How Composting Works
& How to Make Compost

People are concerned about the nutrient density of our food. Some of the vegetables sold at grocery stores have lower nutrient levels than years past. Magnesium, Manganese, Selenium and other mineral contents are dropping. The alleged culprit? Depleted soils.

As it turns out, a significant proportion of agricultural soils are suffering nutrient deficiencies. It's a concern that highlights a basic reality in farming and agriculture: You can't keep removing, without also replenishing. We can work hard to grow spinach, kale or chard in an effort to boost our body's iron or magnesium levels. But as we work our little plot, year after year, consuming nutritious crops... we need a way to put it all back!

Nutrient Depletion: Imports vs Exports

Our planet Earth is a closed system. The water, carbon, oxygen and every other element must be recycled and reused again and again. If any given resource is consumed faster than it is replaced, we lose our sustainability. We could view our yards and garden areas in a similar fashion. Little islands. How much are we importing? What about our exports?

Fruits & veggies given to friends & family are exports. After we eat our harvest and expel waste through public sanitation systems, we are exporting nitrogen, phosphorus and lots of other minerals. If we bag our grass clippings and throw them out. If we put our kitchen scraps into the trash. If we throw our leaves out on the curb. Then we are exporting nutrients off of our lot. These are all outputs that will eventually need to be replenished. So we try to build fertility in our soils by importing fertilizers. Or we may buy bagged composts or manures.

What can be done to reduce our reliance on external nutrients sources? Nutrient cycling is the key! For example, lawn fertilization is a big industry in America. Does it come as any surprise when we think of all those grass clippings that are bagged and hauled off-site? What if we simply mulched those clippings? As those clippings break down, the nutrients are restored and suddenly our lawn doesn't need extra inputs!

DIY Compost Made in a Tumbling Composter
It's easy to make homemade compost by recycling organic waste from yard and kitchen scraps!

What is Composting & How Does it Work?

Composting is the mechanism by which a gardener harnesses microbes, worms or creepy crawleys and puts them to work. You can throw a pile of leaves in the woods and they'll break down naturally. But if you shred them, increasing surface area, the process speeds up. If you mix in some nitrogen rich grass clippings, the microbes go crazy. And if you mix and turn your pile, aerating it, the aerobic bacteria get hotter. Before you know it, you have rich, deep black compost (better than anything you'll find at a big box store).

Saving grass clippings is just one example. Think of all of those ways that you can harness the power of decaying organic matter. Cardboard scraps? Feed them to the worms and make your own worm castings. Autumn leaves? Let them break down and turn into leaf mould, a perfect garden mulch. Kitchen and plant waste? Compost that stuff and make your own soil amendment.

It's a double win! None of these materials need to get shipped off-site (which wastes resources). Once they've been decomposed, these can replenish your soils, reducing your reliance on fertilizers.

Composting Garden Weeds & Grass Clippings Into Organic Compost Fertilizer
Composting allows you to convert weedy plant waste into fertile organic matter.

Methods: How to Make Compost

COMPOST PILES are free and simple to set up. They take up the most space, occupying a 3 foot by 3 foot area. Manually turning them is more work and less efficient than tumblers. But if you have a large volume of organic matter, then this is an easy way to go. If you have lots of space, you could simply make a new pile every year. Once you have 3 or 4 piles, you can start pulling finished compost off of the oldest pile. And then you can just continue to rotate through them each year.

BIN COMPOSTING is similar to using piles, except the organic matter is contained within a raised bin. It's a little tidier than an open pile and it can be stacked taller, reducing the footprint requirement. There are many retail compost bin products on the market. Some are completely enclosed, while other might simply be an open topped cylinder or box. One popular DIY option is to stack wood pallets on their side in a box shape to create a makeshift compost bin.

Geobin Large Compost Bins at Community Garden for Outdoor Composting
These geobin composting bins allow several compost heaps to process at various phases of maturity.

LEAF MOULD is created by collecting autumn leaves and allowing them to slowly break down over the course of 1 to 3 years. This interesting variation on compost piles works best when you use only leaves. There's no need to turn the pile. The resulting product is an earthy rich leaf mould or leaf humus. Because you don't use weed seeds, it makes for a trouble free compost material. Just use caution if you have walnut trees in your property. Their leaves contain juglone, a chemical that is toxic to some garden plants like nightshades.

TUMBLER COMPOSTING employs microbes to do all of the dirty work. A tumbler requires less space than conventional piles, and it is much easier to turn. The process is fast and efficient. Of course, buying a good tumbler is going to cost you. I prefer compost tumblers when processing food scraps that might otherwise attract vermin. If you optimize the contents, you can achieve high temps which help to destroy weed seeds.

VERMICOMPOSTING relies on worms for composting. Typically, gardeners will purchase special types of red worms like red wigglers. Worm bins require virtually NO space. Even apartment dwellers can compost indoors by using DIY tote worm bins. The end product is a pile of rich worm castings, often referred to as "black gold".

