Darwin was writing about the humble but mighty earthworm.



Earthworm castings (a fancy word for worm poop) can best be described as Mother Nature’s super-food; they energize your plants and provide a suit of armor against harmful pests.

Used for centuries by growers, worm castings have long been recognized as a most helpful and beneficial tool. They improve the soil, and they also do much more.

While many gardeners do their own earthworm composting, many don’t have the time or space to do so. Fortunately, ready-to-use worm castings may be purchased from garden centers and nurseries and applied directly to the soil.

Here are some fun facts (and some nerdy facts) about earthworm castings, thanks in part to Donald W. Trotter, PhD. Trotter’s natural gardening columns appear nationally in environmental publications.

What Are Earthworm Castings? What’s In Them?

  • “Worm casts are digested organic matter that has been run through the gut of the earthworm. They are one of the most stable sources of organic matter for the garden and the biology they support is unlike that of any regular commercial or home-made compost. Earthworms impart into their casts an incredible diversity of hygienic microorganisms that work to competitively exclude disease-causing organisms as well as a number of destructive pests such as root knot and root lesion nematodes.” (Trotter)

  • Earthworm castings contain chitinase (“KITE-ten-ace”), an enzyme that dissolves chitin. Many pest insects, such as whiteflies, are made of chitin. So when chitinase gets sucked up by plant roots and pests try to ingest the sap, their insides are dissolved and they die. Trotter writes, “There can be no more effective way to control pest insects on plants than this method because insect pests cannot change what material makes up their bodies.” Worm castings are also “loaded with other beneficial, hygienic microorganisms that will help your plants fight such regular maladies as powdery mildew, rust, black spot, and a number of other fungal pathogens.” (Trotter) This is done by the above-mentioned competitive exclusion, the process by which one species dominates and eventually prevents another from surviving.

What do worm castings do in/around the soil?

Sometimes it can be difficult to get soil to grab on to passing water. We have all watered a garden or a pot, and found soil afterward that hasn’t absorbed any of the water, which seems to just pass over it. Worm castings act as nature’s most effective wetting agent, or surfactant. Chemistry labs work to create this quality that can be naturally provided by the worms. Earthworm castings inherently provide a moist and healthy environment for plants to flourish.

This is fantastic, but Earthworm castings also do much more:

  • Unlike other forms of manure, worm castings fertilizer is ready to use immediately.

  • As mentioned above, earthworm castings fight pests on plant surfaces by dissolving them – whiteflies and many other insects are made up of the very materials that worm castings dissolve.

  • Worm castings release many beneficial nutrients slowly so that they don’t burn the roots of plants like chemical fertilizers can do.

  • Earthworm castings remove heavy metals and toxins from soil.

Worms have been known to ingest organic matter that is laced with heavy metals, thus removing the contaminants from soil and prohibiting their uptake by plants.

  • Long-chain organic molecules like diesel fuel are routinely broken down into their less problematic parts. In the same way, worms and other microbial life in the soil are effective at cleaning up soil.

  • Their high CEC (cation exchange capacity) means that the worm castings hold onto heavy metals, thus preventing these contaminants from being absorbed by the plant roots. Metals don’t accumulate in leaves to be eaten by people and other animals.

  • Earthworms fragment long-chain organic molecules, so the castings they leave behind recycle nutrients that are more digestible by plants.

  • Earthworms are major decomposers of dead and decomposing organic matter.

  • Earthworm castings absorb moisture and release it slowly which reduces water use.

  • Earthworms and their castings naturally aerate the soil, which helps get oxygen to the roots of plants. The mucus that the worms secrete as they digest their food provides a natural flocculating effect on the soil, leaving it like a barrel of popcorn balls that have space to absorb oxygen, water, and nutrients. All of this improves seed germination and plant growth.

How do I apply Earthworm Castings?

Trotter recommends, “When applying worm castings to the garden, it should be known that the best place for them is where your plants do the majority of their feeding, the dripline. Worm casts should be applied in a ring of about three-quarters to one inch in thickness around the dripline of your plants for maximum insect and disease repellency. This ring should be in the form of a band of between six inches to two feet wide depending on whether you’re using it on smaller shrubs or trees. A layer of organic compost over the top of the casts will help to keep them moist and protect them from the sun depleting their biology, which is sensitive to the rays of the sun.”

You may also create a “tea” by soaking the castings in water. One cup of castings in two gallons of water, soaked overnight, may then be poured over vegetables, flowers, hanging baskets and houseplants. Apply the remaining solids from the bottom of the container to the surface of the soil.

Are Earthworm Castings Harmful to Humans?

Earthworm castings are completely safe; they will not harm kids, pets, or wildlife.

What about House Plants? Do earthworm castings help indoors?

YES! Repotting plants in a blend of fresh potting soil and earthworm castings will revive houseplants that need a little love. Keep healthy houseplants lush and beautiful by sprinkling two tablespoons of castings over the surface of healthy houseplants and watering well.

Best of all, earthworm castings are odorless. Plant parents can pick up a cup of castings for their indoor plants, treating them to an organic bath of protection and nutrition without the odors that may be associated with other organic solutions.

Where Can I Find Worm Castings?

To find a garden center near you that carries “Nature’s Superfood” (Earthworm castings), just click on this Store Locator, visit the garden center or nursery, and ask for them by name.

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“Hey Don, What’s All This Buzz About Worm Castings?” Article by Donald W. Trotter, Ph.D. Trotter can be reached at Curly@mill.net, and you can find his books in stores or online, published by Hay House Publishing.

Science Learning Hub (https://www.sciencelearn.org.nz/resources/9-earthworms-role-in-the-ecosystem)

Additional resources: https://www.kellogggarden.com/blog/soil/the-importance-of-garden-worms/


For more detail about how to raise your own worms, check out The Worm Farmer’s Handbook: