How to Tell if Dahlia Tubers Are Dead?


I bet you don’t want to figure out that dahlia tubers are dead late in the growing season. How can you tell if they’re dead?
By     

Chances are, you’re here for one of two reasons. #1—You forgot to dig your dahlias up for the winter, and you’re worried you made a fatal mistake. #2—you did dig them up, but they’re not looking so great after storage. If you’re worried your dahlia tubers are dead, you’ve come to the right place.

Trying to tell if your dahlia tubers survived or if they need replacing isn’t always easy. So let’s talk about worrisome signs to look for, reasons why you may have lost them, and how to avoid dead tubers in the future.

Signs Your Tubers Are Dead

Even the most experienced gardeners will struggle to determine if tubers are dead. It is normal for them to dry out during the winter—especially if you dig them up and store them—but if there is even a tiny amount of viable, moist flesh inside, they are still alive and send up new shoots. However, the following visible signs indicate significant problems.

  • Visible mold on the tuber.
  • Soft, squishy spots (rot) give way when you press on them.

Even if you do see considerable problems with your tubers, it’s hard to know if the tuber is entirely dead or not. If the mold or rot is severe, the chances the tuber is still alive is almost nonexistent, and it’s best to cull it from your collection. 

It is often recommended that you err on the side of caution and assume your dahlia is dead, but if you think there’s a chance, even if small, give it a chance to grow and see what happens.

Can I Save Rotten Tubers?

Honestly, you may be able to save rotten tubers. Dahlias are known to be survivors, and shoots appear from tubers you’ve given up on and discarded into the compost pile. Sometimes the mold or rot hasn’t spread through the tuber, so it is still salvageable if you give it the following extra care. 

Collected rotten tubers in a table

How to Try to Save Them

If tubers are in the ground, dig them out and brush as much soil off them as possible.

1. Sterilize Your Equipment

Bacterial or fungal infection generally causes rot, so start by sterilizing all of your tools with a bleach solution at 1 part bleach to 9 parts water. Make sure to clean your pruners or scissors after every cut.

2. Cut Off Infected Areas

Carefully inspect each tuber, gauging how much it has rotted or how much mold is on the outside. Cut away the infected areas using scissors, pruners, or a pruning knife. Make small cuts, gradually cutting off more until you reach hard, unrotted flesh.

3. Treat Cut Edges

To keep the cut edges from reinfection or rot, you should treat them with a sulfur-based fungicide or sulfur dust before replanting. When working with these products, carefully follow label instructions.

4. Treat Contaminated Soil

If you think the planting bed is infected, you need to treat the contaminated soil to prevent spread. Soil drenches are one of the most effective fungicide applications, but keep in mind they also kill beneficial bacteria.

5. Replant Prepared Tubers

You can always plant the questionable tubers back into the garden, but I recommend initially putting them into a container. Using a container ensures any remaining disease can’t spread through the soil, infecting neighboring plants.

If the tuber is viable, you’ll see new growth shortly. Once you see sprouts, you can transplant it to the garden or keep it in the container for the season.

small dahlia tubers ready to be planted

Reasons Your Tubers Died

Overwatering, leaving them in the ground in cold climates, and improper storage conditions are the most prevalent causes. Tubers are the reproductive part of the dahlia plant, and these fleshy storage organs do not fare well when exposed to too much water. But insects and diseases (which are often related to wet conditions) could be the cause too.

The Best Ways to Keep Your Tubers Healthy

Watering Dahlias to Minimize Tuber Rot

Overwatering dahlias is the leading cause of tuber rot. With only a thin skin covering the tuber, they are highly susceptible to rot if the soil is too wet.

After planting tubers, there is no need to water them until they sprout and develop their first set of true leaves. Once they form, water soil deeply when it dries out. 

The Best Time to Dig Out Tubers

We’ve talked in previous articles about needing to dig tubers up in colder climates and when to dig your tubers in the fall.

The goal is to enjoy the flowers as long as possible while getting them out before they can rot. Dig them up after they’ve been planted for at least 120 days or after the first killing frost.

A person digging out a large tuber in the garden

Getting Tubers Ready for Storage

After your tubers are out of the ground, proper preparation helps minimize problems during storage. You want the tubers clean and dry before you pack them away for the winter. This preparation cuts down on the incidence of rot or mold significantly. It’s a prime situation showing how prevention is much easier than treating problems. 

  1. First, cut the plant’s stems off about 2 inches above the swollen, fleshy tuber.
  2. Wash excess soil off the tubers and roots. If you use your garden hose, keep the spray gentle, so you don’t damage or break them.
  3. Divide any large clumps into smaller pieces for next spring’s planting.
  4. Lastly, set the cleaned tubers in the sun to dry for a couple of days.

Properly Storing Tubers for The Winter

After your tubers are dry, it’s critical to store them properly in a cool (40-50°F), dark place until spring. These conditions keep them dormant, so they don’t start growing while preventing rot or mold growth. Depending on the numbers, you can throw them in a paper bag with sawdust or pack them layered in a bin.

gloriosa rhizomes in sawdust

Packing them in a bin is best to keep them protected in storage. Not only does separating them minimize damage to the tubers from jostling, but it also minimizes the spread of pathogens that may be present.

  1. Start by choosing a container large enough to hold your tubers. A plastic storage container or Styrofoam ice chest works well.
  2. Layer two inches of peat moss, sand, or perlite in the bottom of the container.
  3. Set the individual tubers on the bottom layer, leaving at least two inches of space between them.
  4. Cover this layer with another two inches of peat moss, sand, or perlite.
  5. Repeat as necessary.
  6. Always finish with a layer of material.

Optimal Winter Storage Conditions

As mentioned above, the ideal storage temperature is between 40 and 50°F. You don’t want the container to freeze because freezing will burst cells inside the tuber (like what would happen if left outdoors during winter). You also want the storage area to be dark or dimly lit. Ideal locations include basements or garages.

Carley Miller
Carley Miller is a horticultural expert at Bustling Nest. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.
More ArticlesFlowers and Ornamentals