Aquaponic Worms FAQ

Anyone who has taught courses or given presentations about media-based aquaponics has experienced the unique reaction people have when they are told that worms are an important part of the ecology of an aquaponic system.

The expression that spreads over their faces reveals a mental connection being made between the futuristic coolness of aquaponics and the comforting familiarity of traditional, soil-based gardening.

For many, this linkage is the final piece they needed to become convinced that aquaponics truly is a natural system.

But often you will see that expression followed by a frown of skepticism. How can a creature that normally lives in terra firma possibly survive and thrive in the watery environment of an aquaponic grow bed?

We get a lot of questions like this about worms and their use in aquaponics, so I thought it was a good idea to dedicate an article to the most frequently asked questions about aquaponic worms.

Here goes…

How do worms benefit my media-based aquaponic system?

They break down the solid waste from the fish, and excess roots and other materials that plants slough off, and make them more bio-available to the plants through their excrement—vermicompost.

This additional metabolic layer in media-based systems is what allows media growers to avoid both the requirement to filter out solid waste and the requirement to frequently clean out their grow beds.

A 12-in. deep grow bed with a healthy population of worms will probably only need to be cleaned out every few years.

Vermicompost, and the tea that results from soaking vermicompost in highly oxygenated water (such as the conditions found in an aquaponic grow bed), have been studied extensively by the Soil Ecology Lab at Ohio State University and found to aid in the following pest and disease issues:

• Suppresses plant diseases, including pythium, rhizoctonia, plectosporium and verticillium
• Suppresses parasitic nematodes
• Suppresses insects and pests such as tomato hornworms, mealy bugs, spider mites and aphids

How do worms survive in an aquaponic grow bed? Don’t they drown?

We have all seen worms crawling out onto the sidewalk after a soaking rain, seemingly gasping for air. That they choose exposure to the sun and hungry birds over the water-logged soil seems to tell us that worms don’t like soaking wet environments.

And what is an aquaponic grow bed if not a soaking wet environment? The difference with aquaponics is that they do not remain constantly full of water, but rather flood, and then drain.

This allows for a drying-out period between soakings that also encourages air circulation within the grow media.

This brings me to the most important reason why worms thrive within aquaponics—oxygen.

The reason why those worms crawl from the soil to their death on the sidewalk is not because of the water, but because the water has forced the oxygen out of the soil.

In aquaponics, not only does the flood and drain action pull oxygen into the grow bed media, but the water that is circulating throughout the system is highly oxygenated.

In fact, I’ve found worms thriving within my sump tanks.

Can you ever have too many worms in an aquaponic system?

Sadly, no. My fish certainly wish there were too many worms! But the fact is that worms naturally adjust their population to match the conditions within their environment and as soon as those conditions no longer support additional worms they slow down or stop reproducing.

I’m considering a system inside my home. Will they escape?

Again, the answer is no. Worms hate the light and are happiest in the moist darkness of your grow beds.

The only time you will see your worms once they are in your grow bed is when you pull out a plant. They will be intertwined in the roots taking care of sloughed-off dead root material.

I heard that worms can carry E. coli. Is this true?

No. Only if it is present in whatever media they are living in. In fact, worms have been shown to mitigate pathogens that affect humans.

An April 15, 2010 article in the Journal of Environmental Protection titled Earthworms: Charles Darwin’s Unheralded Soldiers of Mankind stated: “The earthworms also release coelomic fluids that have anti-bacterial properties and destroy all pathogens in the waste biomass [13]. They produce ‘antibiotics’ which kill the pathogenic organisms in the waste and soil where they inhabit and render it virtually sterile. It was reported that the removal of pathogens, fecal coliforms (E. coli), Salmonella spp., enteric viruses and helminth ova from sewage and sludge appear to be much more rapid when they are processed by E. fetida. Of all E. coli and Salmonella are greatly reduced [14].”

How do I introduce the worms into my grow beds?

You should exercise common sense with the introduction of anything into your aquaponic system, whether that be a pest control spray (even if it is organic), new fish (quarantine first!) or a new source of water or media.

Accidentally introducing manure from warm-blooded animals that might harbor disease (E. coli.) into your aquaponic system would not be smart.

However, I have been told by our worm vendor that most responsible vermiculturalists rinse their worms after removing them from their compost home, at least twice, and then they use peat moss to ship them.

He said that it doesn’t make sense to ship worms in manure or compost because it gives off heat and high heat is the biggest risk when shipping worms.

That said, if you buy your worms from a less-than-professional source, like Craig’s List, or you harvest them from your own compost pile, you should clean the worms of anything sticking to them before introducing them to your aquaponic system.

Better yet, purge their systems (guts) by putting them in wetted down corn meal for 24 hours (or use oatmeal or wetted down Cream of Wheat). Then wash off the worms, and introduce them into the aquaponic system by laying them on top of the grow beds. They will quickly crawl into the media to escape the light.