4 Steps to Avoid Toxic Compost

Everything from pile size to what you put in it seems to matter. Instead of giving you a recipe for composting, we decided to give you a basic understanding of the process of composting that will help you understand the deeper “why” questions. With this information, you will be composting like a master gardener in no time. 

The Four Basics

If you have read other articles about composting you may have heard about green and brown material. Unfortunately, few people understand exactly why green and brown material matter. Hopefully this article will help clear up any misunderstandings about compost.  The truth is that there are not just two, but four basic ingredients within successful compost and all of them need to be in the right balance. These ingredients are carbon, nitrogen, water and oxygen.

1. Carbon

Carbon is most commonly added to compost as brown material. Straw, hay, chipped or shredded wood, shredded paper products, or any dried plant products are high in carbon.  Plant materials with a high carbon content, scientifically called lignins (lignum means wood in Latin), are the slowest materials to decompose. These materials will make up the body of your compost. Anywhere from 60-75% of your compost material, by volume, should be high carbon materials.

2. Nitrogen

Nitrogen is typically added to compost as green material. Food scraps, grass clippings, and manure are all great sources of nitrogen. Green materials should make up 25-40% of your compost by volume. Many people worry about adding grass clippings and weeds to their compost because of the potential for weed seeds to end up infecting their gardens. However, in a properly managed pile, the temperature that the pile reaches –up to 150˚ F—actually kills all but the most xeric-loving seeds. These types of seeds are rare in comparison of other seeds and belong to certain pines, acacias, and other extreme pioneering plants.

3. Water

Water is extremely important to the health of a compost pile. Too much and you will create a pile of poison that will kill all of your plants. Too little and your pile will never decompose into compost at all. The best way to determine whether you have enough water in your compost is squeezing a handful of it into a ball. If it falls apart when you open your fist, you don’t have enough water. If you can squeeze water out, there is too much. 

4. Oxygen

Oxygen is perhaps the most important ingredient in your compost pile. The more oxygen your pile has, the better your compost will be. Regularly turning your compost heap will generally add enough oxygen.

How does compost work?

Just like other processes of decomposition, compost is created by bacteria and fungi. Whether you compost in the traditional way or use an alternative like vermicomposting, the real workers are the bacteria and fungi. In general, bacteria break down the nitrogen-rich materials along with simple sugars and acids, and fungi break down lignins, cellulose and other carbon-rich materials. There are hundreds of thousands of species of bacteria and fungi in soil and compost. Some of them are beneficial to your plants and others are detrimental. Luckily, they neatly fall into two groups, aerobic (oxygen lovers) and anaerobic (oxygen haters). When compost and soil has too much water, or when it is compacted by us walking and driving on it, it quickly becomes anaerobic and begins to smell bad. 

Swamps and marshes are anaerobic and produce ammonia, alcohol, methane and other noxious gasses and materials. If you have ever smelled the mud that rests on the bottom of a swamp or marsh, or witnessed foxfire (Scientifically classified as ignes fatui), then you have experienced an anaerobic environment. As enchanting as the glowing lights can be, most of the plants that we like to grow in our gardens and landscapes require an aerobic habitat, so overwatering and compacting will harm or even kill them. Never use compost packaged in a nonporous bag or container, as it will almost certainly have become anaerobic and will not only have no positive effect on your plants, but could inoculate your soil with dangerous bacteria. With a few notable exceptions, the majority of bacteria that cause food poisoning in humans are anaerobic.

In addition to creating an aerobic environment inside your compost that will encourage the growth of the bacteria and fungi that will have a positive effect on your garden and lawn, you must also be aware of the ratio of the fungi and bacteria themselves. Some plants, like many conifers, cannot grow efficiently without a symbiotic relationship with mycorrhizal fungi. Others, like broccoli and pioneering plants, need fewer fungi in the soil. Still other plants, like corn and tomatoes, need an even balance between fungi and bacteria. When soil is tilled too often, it can harm or even completely destroy the fungi in the soil, which in turn can make it less fertile for the seeds that you are planting. On the other hand, tilling before you plant broccoli might be beneficial. Knowing the needs of the plants you are working with and providing for those needs with the compost you create is fundamental to being able to successfully garden. Finding out which plants have similar needs in regard to fungi and yet complementary needs in regard to nutrients can optimize companion plantings.

When you start your next compost pile (or piles), take into consideration the plants that you are going to use it on. You might have three or four different mixtures that will contain and promote different ratios of fungi to bacteria. Remember, your plants don’t receive nutrients from the soil itself, but rather from the symbiotic relationships that they have with bacteria, fungi and other microbiology in the soil.