Are worms harmful to my garden?

Are worms harmful to my garden?

By Teresa J. Frith


Thousands of kinds of worms inhabit the Earth, and while many are very good for your garden, there are some that aren’t. Worms are like the intestines of our planet because they burrow all throughout the dirt, eating and processing the soil and leaving behind their castings, otherwise known as worm poop. 

They can produce their weight in castings daily, which are a mix of organic material, minerals, as well as other things plants need like nitrogen, calcium, potassium, magnesium, sulfur and iron. These worms therefore are enriching and helpful to the environment, and welcome in a garden.


Worm categories

Most worms can be placed into one of three categories:

  • Those that live in litter – These worms, for example red worms, live amongst the leaves and plant debris, and are the ones used for composting to help turn food waste into rich fertilizer. 
  • Those that live in topsoil – These worms, for instance earthworms, live within the top 2 or 3 inches of the soil. They eat soil and organic material and burrow around, aerate the soil and leave their castings behind to enrich the soil.
  • Those that live deep underground – These worms, for example nightcrawlers, live between 5 and 6 feet underground, and generate vertical tunnels where they deposit their castings. These are not excellent choices for composting but are beloved by fishermen since they are large and well taken be most types of fish.

The types described above are helpful worms and are good for gardens in most cases. They can help turn barren ground into rich, fertile dirt for growing plants. However, there are other harmful species of worms gardeners should try to avoid.


Bad worms

Nematodes are tiny worms about a millimeter long. Many are parasitic and bad for your garden, though there are a few which actually prey on the bad types. Several other bad species include roundworms, heartworms, tapeworms, and hookworms. These can live in the dirt, and not only do they harm gardens, if their eggs are ingested by humans or other animals, they can cause drastic problems or even death.

A few examples of other bad worms you may see infesting a garden include inchworms and cankerworms, which are actually larvae of moths, as well as cutworms, and wireworms, which are all destructive to both food crops and flowers. 


In a few cases, worms like red worms or earthworms could be harmful, even though usually they are welcome in the garden. If they move into an area where the species of plant life requires a layer of leaves and other organic debris for their seeds to germinate and grow, and these worms eat all of it up or chew on their roots, then those plants will die.


One way to protect your garden is to learn how to tell the difference between good and bad worms. For instance, if  you can see the segmentation lines on a worm, it is a good species, while if the worm’s body is smooth and lineless, these are the bad worms you don’t want in your garden.

All in all, many kinds of worms are welcome inhabitants of your garden since they aerate the soil, leave their rich castings to be used as fertilizer, and help break up dirt so plant roots have a better chance of growing in a fertile environment. They work like a plow moving the dirt and mixing in the organic material on top into the dirt, thus enriching bad dirt into good dirt for growing plants.

So, the key to having a thriving garden is to learn to identify the worms seen in your garden, then take measures to eradicate the bad ones, and welcome the good ones. If you'd like a controlled environment, you can consider purchasing a worm bin.