Skip to main content

What to Do About Moldy Dahlia Tubers

Some dahlia tubers I was storing are moldy. Can I treat them somehow and plant them?

dahlia osaka

Answer: Dahlias are wonderful additions to the garden, bringing in bursts of radiant, vivid hues. Unfortunately, once dahlia tubers become moldy, there isn’t much that you can do but discard the ones that are damaged and only plant those that are not.

Although it is too late for your dahlia tubers that have become moldy, here are some tips on proper storage, to prevent having to throw any away in the future:

Dry: The first step, after digging and dividing of course, is to make sure that your tubers are dry before storing. How long it takes to dry them depends mostly on your climate conditions, but it's at least 3 to 4 days. The skin will begin to toughen when dried, but make sure you do not overdry the tubers—you will know if they are getting too dehydrated if they begin to shrivel up.
Container: There are many different ways to store dahlia tubers, just choose the method that works the best for you. You can place the tubers in a cardboard box (or a plastic container, wooden box, etc) and line the box with newspaper or plastic wrap. Add peat moss to the base of the container and place the tubers on top of the peat moss (vermiculite, wood chips or sand also work well). Add an additional layer of peat moss on top of the tubers, and then you can repeat this step—applying the tubers, then peat moss again—until the box is full. Gently close the container, but do not seal it completely, and store it in a dark, cool place. You can also put the tubers in a plastic bag—one designed to hold produce so it contains breathing holes, or a mesh bag, with or without the peat moss inside, and then place inside of the container. This can help with separating different varieties without having to use multiple boxes.
 Temperature: Once you have figured out how you want to store your dahlia tubers, you need to pick the perfect location. Ideal temperatures should be 40 – 50 Fahrenheit, with medium humidity—typically in a basement or garage.
Check tubers: You want to check on the dahlia tubers at least once a month to make sure the temperature is not too warm or too cold and that the tubers are not drying up. If they look a little shriveled, squirt with a water bottle. Remember to remove any tubers that appear to be rotting or acquiring mold.

It is important to choose the storing conditions that work best for you, whether using peat moss or vermiculite, bag or no bag, or if you choose a cardboard box or plastic container. With the right temperature, a dark room and monthly water squirts and check ups, your tubers will have a better chance of being healthy enough to plant next season.

Image: Dahlia 'Osaka' by Cillas
Peruse through creative techniques and essential tasks for growing stunning flowers with the Smart Gardening Techniques: Flower Gardening.

Take the stress out of summer gardening and ensure your success by downloading the Smart Gardening Techniques: Summer Tasks.

Want to plant bulbs and tubers? Check out the Smart Gardening Techniques: Gardening with Bulbs & Tubers for some insightful tips.

Explore over 100 gardening recommendations in Decoding Gardening Advice.

Need gloves with dexterity and gripping control, even in hot and/or wet conditions? Check out the Stretch Collection with Leather Palms by Womanswork.