leave the sprouts on the tuber; they will often turn green and start growing normally once you plant them in the spring.