Introduction
There is nothing quite like the feeling of watching a dahlia garden reach its peak in late summer. The vibrant dinnerplate blooms and intricate pompon dahlias are a highlight of the season, and it is natural to want to preserve those specific varieties for next year. Saving your tubers is a rewarding way to expand your garden and ensure your favorite colors return every summer.
At Longfield Gardens, we want to help you make the most of your garden investment. Successfully overwintering dahlias is one of the most satisfying skills a gardener can master. While the process can seem mysterious, it really comes down to managing one simple factor: moisture. If the tubers get too wet, they rot; if they get too dry, they shrivel and lose their viability.
This guide will walk you through the practical steps to keep your dahlia tubers plump and healthy until spring. We will cover the best packing materials, ideal storage temperatures, and how to monitor your tubers throughout the winter months. By following a few straightforward steps, you can ensure your tubers stay hydrated and ready to grow when the warm weather returns. If you like planning ahead, our dahlia collections make it easy to compare forms and colors.
Understanding the "Goldilocks" Balance of Moisture
The primary challenge of storing dahlia tubers is maintaining the perfect moisture level. Tubers are essentially storage organs that hold water and nutrients for the plant’s future growth. Once they are removed from the ground, they begin to lose water through evaporation. If they lose too much, the cells collapse, and the tuber becomes a "mummy"—dry, brittle, and unable to sprout.
Conversely, if the environment is too damp or the tubers are packed while dripping wet, they become a breeding ground for fungi and bacteria. This leads to rot, which can quickly spread through an entire storage bin. The goal is to create a "Goldilocks" environment: not too wet, not too dry, but just right.
To achieve this, we focus on two things: the humidity of the storage room and the packing material surrounding the tubers. Most home storage areas, like basements or garages, have fluctuating humidity. The packing material acts as a buffer, holding just enough moisture near the tuber to prevent it from drying out while allowing the tuber to "breathe." To maintain this balance, aim for 80–90% relative humidity in your storage area. This high level of air moisture prevents the tuber from "exhaling" its internal water reserves into the surrounding space.
Timing Your Harvest for Better Storage
One of the most effective ways to prevent tubers from drying out starts before you even dig them up. The timing of your harvest plays a significant role in how well the tubers hold their moisture over the winter.
In many regions, we recommend waiting for the first frost to hit the plants before digging. A light frost kills the foliage, which signals to the plant that it is time to go dormant. This dormancy period allows the skins of the tubers to toughen up or "cure." A tuber with a thicker, tougher skin is much more resistant to drying out than one with thin, tender skin.
It is important to note that storage success can vary based on cultivar and tuber maturity. Some varieties naturally produce thinner tubers that are more prone to desiccation. Additionally, immature tubers—those that did not have a full growing season to develop—often have thinner skins and fewer energy reserves. These require even closer monitoring during the winter months to ensure they stay plump.
If you live in a climate where frost arrives very late, you can simply cut the plants back to the ground in mid-autumn. Leave the tubers in the soil for about 10 to 14 days after cutting the stalks. This waiting period accomplishes the same goal: it encourages the tubers to firm up and prepare for storage.
Key Takeaway: Patience pays off. Allowing your tubers to sit in the ground for a week or two after the foliage dies helps them develop a protective skin that locks in moisture.
Proper Cleaning and Curing
Once you have carefully lifted your tubers from the ground with a garden fork, the next step is cleaning. For a step-by-step refresher on digging and prep, see How to Prepare Dahlia Bulbs for Winter Storage: 5 Easy Steps.
There are two schools of thought here: washing them clean with a hose or simply brushing off the loose soil.
If you choose to wash your tubers, it is vital to let them dry completely before packing them away. However, "drying" in this context refers only to the surface of the tuber. You do not want to leave them out in the sun or on a concrete floor for days. Concrete is particularly good at wicking moisture away, and a tuber left on a garage floor for too long will begin to shrivel before it even makes it into a box.
We suggest letting washed tubers sit in a cool, shaded area for 24 to 48 hours. This is just enough time for the surface moisture to evaporate and for any small nicks or cuts from the digging process to "callus" over. A callused cut acts as a seal, preventing further moisture loss and protecting the tuber from rot.
If your soil is sandy and falls away easily, you might skip the washing entirely. A little bit of leftover soil can actually help keep the tubers from drying out, acting as a natural protective layer. Just be sure the soil is not soaking wet when you put them into storage.
To Divide or Not to Divide?
One of the first decisions you'll make is whether to store your dahlia clumps whole or divide them into individual tubers in the fall. If your primary goal is to keep dahlia tubers from drying out, storing the whole clump is often the safer bet. The large mass of the clump helps protect the individual tubers and retains moisture much more effectively than a single tuber on its own.
However, if you have a large collection and limited storage space, you may prefer to divide them in the fall. If you choose this route, be extra diligent with your packing medium. Individual tubers have more surface area exposed to the air, making them more vulnerable to shriveling. If you are a beginner or have had trouble with tubers drying out in the past, we recommend storing the clumps whole and waiting until spring to divide them.
