E-mail -- Worm Castings and Soil Amendments

Hello Doc,

I’m doing a soil mixture of : soil, perlite, peat moss, and worm castings. How much of each in a two gallon pot. Specifically the worm castings, a few cups each, or a few ounces each? please help.

Hi
The good news is that you can not really use too much worm castings. Many places recommend up to 10-30% of your medium consist of worm castings. You could start by adding 2 cups of castings per 1 gallon and see how the plants do with that.  (There are 16 cups in a gallon so 2 cups per gallon would be 12.5% worm castings)  I would also recommend using coir instead of peat moss, as coir is a renewable resource and peat moss is basically mined from wetlands.  Either one can make your medium more acidic so you need to keep an eye on that.  Adding some lime to your mixture (1 table spoon per gallon of medium) will help keep the pH in a good range.
Ultimately, how much of any medium amendment you use will depend on the type of plant you grow, plants that need lots of fertilizer you can use three or more cups of worm casting per gallon, plants that do not need nutrients as much you can give less.
You could also do a little experiment and give some plants more worm castings and see if you can notice a difference. That way you will know what *you* need for *your* plants.
Good growing,
Dr. E.R. Myers