Introduction
There is nothing quite like the satisfaction of a garden filled with dahlias in late summer. From the massive, creamy petals of 'Cafe au Lait' to the bold, geometric shapes of Cornel, these plants are the undisputed stars of the autumn landscape. As the season winds down and the nights grow crisp, many gardeners face a choice: let the tubers go or save them to plant again next year.
At Longfield Gardens, we believe that saving your favorite dahlia tubers is one of the most rewarding parts of the gardening cycle. It allows you to build a larger dahlia collection over time and ensures your favorite varieties return year after year. While the idea of digging and storing roots might seem like a complex task, it is actually a straightforward process that any gardener can master with a few simple steps.
This guide will walk you through exactly when to harvest your tubers, the best way to lift them from the soil without damage, and how to store them so they stay healthy until spring. By following these practical steps, you can protect your investment and look forward to an even more beautiful display next season.
Understanding the Dahlia Lifecycle
Дahlias grow from tuberous roots, which act as underground storage tanks for energy. Throughout the summer, the plant uses this energy to produce lush foliage and those spectacular blooms we love.
As the days grow shorter in September and October, the plant receives a biological signal to start storing energy for the next year. This is when the tubers really begin to bulk up and mature. If you dig them up too early, the tubers may be thin and lack the energy reserves needed to survive a long winter in storage. Patience is your best ally during this phase of the season.
When to Dig Up Dahlia Tubers
The timing of your dahlia harvest is the most important factor for success. While you might be tempted to clean up the garden as soon as the first few yellow leaves appear, the plants usually need a bit more time to finish their work.
The Frost Signal
For most gardeners in the United States, the first fall frost is the ultimate signal. Dahlias are tropical plants at heart, and their tender foliage cannot withstand freezing temperatures. After a light frost, the leaves and stems will turn black or dark brown almost overnight.
While the sight of a blackened dahlia might look disappointing, this is actually a beneficial moment for the tubers. The "killing frost" tells the plant that the growing season is over. Once the top growth dies back, the energy is fully concentrated in the roots.
The Two-Week Rule
One of the most effective strategies we recommend is the "two-week wait." Once the frost has killed the foliage, cut the stems down to about 4 to 6 inches above the ground, but leave the tubers in the soil for another 10 to 14 days.
During this time, the dahlia tuber undergoes a process called "curing." The outer skin of the tuber begins to toughen up, and the "eyes"—the small bumps that will become next year's sprouts—become more visible. This thickened skin acts as a protective barrier, helping the tubers resist rot and dehydration once they are moved into storage.
Digging Without a Frost
If you live in a region where hard frosts are rare or arrive very late in the year, you can still dig your dahlias. Watch the calendar rather than the thermometer. By mid-to-late November, most dahlias have completed their growth cycle. You can manually trigger the curing process by cutting the plants back to 6 inches and waiting two weeks before digging, just as you would after a frost.
Key Takeaway: The best time to dig dahlias is usually two weeks after the first killing frost. This wait period allows the tubers to develop a thicker "winter skin" that improves their chances of survival in storage.
Preparing the Plants for Harvest
A successful harvest starts with organization. Before the foliage turns black and becomes unrecognizable, make sure your plants are labeled. It is very easy to tell a Thomas Edison from other dahlias when they are in bloom.
Once they are just a pile of brown roots, even a Kelvin Floodlight looks remarkably similar.
Use waterproof tags or weather-resistant markers to label the base of each plant. Some gardeners prefer to write the variety name directly on the tuber with a felt-tip marker later, but having a tag in the ground during the digging process prevents any mix-ups.
What to Do Next
- Check your local weather forecast for the first expected frost.
- Confirm all your dahlia varieties are clearly labeled.
- Gather your tools: a garden fork, a pair of loppers, and your storage containers.
- Cut the stems down to 6 inches after the frost and wait 10 to 14 days.
How to Dig Up Dahlia Tubers Step-by-Step
When the curing period is over, it is time to bring the tubers indoors. Dahlia tubers are surprisingly fragile, especially the "neck" where the tuber connects to the main stem. If the neck is broken or severely cracked, the tuber will likely fail to sprout next year.