Selecting the Right Packing Medium
The material you choose to wrap or surround your tubers is your best defense against desiccation (the technical term for drying out). For a closer look at what makes tubers healthy and viable, see Dahlia Tubers: What You Need to Know.
When packing, use a layering technique to ensure the best results. Start with a layer of packing medium at the bottom of your container, place a layer of tubers on top, and then cover them completely before adding another layer. Ideally, tubers should not touch each other; this spacing ensures that each tuber is fully buffered by the moisture-regulating medium and prevents any rot from spreading between neighbors.
Vermiculite: The Professional Standard
Vermiculite is a natural mineral that has been heated until it expands into light, absorbent flakes. It is widely considered the best material for keeping dahlia tubers from drying out. Vermiculite is excellent at regulating moisture; it can hold water without feeling "wet" to the touch. If your storage area is particularly dry, you can lightly mist the vermiculite before packing your tubers. This creates a humid micro-environment that keeps the tubers plump for months.
Peat Moss or Coco Coir
Peat moss and coconut coir are popular choices because they are inexpensive and easy to find. Like vermiculite, they hold moisture well. However, they can be a bit dusty to work with. If you use peat moss, make sure it is slightly damp—like a well-wrung-out sponge—rather than bone-dry. Dry peat moss can actually pull moisture out of your tubers, which is the opposite of what we want.
Wood Shavings
Pine or cedar shavings (the kind sold for animal bedding) are another good option. They provide excellent airflow, which helps prevent rot. While they do not hold moisture quite as well as vermiculite, they are a great choice if you are storing your tubers in a plastic bin that will trap some natural humidity.
The Plastic Wrap Method
Some gardeners have great success with the "Saran Wrap" or plastic wrap method. In this approach, each individual tuber is cleaned, dried, and then tightly wrapped in plastic film. This creates a completely sealed environment for each tuber, preventing any moisture from escaping. While this method is time-consuming, it is very effective at preventing drying. It also has the added benefit of isolating any rot; if one tuber goes bad, the plastic prevents the rot from spreading to its neighbors.
What to do next:
- Choose a packing material based on your storage area (vermiculite for dry spots, shavings for damp spots).
- Ensure the material is slightly "damp-dry"—not soaking, but not dusty.
- Label your tubers or the containers clearly so you know which variety is which.
Choosing the Ideal Storage Container
The container you use works in tandem with your packing material to manage moisture levels. Your choice should depend on where you plan to keep the tubers.
Plastic Bins and Totes
Plastic bins with lids are the most common choice for modern gardeners. They are excellent at trapping moisture, which is exactly what you need if you are worried about tubers drying out. If you use plastic, it is important to check the tubers more frequently for signs of condensation. If you see water droplets forming on the inside of the lid, the environment is too wet. You can simply crack the lid open for a day or two to let some moisture escape, or drill a few small vent holes in the sides of the bin.
Cardboard Boxes
Cardboard is breathable, which is great for preventing rot but risky for drying out. If you store your tubers in cardboard boxes, you will need to be much more diligent about checking them. We recommend lining the box with a few layers of newspaper or a plastic liner (left slightly open at the top) to help hold in some of the moisture provided by your packing medium.
Paper Bags
Paper bags are a middle-ground option. They are often used by gardeners who store their tubers in a root cellar or a cool, humid crawlspace. The paper allows for some gas exchange while offering a bit more protection than leaving the tubers exposed. If you use paper bags, consider nesting them inside a larger crate to provide an extra buffer against the dry air.
Finding the Best Storage Environment
The temperature of your storage area is just as important as the humidity. Temperature directly affects how fast water evaporates from the tuber. The ideal temperature for dahlia storage is between 40°F and 50°F (4°C to 10°C).
To ensure success, we recommend using a hygrometer to monitor both temperature and the 80–90% relative humidity target. For those seeking a highly controlled environment, some home growers use a temperature and humidity controller, such as an Inkbird, to manage fans or small heaters in their storage space.
Choosing the Right Setup for Your Space
Every home is different. Use this simple framework to match your storage method to your specific environment:
- Dry Basements: Basements with home heating systems are notoriously dry. Use plastic bins with lids and a moisture-holding medium like vermiculite or slightly damp peat moss. You will likely need to mist the medium more frequently.
- Damp Garages: These areas often have higher natural humidity but carry a freezing risk. Use wood shavings in cardboard boxes or open plastic bins to ensure enough airflow to prevent rot. Keep containers off concrete floors and away from exterior walls.
- Root Cellars or Crawlspaces: These are the gold standard for humidity. You can use more breathable containers like paper bags or crates with wood shavings, as the air itself will do much of the work to keep tubers from drying out.
Monitoring and Maintenance Throughout Winter
Storing dahlia tubers is not a "set it and forget it" task. To keep them from drying out, you should check on your "guests" about once a month. For another step-by-step checklist, read How to Save Dahlia Bulbs for Next Year: Easy Storage Tips.
Signs of Shriveling and Viability
Pick up a few tubers from different parts of the bin. They should feel firm, like a fresh potato. If they feel slightly soft or look wrinkled, they are starting to dry out.
