Earthworms are probably the gardener’s best friend. They help turn the soil to keep it fluffy and rich in nutrients.
But are they also good for your potted houseplants? Do earthworms eat plant roots?
Even though their main and preferred diet is decaying plant matter, earthworms feed on living plant roots and even seeds when there is limited availability of their preferred food. It is thus not suitable to put worms in pots, especially if the pot is smaller than 16 inches (40 cm) in diameter.
In this article, we will show you what earthworms eat, the best worm species to put in your container garden, and when it is not a good idea to put them in your potted houseplants.
1. Do earthworms eat live roots?
Earthworms feed on living roots as they feed on the bacteria in the root zone.
A study shows that earthworms feed on the young roots of legume seedlings and grass seedlings (Emmanuel et al., 2010). It is believed that they eat the root hairs incidentally as they feed on the soil microbes that are concentrated in the rhizosphere or the root zone.
Observing their feeding behavior also confirms that earthworms do feed on fine root hairs (Gunn & Cherrett, 1993).
Several studies also found small quantities of plant root substances in the guts and castings of earthworms (Cortez & Bouche, 1992; El Harti et al., 2001, Baylis et al., 1986).
Apart from plant roots, they also feed on plant seeds by collecting plant seeds at the soil surface and moving them to their burrows in the deeper soil layers (Regnier et al. 2008). Some seeds fail to germinate because they are moved too deep down into the soil. Those seeds that survived germinated faster and grew into bigger seedlings (Eisenhauer et al., 2010). The castings and mucus of the earthworms are believed to have helped in breaking seed dormancy and accelerating germination.
Seeds and seedlings are believed to be quality food to supplement their diet of dead, decomposed organic matter.
It must be noted that the studies were performed in pots, where the availability of space and preferred food could be a factor for them to feed on living plant roots. Although they consume living plant roots, living plant roots are not their preferred, main diet.
The diet of earthworms mainly consists of dead, decaying plant tissues (e.g. dead roots, rotting seeds, leaves, animal manure, and dead animals). They also eat living and dead microbes, fungi in the soil, and even some soil particles to facilitate digestion.
Earthworms that feed on the decaying plant litter and animal manure near or at the soil surface are called “detritivores”. There are two types of detritivores: “epigeic” earthworms that both feed and live at or near the soil surface, and “anecic” ones that feed on the surface but live in burrows deep in the mineral soil.
They are in fact quite selective in their food choices and prefer dead, decaying organic matter. They consume leaves only when they are decomposed by the microbes after a period of time, instead of freshly fallen leaves (Satchell, 1967).
They also prefer finer materials than coarse ones, and protein- and carbohydrate-rich litter than that with lower protein content.
3. Should you put worms in potted plants?
Whether it is a good idea to keep earthworms in potted plants depends on many factors.
In general, it is not suitable to keep worms in potted plants due to the following factors:
Pot size too small
The pot size is probably the most important factor because it determines how much space the worm can move around to seek out the best food and environment with best moisture and other living conditions.
Worms are definitely not suitable for pots or containers smaller than 16 inches (40 cm) or 10 gallons (38 liters). Most houseplants are in pots much smaller than this. It is hard to maintain a rather constant level of moisture in a small pot. The soil either is too dry or too moist after watering and the worm would have nowhere to move to and would eventually die or escape.
Also, if there is not enough space and thus little food available, they would most likely be eating plant roots as mentioned previously in this article.
Sterilized potting mix
If your plant is potted in a commercial potting mix, it is often sterilized with no living microorganisms and organic content and thus there will not be food for worms. Starving worms could feed on the living plant roots or escape out of the pot.
Growing medium becomes too loose
Most houseplants fit in the pot snuggly with only a little space left for the soil. Having worms in the pot would loosen the soil too much and the root ball would lose its body.
If it is in a pot or garden that is big enough, the worms would have enough space to move around and will not necessarily be limited near the root area.
Chunky growing medium breaks down quickly
For plants that require more aeration around the roots, your chunky growing medium such as bark chips may break down more quickly than expected because of the existence of earthworms. This would reduce the particle size of the growing medium, which would become too waterlogged for the plants.
