Air & Water
What You Didn’t Know to Put In—and Keep Out—of Your Compost

What You Didn’t Know to Put In—and Keep Out—of Your Compost

January 21, 2023

By Megan Boyle, Editorial Director

Compost requires three essential components: 1) brown matter, which provides carbon; 2) green matter, which provides nitrogen; and 3) water, since moisture is needed to help everything break down.

Most of us know the basics: dead leaves for brown, grass clippings and vegetable scraps for green, plus some dew, rain, or even a splash from the hose. (Green matter typically includes at least some moisture of its own.)

But what about dinner last night? Or odds-and-ends in your yard? Here’s a list of some lesser-known ingredients to add to your compost and those to keep out.

Put In!

  • Egg shells, nut shells (omit leaves and twigs of the black walnut tree, which contain the toxin juglone)
  • Saw dust and wood chips (but not if treated with any chemicals)
  • Coffee grounds and tea bags (don’t forget to remove staples)
  • Hair and fur
  • Fireplace ashes

Keep Out!

  • Pet waste (may contain parasites or harmful bacteria)
  • Meat, bones and dairy products (may generate odor and attract pests)
  • Coal, charcoal ash (may be harmful to plants)
  • Diseased plants (may transfer the disease to your compost and infect future plants)
  • Yard clippings treated with chemical pesticides

Remember: the quality of your compost depends on the materials you put in it. By including matter containing or treated with potentially toxic chemicals, you may be adding the residue of these harmful substances to your soil as well.