Vermicompost Worm Castings Harvested From Worm Bin
Composting with red worms is a great way to turn vegetable scraps into black gold!

Using one or more of these techniques will reduce your waste, and produce a free nutrient source for your garden. You'll create a cycle of sustainability. And you'll enjoy a greater level of self-sufficient independence!

Hot Composting vs Cold Composting

Compost piles, bin composting, leaf moulds, tumbler composting and vermicomposting are all effective methods for breaking down organic matter into nutrient-rich compost. But these methods can be divided into two basics categories. Depending on the compost system and the way it's managed, a method might be considered either "hot" or "cold" composting. Each approach has unique advantages. Depending on your goals and lifestyle as a gardener, you can select the compost technique that works for you.

HOT COMPOSTING: Hot composting is an aerobic process that can break down organic matter at an incredibly fast rate. For the process to work well, your compost materials need a proper balance of nitrogen, carbon, water and air (oxygen specifically). This environment promotes the rapid growth of aerobic bacteria producing water, carbon dioxide and lots of heat.

Hot composting can cycle through various phases. During the composting process, microorganism populations shift in dominance from psychrophilic to mesophilic and then thermophilic. Ultimately, once your compost pile reaches 115°F it begins to enter hot composting territory. If you properly maintain it, you can easily see temperatures of 130° to 140°F. The compost may even reach 160°F which easily kills pathogens and most weed seeds.

A balanced, large compost pile can be hot composted if you are willing to turn it over regularly. This maintains good pore spacing, allowing oxygen to reach those heat generating aerobic bacteria. Tumbling composters are prime examples of hot composters. By regularly tumbling them on a daily basis, you can churn out a batch of finished compost in as little as 3 weeks!

Insulated Hot Compost Tumbler 152 Degrees F in Winter
This actively maintained insulated compost tumbler reached 152°F despite Winter temps of 33°F!

On the other hand, if you have a large enough compost pile, its collective mass can create very hot temperatures without any need for turning. Another tip for achieving hot compost temperatures is to shred your organic matter into smaller particle sizes. Smaller particles have increased surface area. This speeds up rates of bacterial colonization resulting in higher temps.

COLD COMPOSTING: Cold composting is a more all encompassing term. This merely indicates a form of composting that occurs at lower temperatures. Some people associate cold composting with anaerobic processes. But this is only one of many forms of cold composting. Any type of decomposition or organic breakdown that occurs at temperatures below 100°F can be classified as cold composting.

Cold composting might occur intentionally, by design. Vermicomposting is a form of cold composting done by worms. They do the work of breaking down soft organic materials without generating lots of heat. The creation of leaf mould is also a form of cold composting. Rather than relying on bacterial degradation, the pile of brown leaves is primarily broken down by fungal decomposition.

Sometimes a compost pile will switch to cold composting processes in response to environmental limitations. If a compost pile is too small, it may simply lack the mass needed to achieve hot temperatures, especially when ambient temps are low. Larger particle sizes reduce rates of decomposition which yields a cooler pile. Limitations in water or nitrogen can also slow down the composting process. Or too much water can create anaerobic conditions which foster the growth of putrefying bacteria. This results in a colder compost pile that produces excess methane and does not get as hot.

Video: Making Hot Compost With a Tumbler!

For many years I was able to recycle all of my kitchen scraps by using this compost tumbler.

Using a Compost Tumbler

HOW TO LOAD A COMPOST TUMBLER: The compost tumbler I've used for years is the Jora 70 (JoraForm JK270) a 270 gallon insulated tumbler. You can read my review here. Each of its two chambers holds 35 gallons or a little less than 5 cubic feet. The idea is to load a single chamber until it is fairly well filled up. Then stop adding to it and begin using the second chamber. By the time that second side is filled up, you might find that the first batch is already complete! Of course, you need to spin it daily. And there are other factors to keep balanced as well.

WHAT TO ADD TO YOUR TUMBLER: Expect most websites to share some sort of ridiculous formula of "brown" and "green" ratios. To get a good hot compost you need to have an adequate balance between nitrogen (green) and carbon (brown) materials. It's completely impractical and needlessly overcomplicated to keep track of green / brown ratios. In general, just add your organic waste. Add all of your kitchen scraps. Add all of your garden weeds. Just don't include mature seed heads if you can avoid it. If possible, include woody clippings from your shrubs and trees.

Chipping Tree Branches to  Make Wood Chips for Composting in a Tumbler
Freshly chipped wood pieces greatly enhance the quality of the compost in my compost tumbler.

THE TRICK TO AWESOME COMPOST: Particle size makes a big difference in a tumbler. Chop up your weed clippings before dropping them in. I've always gotten excellent compost texture by including small wood chips from branches that I've trimmed off of my trees and bushes. They offer plenty of carbon and help with aeration due to their loose open structure.

One secret ingredient which has supercharged my compost is coffee grinds. Coffee grinds already have a small particle size. And they have plenty of nitrogen for a nice hot compost pile. If you can get them in large batches from work or a coffee shop, you'll be amazed at the results!

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