Composting Dahlia Tubers with Worms: The "Popsicle" Method

Like many dahlia growers, I end up with large quantities of non-diseased but non-viable tubers. This happens first after planting time and again after end-of-season dividing.

While dahlia leaves and stems compost easily, dahlia tubers stubbornly resist decay and often sprout in the warmth of my worm-rich compost bins. This creates a common dahlia waste problem for gardeners who want efficient composting.

Vermicompost , or worm compost, is a nutrient-rich soil amendment created when earthworms break down organic matter. It improves plant growth by increasing the availability of nutrients, especially nitrogen, phosphorus, and potassium, in forms plants can easily absorb.

Vermicompost also boosts soil's microbial activity, promoting beneficial bacteria and fungi that aid in nutrient cycling and disease resistance. Its fine texture improves soil structure, increasing water retention and aeration.

Additionally, it contains plant growth hormones (like auxins and cytokinins) and humic substances that stimulate root development and overall plant vigor. Repeated studies show that plants grown with vermicompost often have increased yields, improved resistance to pests and pathogens, and a greater tolerance to environmental stress.

As Rhonda Sherman, author of The Worm Farmer’s Handbook and a world-renowned expert in vermicomposting, points out, "Vermicast is just packed with microbes." These microbes, along with high levels of humic and fulvic acids, are the "real star of the show" in vermicompost, contributing significantly more to plant growth than just its NPK ratio.

For a deeper dive into the science behind these powerful soil amendments, listen to her insights on the Joe Gardener podcast.

Before I started gardening, I thought worms just "eat" vegetable matter. But worms like Eisenia fetida (red wigglers) do not have the enzymes to break down fresh plant material directly. Instead, they rely on microbes, bacteria, and fungi that colonize decomposing organic matter.

Here's how it works:

• Microbes colonize leaves, food scraps, and other organic waste as it begins to rot.
  
  

• This microbial action softens and partially breaks down the materials.
  
  

• Worms then consume a mixture of the decaying matter and the rich microbial community growing on it.

So, worms are technically eating microbially pre-digested organic matter, along with the microbes themselves, which are a significant source of protein and nutrients for the worms. This microbe-worm synergy gives vermicompost its extraordinary biological richness. You get a highly active blend of worm-cast microbial ecosystems and plant-ready nutrients.

Understanding your worms is key to successful vermicomposting. As Rhonda Sherman emphasizes, it's crucial to recognize that you are practicing "earthworm husbandry," caring for animals that need specific conditions to thrive.

The Eisenia fetida species, commonly known as red wigglers, are ideal for vermicomposting because they are "epigeic" earthworms. This means they naturally live above ground in decomposing organic materials like leaf piles or manure, not in soil. This is why you should never fill a worm bin with dirt, and also why adding these composting worms directly to your garden beds is usually a mistake, as they will not survive conditions like full sun or dry soil.

So how can I use the biomass that hundreds of dahlias produce every season, while recycling those nutrients through the magic of worms? The tubers take forever to rot, and the worms cannot work their magic until they do.

After pondering that question, I came up with the idea of intentionally freezing my non-viable (and otherwise unwanted) dahlia tubers. This simple dahlia tuber composting trick allows the worms to break them down quickly.

Here's how to turn your dahlia tuber waste into worm food:

• Step 1: Collect Tubers. Gather your non-viable dahlia tubers after planting or end-of-season dividing.
  
  

• Step 2: Freeze Solid. Fill a kitchen garbage bag with the tubers and put it in a chest freezer for a couple of days until they are solidly frozen.
  
  

• Step 3: Thaw to Mush. After they are frozen solid, empty the tubers into a garbage can next to your compost bins. Allow them to thaw, soften, and begin turning to mush. Freezing effectively breaks down the cellular structure of the tubers, making them much easier for microbes and worms to process.
  
  

• Step 4: Feed Your Worms. As you layer in “browns” like wood shavings and cardboard, together with “greens” such as grass clippings and kitchen waste, place a generous scoop of mushy tubers right in the middle.

Within days, the worms find them and go wild, gobbling up the feast and making babies to continue their good work.

We all know never to let our dahlia tubers freeze if we are trying to store them. But I thought you guys might be interested to hear how and why I have started freezing some of mine on purpose!

For more practical tips on setting up and managing a successful worm bin, including common missteps to avoid, explore the second part of Joe Gardener's conversation with Rhonda Sherman.

Want to understand why these tubers are so valuable in the first place? To learn more about the science of dahlia tuber formation and their critical role in the seasonal life cycle of these marvelous flowers, check out my 7-part series, Dahlia Tubers Demystified.