Last week I posted a list of twenty types of things you could compost. This week we’ll look at the other side of the coin, since there are also some things you should never compost (or put in a wormery). Here’s a list of eight of them, along with the reason why they’re not good composting materials:
1) Black walnut tree leaves or twigs. This tree releases substances that might be harmful to plants, and composting it might spread these substances where you don’t want them.
2) Coal or charcoal ash. This includes ashes from your outdoor grille. Companies add all kinds of chemicals to encourage quick ignition and consistent burning, and you wouldn’t want these transferred to your compost pile.
3) Dairy products (e.g., butter, egg yolks, milk, sour cream, yogurt). These things spoil too quickly, can create odor problems, and could attract pests such as rodents and flies;
4) Diseased or insect-ridden plants. Diseases and insects can be amazingly hardy and could transfer to other plants when you spread your compost.
5) Fats, grease, lard, or oils. As with dairy products, these can create odor problems and could attract rodents and flies;
6) Meat or fish bones and scraps. Same problem as dairy products and fats. The basic issue with all of these is that they spoil much faster than the composting process, causing foul odors and posing a tempting target for vermin.
7) Pet wastes (e.g., dog or cat feces, soiled cat litter). These might contain parasites, bacteria, germs, pathogens, and viruses harmful to humans–all of which could pass to your vegetables or other plants.
8) Yard trimmings treated with chemical pesticides. If we want to go green we should minimize chemical pesticides in our garden, but to the extent we use them we should avoid adding anything to our compost pile that has been treated with these pesticides. The composting process depends on essential bacteria, worms, and other organisms that are all vulnerable to the chemicals.