Introduction
There is nothing quite like the peak of dahlia season. These spectacular flowers bring a sense of abundance to the garden with their incredible colors and diverse shapes. As the cooler air of autumn arrives, you might feel a bit of nostalgia for those summer blooms. However, at Longfield Gardens, we see the end of the season as a rewarding transition. Harvesting your dahlia tubers—often called bulbs—is an exciting way to preserve your favorite varieties and even grow your collection for next year.
This guide is designed for home gardeners who want to ensure their dahlias survive the winter to bloom again. We will walk you through the timing of the harvest, the best way to lift the tubers without damaging them, and how to prepare them for a cozy winter rest. By following a few simple steps, you can turn a single season of beauty into a lifelong gardening hobby.
Taking care of your dahlias now sets the stage for a spectacular show next summer. Let’s look at how to harvest your dahlia bulbs with confidence and ease.
When to Harvest Dahlia Bulbs
Timing is perhaps the most important part of a successful dahlia harvest. While it might be tempting to dig them up as soon as the weather cools, waiting for the right environmental cues ensures the tubers are mature and ready for storage.
Watching the Weather
Dahlias are native to the warm climates of Mexico and Central America. They are not built to survive freezing ground temperatures. In most parts of the United States, the signal to begin the harvest is the first "killing frost." This occurs when temperatures drop low enough to turn the lush green foliage of the dahlia plant black or dark brown.
You do not need to panic the moment you see frost on the grass. A light frost might only nipped the top leaves, but a killing frost will clearly end the plant's growth for the season. This event is actually a helpful milestone. It tells the plant to stop putting energy into flowers and start tucking it away into the tubers underground.
The Importance of the "Wait Period"
Once the foliage has blackened, we recommend waiting about 5 to 10 days before you start digging. This brief waiting period is highly beneficial for several reasons:
- Eye Development: This time allows the "eyes" (the small buds that will become next year’s stems) to become more visible. This makes it much easier if you plan to divide your tubers later.
- Skin Toughening: The outer skin of the tuber begins to toughen up or "cure" while still in the ground. Thicker skin helps prevent the tubers from drying out or shriveling during the winter.
- Energy Transfer: The plant sends its remaining nutrients down into the root system, ensuring the tubers are plump and healthy.
If you live in a region where a hard frost doesn't occur until very late in the year, you should aim to harvest your tubers by mid-November. The goal is to get them out of the ground before the soil itself freezes solid, which can damage the water-filled tubers.
Preparing Your Dahlias for Digging
Before you reach for your shovel, a little preparation goes a long way. Proper organization in the fall prevents confusion in the spring.
Labeling for Success
Once the stems are cut and the tubers are out of the ground, many dahlia varieties look remarkably similar. It is nearly impossible to tell a Cafe Au Lait dinnerplate dahlia from a 'Thomas Edison' decorative dahlia just by looking at the roots.
The same is true for a Thomas Edison decorative dahlia.
To keep your garden organized, label your plants before you cut them back. You can use waterproof garden markers to write the variety name directly on the lower part of the stem, or attach a weather-resistant tag. At Longfield Gardens, we find that labeling at this stage is the best way to ensure your color schemes remain perfect for the following year.
Cutting Back the Foliage
After you have waited your 5 to 10 days post-frost, it is time to remove the spent foliage. Use a clean, sharp pair of loppers or hand pruners to cut the main stalk.
Leave a "handle" of about 4 to 6 inches of stem sticking up out of the ground. This stem serves two purposes: it marks the exact location of the tuber clump so you don’t accidentally strike it with a shovel, and it gives you something to hold onto as you gently lift the clump from the soil.
Key Takeaway: Always label your dahlias before cutting them back. Use the "handle" method by leaving 6 inches of stem to make digging safer and easier.
Step-by-Step: How to Dig Your Dahlias
Dahlia tubers are surprisingly fragile. The "neck" of the tuber—the narrow part where it connects to the main stem—is easily broken. If a tuber breaks off and loses its connection to the crown (the area with the eyes), it will not be able to grow next year.
Choosing the Right Tools
A sturdy garden fork is often better than a traditional shovel for harvesting dahlia tubers. The tines of a fork can slide through the soil and loosen it without the "slicing" action of a shovel blade. This reduces the risk of cutting a tuber in half. If you only have a shovel, simply be extra cautious with your spacing.
The Digging Process
- Establish a Safety Zone: Start your digging about 10 to 12 inches away from the main stem handle. This ensures you are outside the main "clump" of tubers.
