What are worm castings and how do I use them?

The (not-so) secret power of worm castings

Compost Cab members have the unique opportunity to get finished compost and worm castings delivered to their door as part of our innovative soil give-back program. Our lucky members are happy to use the local, organic compost as a soil amendment in their garden beds. Members also have the option to receive worm castings as part of our program. But there’s one question we get all the time:

What are worm castings?

Worm castings are top of the line in the world of composting. They are essentially earthworm manure; a mix of soil, sand, and digested organics. Cool, huh? The castings resemble football-shaped particles the color of rich, black soil. In fact, most people have a hard time telling soil and worm castings apart. The mixture of worm castings and finished compost is a powerful organic fertilizer known as vermicompost.


  • Worm castings improve soil aeration and drainage, as well as increase water retention in the soil.
  • Added to potted plants, worm castings help prevent plant diseases by absorbing toxins and bad fungi and bacteria.
  • Worm castings help prevent extreme pH levels in the soil from stopping plant growth. The castings act a barrier around the roots, keeping plants strong!
  • Worm castings aggregate in such a way that they help retain water. The mineral clusters that form keep the soil from eroding.

How do I use worm castings?

The beauty of worm castings is that you can’t overfeed your plants with it. It simply won’t burn plants like other types of fertilizer. It really is a foolproof method.

  • A general rule of thumb to follow is to use 3 pounds of worm castings per 100 square feet of garden space.
  • For indoor plants, feed each plant with about 1/2 cup of worm castings every 2 months during the growing season. Simply place on top of the soil and water over the castings.
  • Outside in the garden, place 1 to 4 inches of worm castings on the surface level of the soil and work it in.
  • Worm Casting Tea: You can make Worm Castings into a tea for your garden by soaking a few tablespoons of Worm Castings in a gallon of water overnight. The tea can then be strained or used directly to water house and garden plants, it can even be sprayed onto plant leaves.
October 24, 2016

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