Question

I found some small earthworms in the soil of one of my houseplants. I think they’re affecting the growth of the plant: it seems to be declining. What should I do to get rid of them?

Paul T.

Answer

Earthworms are not very common in houseplants, largely because the conditions in our homes aren’t much to their liking. Certainly, they can’t reproduce there and, moreover, remain small. Plus, there is often only one or two in the pot, not dozens.

Inevitably, you’ll find earthworms only in plants that spent the previous summer outdoors. The worms moved into the potting soil while the plant was outside and remained prisoners when it was brought back indoors in the fall.

Most home gardeners don’t even notice their plants have worms unless they repot and find worms burrowed in the soil, but sometimes you discover their castings (little heaps of poo) under the pot, near the drainage holes, or see the worms themselves when they rise to the surface after a particularly abundant watering. 

You’ll likely only find earthworms in the soil of plants that prefer moist conditions; worms just don’t thrive in soil that dries out completely between waterings.

Normally, earthworms aren’t harmful to plants. On the contrary, they’re beneficial, aerating the soil through their tunnels and enriching it with their castings. But in pots, their main food, the organic matter normally present in soil, isn’t very abundant, especially since most potting soils are largely composed of peat or coir (coco fiber), two materials slow to decompose and mineral-poor offering almost nothing that an earthworm can consume. Under those circumstances, the worms begin to eat the young roots of the plant growing in the pot and that can, of course, hinder its growth, even possibly kill it.

What to Do?

Let’s start with prevention.

Before bringing your houseplants back indoors in the fall, plunge their pots into a bucket of soapy water and keep them entirely emerged for about 20 minutes or so. Earthworms dislike both water and soap and will rise to the surface, trying to escape. You can then pick them up and put them back in the garden. This will also rid the potting mix of most other soil pests.

If you skipped the first step (soaking the plant before bringing it in), you can also eliminate any worms by letting the potting soil completely dry before watering again. That’s why you rarely find earthworms in pots of succulents and other plants that are allowed to dry out deeply on a regular basis.

If you find them in houseplants that won’t tolerate their soil drying out completely, just repeat the same treatment you should have used in the fall before bringing the plant in: give the entire rootball a 20-minute soak in soapy water, then remove any worms that show up.

In winter, however, you won’t always be able save the worms you find. After all, you can’t successfully release them outdoors if the ground is frozen. Instead, try putting them in your compost bin: it may be just warm enough to keep them alive. Otherwise… well, let’s just say that dead earthworms are an excellent composting material!