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Question: I have a garden box on legs, so no contact with the ground. Should I add earthworms to it?
Anne St. Jean
Answer: No, it’s not a good idea for several reasons.
First, to avoid the worms suffering needlessly. The environment inside a pot is not ideal for earthworms. Here are some possible problems:
• The soil temperature can change too quickly and drastically, notably becoming too hot for worms.
• Occasionally, the soil can to dry out completely, which can kill them.
• Sometimes after a good watering or a heavy rain, the soil becomes thoroughly soaked with water and the worms can drown.
• There is not always a large enough mass of potting soil in a container to support worms.
• Worms live in association with beneficial microbes that may be lacking in this functional, but artificial environment.
In case of a planter raised off the ground, earthworms become prisoners of an environment that can easily become hostile to them. Often, moreover, they die fairly quickly there.
The same is true of container gardens set on an inert surface (concrete, asphalt, deck, etc.) and of plants grown in fabric pots without drainage holes (they don’t need drainage holes, as excess water will drain through the tissue that makes up the pot). These also become earthworm prisons.
Now, had the planter been in contact with the soil and with drainage holes large enough for worms to move through, the situation would be different. At least that way the worms could migrate out of the container into the soil below when the conditions don’t suit them … and return to the container when they do. Even so, if you try this, 10 to 1 the worms will leave the planter and never return, which is, I feel, quite revealing. Not that they don’t sometimes move into a pot and stay, but that’s fairly unusual. Mostly, they prefer living in the ground underneath.
Earthworms sometimes end up indoors in houseplant pots. More on that in the article Earthworms in Your Houseplants?
Plus, There Are No Real Benefits
In addition, although worms are widely considered useful in in-ground gardens where they aerate soil with their tunnels and enrich the soil with their waste, these effects are less advantageous in pots.
First, we don’t usually use soil taken from the garden—often a dense and compact soil that would benefit from a bit of earthworm plowing—in pots, but rather a growing mix based on peat, coir and perlite. Thus, it’s a soil that is naturally well aerated and doesn’t need the help of earthworms. And we enrich it with regular applications of compost and fertilizer. As a result, earthworms raised in containers don’t really give you any special benefits.
If you want to enjoy the benefits of earthworms without making them suffer, why not add vermicompost (earthworm compost) to your soil, whether you make it yourself or buy it commercially? That way, nobody suffers and everybody wins !