How Beneficial is Worm Compost


How beneficial is it in a garden. In my area, someone is selling a 10 lb. bag for $10. How much does one use – I have a large garden.

Tge seller calls it worm compost but I thought it was called worm casings/castings. Is it the same thing?


These are all great questions.

Up until a few years ago we would have said without hesitation that organically produced earthworm castings, also called earthworm compost, are a great choice of soil amendment if you want to add a naturally produced fertilizer, humus, beneficial bacteria and fungi to your soil. They increase the organic content of the soil and its ability to hold moisture.

Although worm castings are not a complete fertilizer, the nutrients they release benefit plant growth and are easily taken up by plants. They have been shown to improve seedling growth rates and are a cost effective way to convert vegetable waste into fertilizer if you have your own vermicompost bin (worm bin)

The quality of the castings is dependent on the quality and type of food given to the worms and how the worms were cared for. Lower quality castings may contain weed seeds, high soluble salt content and have an acidic pH, which can be a problem for some plants.

With the recent invasion of  ‘Jumping Worms’  from the US into Ontario, Canada, we have become aware of the potential risk of buying just ANY bag of worm castings. Compost has been found to be one of the vectors that can carry Jumping Worm eggs. It is now important to ask questions about the provenance, or place of origin, of the worm castings for sale and how they were produced. Questions like – Have they been produced in a vermicompost bin or very close to the ground? Have the worms been fed compost that has been in contact with a compost pile outside? Have the worms for the composter been purchased from a reputable supplier? Has the worm species been identified by the seller?

Jumping worms are greedy eaters and outcompete other earthworms. Their castings degrade soil quality, which can cause the loss of soil nutrients- significantly compromising the health of our native plant species and creating soils more susceptible to erosion.

In 2021 Jumping Worms were found in Toronto soils. Since they can migrate into vermicomposters that are on the ground, and lay their tiny eggs, it is important to make sure your bags of castings have been produced with care. Ideally, the vermicomposter should have legs that elevate the bin above ground level, all gardening gloves and tools used to maintain the vermicomposter should be clean, only fresh vegetable/fruit waste should be used to feed the worms- not leaves or food scraps from an outdoor compost pile (which could be contaminated with Jumping Worm eggs). If your worm castings seller is an avid vermiculturalist, they wont mind you asking.

For an established garden, apply about 1-2 cups of worm castings per established plant – or a quarter of a cup per 6 inches diameter of plant size. Apply as a top dressing to the soil around the root zone- or from the drip line to the trunk.  It is reported that UV light can kill the good microbes in the vermicompost, so if your plant root zone is in a sunny spot, gently scratch the castings into the surface of the soil for maximum effect. Repeat 1-2 times per year.

For planting a new container or garden plant add approximately 10% worm castings to the planting soil to promote healthy root development.  It is recommended that you continue to add organic compost and mulch to your garden to supplement your castings.

Hope you find this information helpful.