- Salvageable: If the tuber is slightly wrinkled but still has some weight and "give," it is likely fine. Mist the packing material with a spray bottle to "recharge" the humidity and close the lid tightly.
- Too Far Gone: If the tuber is as light as a cracker, feels hollow, or is brittle enough to snap in half, it has become "mummified." These tubers are no longer viable and should be discarded. Similarly, if the "neck" has become thin and shriveled to the point of being thread-like, it may not be able to support a sprout in the spring.
Signs of Mold or Rot
While you are checking for dryness, keep an eye out for any fuzzy mold or soft, smelly spots. If you find a tuber that is starting to rot, remove it immediately. Use a clean, sharp knife to cut away the rotten portion if the "eye" of the tuber is still healthy, or simply discard the affected tuber if it looks beyond saving. This prevents the problem from spreading to the healthy tubers nearby.
Key Takeaway: A monthly inspection allows you to catch dryness early. A quick misting of water can "recharge" the humidity and save tubers that are beginning to wrinkle.
How to Rehydrate Dry Tubers
If you find your tubers in mid-winter and they look significantly shriveled—perhaps you forgot to check them for a couple of months—don't give up on them. Dahlias are surprisingly resilient.
You can often rehydrate tubers by placing them in a bucket of lukewarm water for a few hours (but no more than 24 hours). After the soak, let the surface of the tuber dry off so it isn't dripping, and then pack it back into fresh, slightly damp vermiculite. In many cases, the tuber will plump back up and go on to produce beautiful flowers in the spring.
It is also worth noting that a slightly wrinkled tuber is often still viable. As long as the "neck" of the tuber (the part where it connects to the crown) is intact and the tuber hasn't become completely hollow or brittle, it likely has enough energy left to sprout.
Preparing for Spring
As the days get longer and the weather warms in early spring, your tubers will naturally start to wake up. You may notice small "eyes" or pinkish bumps beginning to form on the crown of the tuber. This is an exciting sign that your storage efforts were successful!
At this stage, you can continue to keep them in their storage bins until it is time to plant. If the tubers look a little lean at this point, you can increase the moisture in the packing material slightly to help them get a head start. You can also browse our new dahlias when you are ready to plan the next season.
When it comes time to plant, we stand behind the quality of our plants at Longfield Gardens. We want you to feel confident that the tubers you have carefully stored (or the new ones you order from us) will thrive. How to Plant Dahlias can help with the next step. Remember that gardening is a journey of learning. If a few tubers dry out your first year, simply adjust your packing material or storage spot the following year. Every gardener develops a system that works best for their specific home environment.
Summary of Success
Keeping dahlia tubers from drying out is all about managing the micro-environment inside your storage containers. By following this exact storage recipe, you can ensure a high success rate:
- The Target: Aim for 40°F–50°F and 80–90% relative humidity.
- The Tools: Use a hygrometer to monitor your storage space.
- The Prep: Cure tubers for 10–14 days in the ground or 48 hours on a surface after digging.
- The Packing: Layer tubers in vermiculite or slightly damp peat moss, ensuring they do not touch.
- The Cadence: Check your tubers once a month. Mist the medium if you see wrinkles; remove any rot immediately.
What to do next:
- Wait for a frost or cut back plants in late autumn to help tubers "cure." When you're ready to shop again, start with dinnerplate dahlias.
- Use vermiculite or slightly damp peat moss to provide a moisture buffer.
- Store in a cool, dark place that stays above freezing but below 50°F. Dahlia Flower Types and Sizes is a helpful guide if you want to compare forms.
- Set a calendar reminder to check your tubers once a month and mist them if they look wrinkled. For a bigger-blooming option next season, try big-blooming dinnerplate dahlias.
The secret to vibrant summer dahlias is a little bit of winter care. By monitoring the moisture levels and keeping your tubers cool, you are ensuring a spectacular show of color for the coming season.
FAQ
How do I know if my dahlia tubers are too dry?
Healthy tubers should feel firm and solid, similar to a fresh potato or a carrot. If the skin looks wrinkled or the tuber feels flexible and "squishy" rather than firm, it is losing too much moisture. If the tuber is so dry that it feels light and brittle like a cracker, it may no longer be viable.
Can I use newspaper to keep tubers from drying out?
Newspaper is a common packing material, but it is not the most effective at preventing dryness because it breathes very easily. If you use newspaper, it is best to wrap the tubers in several layers and then place them inside a plastic bin. This way, the newspaper acts as a cushion while the bin holds in the necessary humidity.
Should I wash the dirt off my tubers before storing them?
Washing is a matter of personal preference. Some gardeners prefer washing because it makes it easier to see the "eyes" and identify any rot or pests. Others prefer leaving the soil on as it provides a natural protective layer against drying out. If you do wash them, ensure they are surface-dry before packing them in your storage medium.
Is it better to store dahlia tubers in a basement or a garage?
The best location is whichever one stays consistently between 40°F and 50°F. Basements are often more stable in temperature but can have very low humidity due to home heating systems. Garages are often more humid but run the risk of freezing. If you use a basement, you may need to mist your tubers more often; if you use a garage, keep the bins off the concrete floor and away from exterior walls.
