Keith has been involved in the gardening and landscaping industry for the past 21 years. From a jobbing gardener to running his own landscaping services....
Green material for compost is the “magic sauce” that all compost piles need. While almost all materials will eventually decompose to make compost for brown materials this process can take many months or even years without the introduction of green material. This is because of their chemical makeup as green compost materials are high in nitrogen content, a crucial component for kick-starting the composting process.
What makes something a green material?
There is a lot of confusion over what represents green material. The label has traditionally been applied to items that are green, usually kitchen food scraps. However, in truth composting is about science and not labels. Efficient composting is about getting your carbon-to-nitrogen (C/N) ratios right. Therefore, instead of thinking in terms of color, the right way is to think in terms of attributes.
As such, green material for compost should be classed by its properties. For a material to be considered green it must be nitrogen-rich, have a carbon-to-nitrogen ratio of 30:1 (C/N) or less, and be wet as this provides moisture to the composting pile.
Of course, water can always be added to your pile so when assessing whether a particular material is green or brown, concentrate on the nitrogen content.
In practice, green materials are usually kitchen food scraps and growing materials such as grass clippings.
What are green compost materials for compost?
While the bulk of your compost pile is going to be brown material, the green material is the material that is going to help make the composting pile decompose at a more controlled rate. Below is a list of some of the most common green materials that you can use in your composting process:
- Meat and Fish*
- Kitchen vegetable scraps
- Grass clippings
- Coffee grounds
- Peanut husks
- Cow manure
- Soybean stalks
*Although meat and fish have high nitrogen contents it is not advisable to add these to your compost pile unless you know what you are doing. They attract vermin and give off a horrible stench when decomposing.
Green Materials in Terms of Compost Ratios
One of the most important parts of having an efficient and controlled composting pile is getting the correct carbon-to-nitrogen ratio.
The composting process is a chemical interaction that occurs between the carbon and nitrogen in the composting materials, which results in the formation of compost.
The ratio of carbon to nitrogen (C/N), as well as the amounts of water and oxygen present, determines the rate at which the decomposition process will proceed. Typically, the most effective C/N ratio for cold composting is between 30:1 and 35:1 (C/N) if cold composting and around 25:1 if you were hot composting.
Obviously, you will not achieve exactly the 30:1 ratio when building your compost pile but having an idea of what each class of green material holds in terms of nitrogen can help you get close enough to have an efficient compost pile that will produce finished compost in three to four months, or four to five weeks if you’re hot composting.
Carbon to Nitrogen ratios for Common Green Materials
|Materials High in Nitrogen||Carbon:Nitrogen Ratio|
|meat, fish soybean meal||5:1|
|vegetable peelings and scraps||20:1|
What can I use in place of green material for composting?
If you are struggling to put together enough green materials you have a couple of options.
Green material for compost is all about being nitrogen-rich so that the reaction taking place produces enough heat and allows the press to move through the composting stages.
The objective, therefore, is to get the ratio between carbon and nitrogen right. You can buy what are called compost activators/accelerators that will kick-start the decomposition process. You can add these to your compost pile to compensate for the lack of nitrogen.
If you prefer a more organic solution then horse or cow dung are both high in nitrogen. Just find stables nearby and I’m sure they would be more than happy to provide you with a few sacks full.
In areas where seaweed is abundant, you’ll have a virtually limitless supply of nitrogen and nutrient-rich green compost material. Due to its high nitrogen concentration, seaweed may help a compost pile heat up. To eliminate any salt residue, it is advisable to rinse the seaweed well before adding it to the pile.
Commonly asked questions?
Can green material help the compost pile on top?
The top layer of a compost pile should be brown materials, or if hot composting mixed brown and green. If you have further green materials to add to your composting pile put them into the center of the pile while turning. This will help avoid animals attacking your composting pile.
The exception to this would be grass clippings which you can put on top of the pile, but as a thin layer to prevent clumping.
Are grass clippings green or brown material?
Grass clippings have a high nitrogen content, around 20:1 (C/N) and are therefore considered a green composting material.
Many gardeners leave grass clippings directly on the lawn so that they can break down naturally and feed the grass. Caution should be observed though as this can cause fungal lawn diseases if are cannot get to the grass.
Add grass clippings to your compost in a way that maintains the carbon to nitrogen ratio of your pile. You can add grass clippings either on top of a layer of brown materials or completely mixed. Problems occur when they are put in an excessively thick layer which can cause them to clump together hindering airflow preventing oxygen from circulating and slowing down the decomposition process.
Can you have too much green material in compost?
Green material is nitrogen-rich. If you have too high a nitrogen content then the nitrogen is turned into ammonia gas and you can lose some of the nutrients from the finished compost. It also will give off a horrible stench.