What Not to Compost

As easy as composting with nitrogen-rich "greens" and carbon-rich "browns" can be, there are some things you don't want in your compost. Most ingredients you can collect locally are perfectly safe, but knowing some minor details will help prevent a batch of contaminated material from ruining your garden.

Popular "greens" include grass clippings, coffee grounds, herbivorous animal manure, kitchen scraps, freshly pulled weeds and other plant debris.

Scraps or grounds from just about anything a person would eat or drink can be composted without worry. However, don't try to compost meat, dairy products or very oily foods (like shortening). They won't break down in the regular gardener's compost.

If you collect grass clippings from your own or a neighbor's yard, be sure no weed killers, pesticides, weed-n-feed type fertilizers or other herbicides were used on the lawn in the past year. Clippings from lawns treated with a basic N-P-K or even iron-based moss control fertilizers are fine, even if they're not organic. (But don't use moss control lawn fertilizers directly on your garden.)

If you want to compost animal manure, be sure to only use manure from animals that eat plants, like cows, chickens, horses and rabbits. Be sure the animals weren't treated with hormones or antibiotics, which can really disrupt the life cycle of soil organisms. Don't use manure from meat-eating animals like cats, dogs or humans. Feces from carnivorous animals can contain dangerous bacteria, parasites, and even viruses.

If you make a hot compost pile that heats up to 140-160 degrees F, you can compost most weed seeds. But if you make cold compost, avoid weeds that have gone to seed. You should also avoid any plants infected with blight, fungal wilt, club root, viruses or other diseases. Throw those plants away in your regular household trash.

If you live near a lake, you may have thought about composting that pesky, feathery water weed milfoil (Myriophyllum sp.). However, studies show that milfoil is good at sucking up toxic heavy metals; something you don't want in your garden.

Easy to find "browns" include fall leaves, sawdust, paper or straw bales. If you compost sawdust, be sure it didn't come from pressure treated wood, a manufactured wood product (like oriented strand board, particle board, etc.), or from wood that had finishes like paint, deck stain or lacquer applied.

You may have heard rumors that hickory leaves are bad for compost, or that oak leaves make compost too acid, but don't believe them. You can even use a shovel-full or two of wood ashes (but not barbeque or coal ashes) in your compost.

Most newspaper, office paper, cardboard, and junk mail can be composted, but don't compost glossy magazines. Remember that paper is very dry, so be sure to dampen it well when adding it to your compost.

In the fall and winter you can generally find bales of straw that are tempting to use in compost or as winter mulch. However, Washington has historically had a problem with a persistent herbicide called clopyralid (klow-PEER-uh-lid). Many farmers use clopyralid on hay, grains and other crops to kill weeds, but it remains in the soil, passes through grazing animals, and survives even the hot composting process. It will then frizzle your broadleaf plants. If you are offered bales of hay or straw, be sure to ask if there's any chance clopyralid was used before you accept them.

Copyright © 2005 Brian Ballard. All rights reserved.