Step 1: Loosen the Soil
Avoid using a traditional pointed shovel if possible. A garden fork (also called a pitchfork) is the preferred tool because it is less likely to slice through the tubers hidden underground.
Start by stepping back. Do not thrust the fork directly into the base of the stem. Instead, imagine a circle about 12 inches wide around the main stalk. Push your fork into the soil at the edge of this circle. Gently pry upward to loosen the earth. Work your way around the entire plant, loosening the soil on all sides.
Step 2: Lift the Clump
Once the soil is loose, slide the fork deep under the center of the clump. Use one hand to steady the "handle" (the 6-inch stem you left behind) and the other to lift the fork. The goal is to lift the entire root mass as one piece.
Avoid yanking on the stem. If the clump feels stuck, stop and loosen the soil a bit more. Heavy clay soil can be particularly stubborn and may require extra patience to ensure the tubers come out intact.
Step 3: Remove Excess Dirt
Once the clump is out of the ground, gently shake it to remove large chunks of soil. You can also use a small stick or your gloved fingers to poke away dirt from the center of the mass. Be careful not to skin the tubers, as any open wounds are entry points for bacteria.
Cleaning and Curing Tubers
There is some debate among gardeners about whether to wash tubers or leave them dirty. Both methods can work, and the choice often depends on your soil type and storage space.
Washing Pros and Cons
If you have heavy clay soil, washing the tubers with a gentle stream of water from a garden hose can make it much easier to see what you are doing. Clean tubers are easier to inspect for rot and much easier to divide. However, if you wash them, you must ensure they are 100% dry before they go into storage. Any trapped moisture can lead to mold.
If you have sandy, loose soil, you can often just brush the dirt off once it dries. Many gardeners find that leaving a little bit of dry soil on the tubers acts as a natural insulator during the winter.
Final Drying
Regardless of whether you wash them, the clumps need to dry in a protected area for 24 to 48 hours before being packed away. A garage, basement, or covered porch is ideal. Place them upside down (stems pointing toward the floor) to allow any moisture trapped in the hollow stems to drain out. Do not leave them in direct sunlight or in a spot that might freeze.
To Divide or Not to Divide?
One of the most common questions we hear is whether you should divide the dahlia clumps into individual tubers in the fall or wait until spring.
Dividing in the Fall
The benefit of dividing in the fall is that the tubers are softer and easier to cut. It also takes up much less storage space. When you divide, each individual tuber must have a piece of the "crown" (the area where the tuber meets the stem) and at least one visible "eye." If a tuber breaks off without a piece of the crown, it will not grow.
Dividing in the Spring
Many home gardeners find it easier to store the entire clump whole and divide it in the spring. In the spring, the "eyes" begin to swell and turn pink or white, making them much easier to identify. This "wait and see" approach prevents you from accidentally throwing away viable tubers or keeping ones that don't have eyes.
Key Takeaway: If you are a beginner, we suggest storing the clumps whole. It is safer for the plant and reduces the risk of cutting off the vital growth points.
Essential Winter Storage Conditions
Proper storage is the final hurdle in the dahlia lifecycle. The goal is to keep the tubers in a state of suspended animation—cool enough to stay dormant but warm enough to stay alive.
The Ideal Temperature
The "sweet spot" for dahlia storage is between 40°F and 45°F.
- Too Warm: If the temperature stays above 50°F, the tubers may begin to sprout prematurely or shrivel up due to moisture loss.
- Too Cold: If the temperature drops below 32°F, the water inside the tubers will freeze, turning them into a mushy, black mess that cannot be saved.
Unheated basements, crawl spaces, or insulated garages are usually the best locations. Avoid storing them in a standard refrigerator if possible, as the air is often too dry and may contain ethylene gas from ripening fruit, which can damage the tubers.
Managing Humidity
Dahlia tubers are about 80% water. If the air in your storage area is too dry, they will shrivel like raisins. If it is too humid, they will rot. We recommend using a storage medium to help regulate this moisture. Popular choices include:
- Coarse Vermiculite: Excellent for holding just the right amount of moisture.
- Peat Moss: A classic choice that is easy to find.
- Pine or Cedar Shavings: Often sold as animal bedding, these provide good airflow.
