Worm castings – your soil’s superfood

When, how and why to use worm castings


Worm castings are an incredibly diverse and beneficial soil additive. Used in addition to a fertilizer, worm castings are versatile and have abundant benefits. Though you may take precautions for use on acid-loving plants, they can be used freely on everything else.


  • Mix around 10-20% or less castings into your soil mix for plantings
  • Add some castings to the bottom of your hole before planting
  • Monthly:
    • Add a few teaspoons to house plants (read about acid-loving plants below)
    • Top dress with a ½ to 1 inch thick layer, 2-3 inches around the stem of plants and water it in
    • Side dress by adding castings to the surface and gently tilling them into the soil
  • Combine worm castings with water to form a “tea” and water directly


  • Worm castings have a neutral to slightly alkaline PH, around 6.5-7.5 depending on the conditions under which the worm castings were farmed
  • This may unbalance the soil conditions for particular plants that love acidic soil
  • A soil acidifier along with PH testing may be used to restore the PH


  • Contains phosphorous, nitrogen, zinc, iron, potassium, magnesium, copper and calcium
  • Will improve soil’s capacity to hold and exchange nutrients
  • Worm castings hold moisture
  • An enzyme in worm called chitenase repels aphids, spider mites, scale insects and others. The chitenase not only acts in the soil, it is taken up into the plant where it can also repel insects such as white flies.
  • New beneficial worms may hatch from worm eggs potentially present in the castings
  • Castings are excellent for use as a compost starter
  • Beneficial microorganisms such as beneficial soil bacteria, beneficial microscopic worms called nematodes and also protozoa that eat harmful soil bacteria are found in worm castings.