- Loosen the Soil: Insert your fork deep into the ground and gently pry upward. Work your way in a full circle around the plant. This "circles the wagons" and ensures the roots are loose on all sides.
- The Gentle Lift: Once the soil is loose, slide your fork under the center of the clump. Place one hand on the stem handle and use the fork to lever the clump upward.
- Avoid Pulling: Never try to yank the dahlia out of the ground by the stem like a carrot. The weight of the soil clinging to the tubers can snap those fragile necks instantly. Lift from below while supporting from above.
Cleaning and Inspecting the Tubers
Once the clump is out of the ground, you will likely have a large ball of soil surrounding the tubers. Cleaning them properly is essential for preventing rot during the winter.
To Wash or Not to Wash?
There are two main schools of thought on cleaning dahlias, and the right choice usually depends on your soil type.
- The Wash Method: If you have heavy clay soil, the dirt can stick like glue. Using a garden hose with a gentle spray nozzle is the easiest way to remove this soil. Wash the tubers thoroughly until you can see the crown and the individual roots.
- The Brush Method: If you have loose, sandy soil, you may not need water at all. Let the clump sit in a dry, shaded area for an hour or two. The soil will often dry and fall away with a light brush of your hand or a soft brush.
Regardless of the method, the goal is to remove as much organic matter as possible. Soil contains bacteria and fungi that can cause the tubers to decay if they stay damp during storage.
Identifying Health and Rot
While cleaning, take a close look at your harvest. A healthy tuber should feel firm, similar to a fresh potato. If you notice any tubers that are mushy, shriveled, or have a foul odor, remove them immediately. These are signs of rot, and keeping them with the healthy tubers can cause the decay to spread.
Check the "mother" tuber as well. This is the original tuber you planted in the spring. It is often darker, more wrinkled, and larger than the new tubers the plant produced over the summer. While some gardeners keep the mother tuber, many choose to discard it, as it is more prone to rot and may not produce as vigorously the second year.
Pro Tip: If you see any signs of insect damage or small holes, don't worry too much. As long as the tuber is firm and the crown is intact, it should store just fine.
Dividing Your Dahlia Tubers
Dividing is the process of cutting the large clump into individual tubers. This is how you multiply your collection! You can divide in the fall or wait until the spring.
Finding the Eyes
The "eye" of a dahlia is a small, slightly raised bump on the crown. This is the only part of the tuber that can produce a new sprout. If a tuber is cut off without a piece of the crown and an eye, it will not be able to grow next year.
If you find it difficult to see the eyes in the autumn, don't feel pressured to divide now. Many gardeners wait until spring when the eyes naturally begin to swell and turn pink, making them much easier to identify.
Sterilizing Your Tools
If you do choose to divide your tubers in the fall, cleanliness is paramount. Use a sharp, thin-bladed knife or heavy-duty floral snips.
Between each plant, dip your tools into a solution of 10% bleach and 90% water, or wipe them down with rubbing alcohol. This prevents the spread of viruses or diseases from one plant to another. In our trial gardens, we have found that tool hygiene is one of the "quiet winners" of successful dahlia care.
What to do next:
- Shake off large clumps of soil immediately after digging.
- Rinse tubers gently to avoid puncturing the skin.
- Trim away thin, hair-like feeder roots with clean snips.
- Inspect for "firmness" and discard any soft spots.
- Allow the tubers to air dry in a frost-free area for 24 hours.
Curing and Drying for Long-Term Storage
Once your tubers are clean and (optionally) divided, they need to "cure." Curing is a fancy word for letting the exterior dry out slightly so the tuber creates a protective seal.
Place your tubers in a cool, dry area with plenty of air circulation. A garage, basement, or covered porch works well, provided the temperatures stay above freezing. Avoid placing them in direct sunlight, which can cause them to dry out too quickly and shrivel.
Curing usually takes about 1 to 3 days. You want the surface to feel dry to the touch and any cut ends (from dividing or trimming) to look calloused over. If the weather is very humid, you might need an extra day. Just be careful not to leave them out for weeks, as dahlias can lose too much moisture and become "mummified."
For more step-by-step storage help, read How to Overwinter Dahlias.
Winter Storage Methods
The goal of storage is to keep the tubers in a state of suspended animation. You want them cool enough that they don't sprout, but warm enough that they don't freeze. You also want them dry enough that they don't rot, but humid enough that they don't shrivel.
