Cold compost is a process of helping organic matter to decompose over time and without the use of heat and thermophilic microbes.
Homemade compost is usually cold composting. It’s called that because it doesn’t utilise thermophilic microbes to rapidly decompose organic matter. It doesn’t necessarily include heat.
My article on hot composting discusses how to build and maintain a hot compost. This article is about cold composting because it’s the most common for home gardeners. Instead of using heat, we use time.
It takes more time to transform organic matter using cold composting methods. There are heaps of ways to compost. I’m going to share one way and include some helpful tips.
Making cold compost takes time
Compared to the 4-6 weeks for hot composting, making a cold compost can take 6-12 months or more. There are ways to speed it up and here I’ll share some methods for doing just that.
Use smaller pieces
Generally, the smaller the pieces the better. Given the same volume of matter, smaller pieces have a larger surface area than larger pieces. Therefore, more microbes can inhabit smaller pieces that have the larger surface area. That means more effective decomposition.
Having said that, small pieces tend to pack down more readily… that can cause a lack of air flow through the pile. Read on…
Reduce hiding places
Compost piles with sticks and large pieces can create caves and hiding places for rats, mice and snakes. If you can’t reduce the size of sticks, then make sure you push organic matter into any pockets and caves that may form as you create the pile.
Ingredients in a compost pile
Most healthy organic matter can be added to a compost. Diseased ingredients shouldn’t be added to the pile.
Flora based kitchen scraps, lawn clippings, tree prunings, green or dried leaves, coffee grounds, egg shells etc are all excellent ingredients for a cold compost pile.
Lawn clippings without lawn seeds… otherwise we’re likely to introduce lawn seeds into our compost. The same goes for weeds. Weeds are fine, but keep out the seeds.
Green leaves are also fine as are dried and brown leaves, and fine mulches like sugar cane mulch.
Air is a key ingredient in cold composts. We might not turn our cold compost as we do our hot compost, however we still need to allow air into the mix. We can do this by fluffing out the ingredients we add and mixing the ingredients as best we can.
Don’t add clumps of lawn clippings for example as it’ll end up anaerobic and full of pathogenic microbes.
Water is another key ingredient. We add enough water to moisten the ingredients. Microbes tend to flourish in moist environments so a moist cold compost pile will benefit them and you.
Check for hydrophobic ingredients. Sometimes lawn clippings or dried leaves that have sat and started drying out can become water resistant. Read my blog on hydrophobic soil to find out more.
Green and brown have different functions
Green ingredients such as lawn clippings and green leaves are the nitrogen base for the microbes. The browned and dried ingredients such as dried leaves and mulch are the carbon base.
Generally, microbes need more carbon than nitrogen so we need to add more of the brown relative to the green. The ratio of 3 carbon to 1 nitrogen tends to work well.
Method of creating a cold compost
Mix the ingredients as best you can. Layering ingredients works but thorough mixing works better.
If you’re going to choose to layer the ingredients you might want to start with a carbon ingredient like dried leaves or mulch followed by a nitrogen ingredient.
Add water as you build the cold compost pile. The outer layer should be a carbon ingredient to reduce vapourisation of nitrogen from the pile.
Maintaining a cold compost pile
Regularly check the compost pile. Check the smell. If it smells bad, it probably is bad. Compost piles shouldn’t stink… unless you’ve added manure in which case the stink should go within a few days. But if your compost pile becomes smelly it’s a sure sign pathogens have taken over the pile.
Check the air flow. An aerobic compost pile smells earthy and has an abundance of life within it: worms, micro arthropods and little bugs and trillions of microbes. A smelly compost is likely to have reduced or no airflow. Increase airflow by lifting and fluffing parts of the pile with a garden fork.
Check the moisture levels. It shouldn’t be too wet. That means if you’re hand looks wet after handling the compost, it’s too wet.
You can continue to add to a cold compost and this is best done at one end of the pile. That way, you can start harvesting compost from the opposite end when it’s ready.