Use worm castings instead
The major benefit of having worms in the soil is mainly for aerating the soil and their worm castings. You can put worm castings in your potted plants as a fertilizer for your plants and to increase the drainage and water retention of your soil.
This video shows the results of an experiment of putting worms in small pots:
Not all worms are beneficial for the garden and plants. The best are two types of earthworms, namely the nightcrawler worms (better) and red wigglers.
Nightcrawlers (Lumbricus terrestris), or simply “garden worms”, are most commonly seen in garden soil.
They are brown in color. They are “anecic” earthworms as they make vertical burrows in the soil to travel to feed on the topsoil, collect their food and drag it to their burrows in the subsoil.
They are light-sensitive (hence their name) and wait until it is dark to burrow to the top of the soil to feed on the decaying plant litter. They turn and aerate the soil as they plow through different layers of soil back and forth the top layer and a lower layer of soil.
There are two types of nightcrawlers.
- Canadian nightcrawlers can grow between 11 – 14 inches (28 – 36 cm) long and are highly sensitive to warm temperatures.
- European nightcrawlers can grow between 2.5 – 3.5 inches (6 – 9cm) long.
Red wigglers (Eisenia fetida) are considered “composting worms” and are usually used in vermicomposting.
They are reddish-brown in color and usually grow up to 2 to 3 inches (5-8 cm) long, which is shorter and also thinner than the nightcrawlers.
The red wigglers are most recognized for their function in producing worm castings as fertilizer as they digest food more quickly than nightcrawlers.
These worms can eat plenty of food and kitchen scraps such as moldy bread, grains, nail and hair clippings, feces, rotten fruits and vegetables, and shredded newspapers.
If you put red wigglers into your potted plants, be careful with the number because they reproduce faster than nightcrawlers.
5. How to keep earthworms in containers?
If you have a pot, container, or grow bag that is bigger than 16 inches (40cm), you may consider the following aspects in keeping earthworms together with your plants.
- Put only a few worms in each pot. Overpopulation may lead to other issues such as competition for food which may eventually affect your plant.
- Put some dead leaves, compost, or even kitchen scraps in the growing substrate.
- Avoid using excess organic fertilizer as it may burn the worms
- Avoid overwatering
- Make holes in the pot so that extra water may flow out to prevent the soil from becoming too soggy.
Putting earthworms in pots would likely affect the plant because they feed on living plant roots if there is not enough food available.
Worms would also be affected living in small pots because it is difficult to keep an optimal moisture content throughout. They suffer from either too much or too little moisture and have no space to go to find their preferred environment.
It is thus not suitable to introduce worms into pots or containers that are smaller than 16 inches (40 cm) or 10 gallons (38 liters).
Baylis, J.P., Cherrett, J.M. & Ford, J.B. (1986). A survey of the invertebrates feeding on living clover roots (Trifolium repens L.) using 32P as a radiotracer. Pedobiologia 29, 201–208
Cortez, J. & Bouche, M. B. (1992). Do Earthworms Eat Living Roots?
Curry, J. P. & Schmidt, O. (2007). The feeding ecology of earthworms – A review. Pedobiologia, Vol 50 (6), Pp. 463-477
Eisenhauer, N., Butenschoen, O., Radsick, S., Scheu, S. (2010). Earthworms as seedling predators: Importance of seeds and seedlings for earthworm nutrition. Soil Biology and Biochemistry, 42(8): 1245-1252
Gunn, A. & Cherrett, J.M. (1993). The exploitation of food resources by soil meso- and macro-invertebrates. Pedobiologia 37, 303–320.
Regnier, E., Harrison, S.K., Liu, J., Schmoll, J.T., Edwards, C.A., Arancon, N., Holloman, C. (2008). Impact of an exotic earthworm on seed dispersal of an indigenous US weed. Journal of Applied Ecology 45, 1621-1629.
Lavelle, P. (1988). Earthworm activities and the soil system. Biology and fertility of soils, 6(3), 237-251.
Marquis, R. J., Lill, J. T., & Piccinni, A. (2002). Effect of plant architecture on colonization and damage by leaftying caterpillars of Quercus alba. Oikos, 99(3), 531-537.
Masters, N., & Soils, I. The benefits of worms and vermicast.