Choosing Your Container
Cardboard boxes, plastic bins with loose-fitting lids, or even heavy paper bags can work. If using plastic bins, do not snap the lid shut tight; leave it cracked to allow for some air exchange.
Line the bottom of your container with a few inches of your storage medium, nestle the tubers or clumps inside so they aren't crowded, and cover them completely. This creates a stable microclimate that protects them from temperature swings.
Monitoring Your Tubers Through Winter
Storage is not a "set it and forget it" task. We recommend checking your tubers once a month during the winter. This simple habit can save your entire collection.
When you check them, look for two things:
- Signs of Rot: If you see a tuber that has turned soft, slimy, or smells bad, remove it immediately. Rot can spread quickly from one tuber to another.
- Signs of Shriveling: If the tubers look wrinkled or feel light and hollow, they are too dry. Use a spray bottle to lightly mist the storage medium with water. You don't want it to be soaking wet—just slightly damp to the touch.
If you notice a small amount of surface mold, don't panic. You can usually wipe it off with a cloth dipped in a very weak bleach solution (1 part bleach to 10 parts water) and move the tubers to a slightly drier spot in your storage area.
Troubleshooting Common Issues
Even with the best care, gardening involves a bit of trial and error. Here are a few common scenarios and how to handle them:
"My tubers look like they have holes in them." This is often caused by insects like wireworms or slugs that were in the soil. As long as the holes are dry and the tuber is still firm, they are usually fine to store. If the area around the hole is soft, trim that section away before storing.
"The stems are hollow and have water inside." This is normal for dahlias. This is why we recommend curing them upside down for a day or two. If water stays trapped in the stem, it can travel down to the crown and cause "crown rot," which is fatal to the plant.
"I broke the neck of my favorite variety." It happens to everyone! If the tuber is still attached by a thin piece of skin, you can try to wrap it with a little bit of garden tape to keep it stable, but it may not survive. This is why we always recommend growing a few "backups" of your absolute favorites.
Conclusion
Digging and storing dahlia tubers is a rewarding skill that connects you to the natural rhythm of the seasons. While it requires a bit of effort in the autumn, the payoff is a spectacular garden that grows more impressive every year. By waiting for the frost, lifting the roots with care, and providing a cool, stable winter home, you are setting the stage for a successful spring and protecting your investment with our 100% guarantee.
At Longfield Gardens, our goal is to make these tasks feel achievable and fun. Whether you are saving a single Cafe au Lait or a whole field of colorful blooms, the process is the same. Gardening is a journey of learning, and each season brings new opportunities to refine your technique and enjoy the beauty of the plants you've nurtured.
Next Step: Once your tubers are tucked away for the winter, mark your calendar for early March. That’s the perfect time to pull them out, check for those first signs of green growth, and start dreaming about your next summer garden. When you're ready to add more, shop our dahlia collection.
FAQ
Do I have to wait for a frost to dig my dahlias?
While a frost is a helpful signal that the plant has finished its season, it is not strictly required. If your weather is getting very cold and wet but no frost has arrived, you can cut the plants back manually and wait two weeks before digging. The most important thing is that the tubers have had at least 120 days in the ground to mature.
Can I leave my dahlias in the ground all winter?
This depends entirely on your USDA hardiness zone. In zones 8 through 11, dahlias can often stay in the ground if the soil has excellent drainage and you apply a thick layer of mulch. However, in zones 7 and colder, the ground will freeze deep enough to kill the tubers, so digging them up is necessary for their survival.
If you are ordering replacements or new tubers, our Shipping Information page explains how we time shipments by zone.
What is the best material to store dahlia tubers in?
Most gardeners have the best success with coarse vermiculite or slightly damp peat moss. These materials help maintain a consistent humidity level around the tuber. You can also use wood shavings or even wrap individual tubers in plastic wrap, though the plastic wrap method requires the tubers to be completely dry and cured first to avoid rot.
How do I know if my dahlia tubers are still good in the spring?
Healthy tubers should feel firm to the touch, similar to a fresh potato. If they are slightly wrinkled but still firm, they are usually fine. However, if a tuber is mushy, collapses when squeezed, or is completely dried out and brittle like a twig, it is no longer viable and should be discarded.
