by Rex Trulove

Created on: January 30, 2013

The number of people who know that composting is a great thing to do if they have plants, gardens or lawns seems to be growing constantly. Compost is a substance that helps most plants, both by giving them nourishment and for improving the tilth of the soil. At the same time, composting takes care of many leftovers that aren't going to be eaten or which have spoiled, without the need to throw them in the garbage can. However, some leftovers are suitable for the compost pile, while others are not.

Compost basics

Compost is the result of plant matter decomposition. Much of the decomposition is due to aerobic bacteria, the kind of bacteria that needs air in order to survive, as well as yeasts and molds. Aerobic bacteria in a compost pile normally don't stink much. It is true that animal matter usually also breaks down, however much of the decomposition for animal meat, fats, including milk fat, and oils is due to anaerobic bacteria, the kind that lives without air. Anaerobic bacteria do often produce a rancid smell, which makes the majority of animal products unsuitable for most home compost piles.

Composting leftovers

This is a major key to understanding which leftovers can be composted. The leftovers that go into the compost pile should not contain meat, fish, fat, oil or other meat byproducts. Vegetable and fruit peelings, trimmings and even husks can be composted, though these aren't leftovers. However, leftover vegetables, including cooked vegetables to which no butter, margarine or oil have been added, can be added to the compost pile. Old green salad and tomatoes can also be composted, as long as no salad dressing or mayonnaise has been added to them. Salad dressing and mayonnaise usually continue oils. Moldy jelly and jam can be added to the pile and even leftover juices, coffee or tea, without milk or creamer, can be put in the pile. Spoiled or over ripe fruit can also be added.

This also means that breads, pastries and cake should not be added because they usually contain oils or shortening, though some people do add these in small quantities. Still, there can be disagreeable odors if these are additions to the pile and they can attract vermin and insect pests.

Exceptions

According to Stu Campbell in his book, Let It Rot!, onions and garlic shouldn't be added to compost. This is because members of the onion family contain anti-bacterial substances, which can slow down the bacterial action of the pile. Interestingly, though, rinsed egg shells can be added, especially if they are crushed first. Egg shells can increase the amount of calcium in the compost heap and in the finished compost. 

With the exceptions in mind, it really isn't difficult to know what leftovers can be composted. If the leftovers contain no flesh, fat or oil, they can be put in a compost pile, for the most part. Composting is normally considered preferable to throwing the leftovers in the garbage can. The result, after everything has finished composting, is a rich substance that is simply waiting to be applied to growing plants or dug in prior to planting, to increase plant health. 

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