How to Compost: Browns & Greens

The common advice for making compost is that you should use the correct ratio of browns and greens. Why is this important? What is the correct ratio? Are dried green grass clippings, a brown or a green? Good questions that will help you understand how to compost.

Browns and Greens – What are They?

In the simplest form, the terms are quite descriptive. Browns are any plant material that is brown, and includes fall leaves, dried grass, wood products, paper and straw. Greens are – you guessed it- green. It includes fresh grass clippings, freshly picked weeds, plant clippings and most kitchen scraps.

Calling composting ingredients brown or green is useful because it is simple for people to understand. However the terms are not always correct. It would be better to use the terms high nitrogen ingredient, and low nitrogen ingredient. The greens contain higher levels of nitrogen. For example, fresh green plant material contains high levels of nitrogen.

As the greens age they lose nitrogen and turn brown at the same time. Green leaves have high levels of nitrogen, but as they go brown in fall, the nitrogen levels drop. Wood products and straw have low levels of nitrogen.

So is manure a brown or a green? Based on color it is a brown, but based on nitrogen levels it is a green. As far as composting goes, it’s a green.

Other ingredients are also confusing. Alfalfa hay is ‘brown’ in color, but is considered to be a green since it contains a lot of nitrogen.

The bottom line is that the brown and green rule does not always work. Browns can be green, greens can be brown—it’s getting confusing! Stick with me, there is a simple solution.

How to Compost – the C:N Ratio

Recipes for making compost usually tell you to combine the browns and greens in the correct ratios. The recommendations usually go something like this:

The ideal C:N ratio is 30 parts brown to 1 part green.

Or

Use 6 inches browns to 2 inches of greens

Both of these recipes are simple to understand and simple to follow. Both are wrong.

The first one, “The ideal C:N ratio is 30 parts brown to 1 part green”, is just wrong. The author does not understand the term C:N ratio. It is not a ratio of browns to greens. It is a ratio of carbon to nitrogen. The carbon to nitrogen ratio in the compost pile should be 30:1, not the ratio of browns to greens.

The second composting recipe could be correct, but it is probably not. It all depends on which browns and greens you use.

Every ingredient has it’s own C:N ratio. For example horse manure is about 25:1. Fall leaves have a ratio of 30-80:1, depending on age of leaves and type of leaves. Reference 1 has a good list of C:N ratios for common composting ingredients.

The composting recipe of 6” green to 2” brown will only be correct if you use the right combination of ingredients – and that is not likely.

Why is the C:N Ratio Important?

Why is this ratio so important for composting? As discussed in Compost – What is Compost?, composting is a process whereby microbes degrade the organic matter added to the compost pile. These microbes have basic requirements for food, just like you and me. It turns out they grow best when there is a ratio of carbon to nitrogen of about 30:1.

The right amount of carbon and nitrogen makes the microbes happy, and they grow fast. Fast growing microbes means that the composting process happens quickly and the pile heats up to desirable temperatures. So for fast compost it is important to feed the microbes the right ratio of carbon:nitrogen.

What Happens if the C:N Ratio is Wrong?

The microbes will not be as happy, and they won’t decompose the organic material as fast. Composting takes longer and takes place at lower temperatures. However, it does happen.

You do not need the right C:N ratio to make compost. You only need the right ratio if you want to make it quickly!

The Reality of Composting

For the average home owner, it is very difficult to have the right ratio of material. Firstly, how can you figure out if your fall leaves have a ratio of 30:1 or 80:1? You can’t. Secondly, you rarely have the right ingredients available.

Most greens are available in summer. Most browns are available in fall. Some sources recommend holding the browns until you get enough greens and then using them. That is certainly an option, but it is a lot more work, and it needs more space. Who has extra space in their gardens these days?

The reality is that if you simply add your ingredients to the compost pile when you get them, and you turn the pile, you will make compost. It might be a slower process, but that is OK.

Don’t make composting complicated.

How to Make Compost Faster

Most home gardeners have more browns than greens, unless they bring in some manure or have a cow in the back yard. Most of the stuff you collect in fall and spring are browns. Based on the above discussions, too much brown results in a slow composting process. There is a simple solution to this problem.

The problem with too much browns is that the there is not enough nitrogen for all of the carbon. A very simple solution is to add some nitrogen fertilizer to the compost pile. Adding a handful of Urea to a pile of leaves will speed up the process. If you want to go 100% organic, use some fresh chicken manure or you can pee on the compost pile. Both are good organic sources of nitrogen.

If your compost pile starts to stink, you added too much nitrogen. It only takes a bit of Urea.

I stopped worrying about green and brown ratios a long time ago. I still ended up with compost.

References:

1) How to Compost – Carbon to Nitrogen Ratios: http://www.planetnatural.com/composting-101/c-n-ratio/

2) Photo Source: Peter & Ute Grahlmann