Temperature and Humidity
The "sweet spot" for dahlia storage is between 40°F and 50°F. A dark, unheated basement, a crawl space, or a cool corner of a garage (that doesn't drop below freezing) is ideal.
Humidity should ideally be around 80%. If your storage area is very dry, you may need to check on your tubers once a month and give them a very light misting of water. If the area is damp, ensure you have good air circulation to prevent mold.
Storage Mediums
Rarely do we store tubers completely "naked" in a box. Using a packing medium helps regulate moisture and protects the tubers from temperature swings. Popular choices include:
- Vermiculite: This is a mineral that holds onto moisture and is very clean. It is one of the most popular choices for preventing shriveling.
- Peat Moss: A classic choice that is slightly acidic, which can help inhibit some fungal growth. Ensure it is slightly damp, but not wet.
- Pine Shavings: Often sold as pet bedding, these provide great air circulation and are very affordable.
- Newspaper: Some gardeners simply wrap each tuber in several layers of newspaper and tuck them into a cardboard box.
At Longfield Gardens, we recommend using a container that can "breathe." Cardboard boxes, milk crates, or plastic bins with the lids left slightly ajar are all excellent options. Avoid airtight plastic bags, as they trap moisture and almost always lead to rot.
Realistic Expectations for Your Harvest
Gardening is a partnership with nature, and results can vary based on your local climate and soil conditions. It is perfectly normal to lose a few tubers over the winter. Even the most experienced growers expect a small percentage of loss.
If you check your tubers in January and find one has gone soft, simply toss it out and check its neighbors. This "checking in" is part of the fun of gardening in the off-season. It keeps you connected to your plants and ensures that the majority of your collection stays healthy and ready for spring.
Also, keep in mind that dahlia tubers are toxic if eaten by pets or humans. When harvesting and storing, keep them in a place where curious dogs or cats cannot reach them.
For more growing guidance, see 8 Tips for Growing Better Dahlias.
Conclusion
Harvesting dahlia bulbs is a satisfying way to wrap up the gardening year. It transforms a seasonal flower into a long-term investment that brings more beauty to your yard every summer. By waiting for the frost, digging with care, and storing your tubers in a cool, dark place, you are giving your plants the best possible start for the next season.
We love the way dahlias can make any garden feel like a professional flower farm. Whether you are saving a single favorite variety or a whole rainbow of colors, the effort you put in now will be rewarded with a burst of blooms next July.
Key Takeaways for Success:
- Wait for a killing frost and then give the tubers a week to cure in the ground.
- Use a garden fork to lift the clumps gently from the outside in.
- Clean and inspect every tuber, removing any that feel soft or mushy.
- Store in a cool (40-50°F), dark place using a medium like vermiculite or pine shavings.
If you are looking to expand your collection or want to try new flower forms, we invite you to explore the Summer Lovin collection at Longfield Gardens. Planning next year’s garden starts today!
"The simple act of saving dahlia tubers connects the beauty of last summer to the promise of the next, making every bloom feel like an old friend returning to the garden."
For a bold, color-coordinated mix, the Berry Spritz collection is another easy way to add more blooms next season.
Or try the High Summer Mix for warm-toned flowers that keep the display going.
FAQ
Do I have to dig up my dahlias every year?
This depends on your USDA hardiness zone. If you live in zone 8 or warmer, your ground likely does not freeze deep enough to kill the tubers, so you can often leave them in the ground with a thick layer of mulch. However, in zones 7 and colder, the ground will freeze, and dahlias must be harvested and stored indoors. If you are not sure of your zone, check the Hardiness Zone Map.
What if I accidentally cut a tuber while digging?
Accidents happen! If you slice a tuber in half, it is best to discard that specific piece, as the open "wound" is very susceptible to rot. However, as long as the rest of the clump and the main crown are undamaged, the plant will still be perfectly healthy and viable for next year.
Can I store my tubers in the refrigerator?
While the temperature of a refrigerator (usually around 35-38°F) is close to the ideal range, it is often a bit too cold and too dry for dahlias. Additionally, some fruits and vegetables release ethylene gas, which can damage the tubers. A cool basement or garage is generally a much safer and more effective choice.
Why did my tubers shrivel up during the winter?
Shriveling is caused by a lack of humidity in the storage area. If the tubers look like raisins, they have lost too much water. You can try to revive them by soaking them in room-temperature water for 24 hours before planting in the spring. To prevent this, ensure your storage medium is slightly damp or check them more frequently to provide a light misting of water.
