The Ultimate Guide to Building & Using a Three Bin Compost System

Do you have a large garden or generate a lot of organic waste?

If so, it might be time to consider a three-bin system and take your composting game to the next level.

The three-bin composting method comes with a number of advantages. It makes the turning process easier and is able to cope with large amounts of material.

(My own three-bin system deals not only with the waste from a large garden but also much of the organic waste from two neighbors!)

The bins are also far neater than the traditional compost pile, making them a great upgrade from a messy compost heap.

True, it can be a fair bit of work – at least when it comes to turning – but I’m currently experimenting with a way that could cut that work in half.

Let’s explore the pros and cons, how to build them, and how to use them so we can see if a three-bin compost system would be right for you.

What is a 3 bin compost system?

The three-bin compost system is a straightforward composting method that consists of three compost bins arranged side by side.

These bins can either be open or enclosed, depending on your preference.

The main purpose of this system is to facilitate the process of turning the compost from one bin to another, allowing for better aeration and decomposition.

There are variations on the three-bin system. Some systems use more bins, and the additional turning can speed up the composting process. Other systems use gravity to make turning easier.

We’ll cover these in more detail later in the article.

Pros and cons of a 3 bin system. 

Pros

High capacity

If you use a pallet bin system, you could end up with 24 cubic feet of space even before you start piling organic material above the top of the pallets.

What’s more, organic material shrinks rapidly in the compost heap. As you add material over several weeks, the material you have already added is sinking down.

That means you can add an awful lot of garden waste!

Ideal for hot composting

If you have reasonably sized compost bins, it’s quite easy to get your compost hot.

The insulation in the outer layer traps heat in the center of the pile, which makes it easier for thermophilic bacteria to thrive.

When you turn the compost heap, especially if you do it correctly, you ensure that bacteria get fresher material to decompose and introduce more oxygen into the heap.

Still, it’s worth bearing in mind that size is not the only way to insulate compost, and turning is not the only way to introduce oxygen.

Always have compost at different stages

One of the best things about having multiple bins is always having compost at three different stages.

You have one bin which is being filled with organic waste from the garden, one which is in the cooling or maturing phase, and one which is ready to use.

Convenience of turning

Turning a compost pile is a lot of work. 

You have to pull the pile apart, mix it up, then rebuild it. As you do, you have to try and shape the compost pile so it doesn’t spread everywhere, losing the value of insulating outer layers.

In contrast, with a three-bin system, you simply turn one bin into the other. The walls of the heap hold it in shape, which gives you one less thing to worry about.

Cost-effective

If you construct a DIY system, the cost can be very low! Pallets are often free or very low cost, and you only need to buy screws and brackets (or even some wire. 

Purchased systems cost a bit more, but you do get a lot of composting capacity for your money. 

Easy moisture monitoring

One problem with a standard, standalone compost bin is that you don’t know what is going on deeper in the compost bin.

You can see what is happening at the top and at the bottom, but it’s difficult to monitor the middle!

As a three-bin system usually involves turning, you can more easily monitor moisture levels and add water if needed.

Cons

Size

Keep in mind that the suitability of a 3-bin compost system depends on your garden’s size and the amount of waste generated. 

A 3-bin setup occupies more space than a single bin system and requires a substantial amount of waste to fill larger bins.

If your garden produces limited waste, you may want to reconsider the need for a 3-bin system. Instead, a small insulated compost bin could be more appropriate, as the insulation helps maintain a warmer temperature compared to an open bin system.

Effort Involved

Though a 3-bin system is easier to turn than a traditional compost pile, it requires more turning compared to a single bin system.

However, there are variations in the system that can help reduce the amount of work involved.

Setup

Setting up a 3-bin system may take slightly more effort than a single bin, but it’s crucial not to overstate this.

With a pallet system, you can construct a bin in under an hour and add more as needed. Alternatively, if you purchase wooden compost bins, they can be assembled in just a few minutes.

Aesthetics

Although a 3-bin system presents a neater appearance than a traditional compost pile, it may not be the most visually appealing addition to your garden.

If aesthetics are a priority, consider opting for a single bin system or a concealed compost pile instead.

Setting up a three bin system

Location

Location

When choosing a location for your 3 bin compost system, consider the following:

1. Place it close to where most of your gardening activities occur. In large gardens, the center of your beds might be ideal.
2. Ensure easy access to a water source for adding moisture when needed.
3. Prioritize proper drainage to avoid water pooling at the bottom, which can lead to anaerobic composting.
4. Select firm ground to prevent the bins from sinking or appearing unattractive over time.
5. Opt for a sheltered spot to protect the compost from drying out due to wind.

While it may not always be possible to find the perfect location, consider these factors for optimal results.

See more: Siting a Compost Bin

Build options

There are many ways to make a three bin system, and you are only limited by your imagination. In this section we’ll cover some of the most common.

Pallet Bins

For a quick, inexpensive option, build pallet bins. Keep in mind that they have a shorter lifespan, usually a few years.

As the pictures below show, they do deteoriate over time!

However, they are quick and easy to construct, and for the limited amount of time and effort that goes into making them, four or five years of use is excellent.

Here’s a tutorial on how to build your own pallet bin system…

Solid panel system

If time and money aren’t an object, you might want to construct a more elaborate system.

I would suggest a cover to stop rain getting in and forcing oxygen out of the compost.

I’d also suggest sliding wooden dividers between bins  This can make it easier to turn the compost from one bin into the next bin. 

You do need to choose between solid sides and sides with holes in them. There’s pros and cons to both. Solid sides add extra insulation, while sides with holes allow for improved airflow. They both work, so don’t worry too much about it. 

Wire panel system

Wood is expensive. 

To cut costs, replace wooden sides with wire panels while maintaining a frame. 

Alternatively, you can make a very system by placing stakes in the ground and stretching wire around the stakes.

Again, these options are great for airflow but not so good for insulation. 

Bought system

Finally, you can buy a system. The best purchased bins use sustainable treated wood, so they will last longer than a pallet bin. 

What’s more, it’s not a lot more expensive than a home-made system when you take wood and labour into account.

Three or four sides?

You also need to decide if you want three or four sides on your pallet bin. 

If you do decide to use four sides, then you want to be able to remove the front side to allow you easy access. I used a hinge for mine, but you could also fix them with wire or twine. 

A front panel does help keep the compost neat, but the bins work fine with three sides too. 

Size

You can compost with any size bin, but if you want hot compost in an open topped bin, bigger is usually better.

I’d suggest at least 3 feet (1 meter) in length, width and height. 

Rodent proofing

If you are concerned about attracting pests, consider using rat or mouse proof mesh along the bottom of the pile and across any holes. 

Learn more: Mice in Compost | Rats in Compost

How to use a 3 bin system

The basics

In many ways, using a 3 bin compost system is no different to any other form of home composting. Still, let’s walk through the process.

First, before adding material, you might want to consider putting a layer of sticks and twigs down. This can help trap air in the bottom. 

Then you want to include both brown (high carbon) and green (high nitrogen) materials.

You can see some examples below, or check out our C: N ratio tables for a longer list.

I’d also suggest including some dry bulking agents to ensure free airflow in your compost heap. 

You can mix the materials together, which is the optimal way to combine green and brown materials. However, most people add them in layers, as the convenience outweighs the optimization. 

(Both methods produce good compost.)

Once established, you should monitor moisture. This is hard to do when the bin is full, so the best thing to do is check it as you turn it. 

The compost should feel like a wrung out sponge. If it is drier, spray each layer as you turn it. 

Turning the compost sometimes helps resolve issues with excess moisture. However, you can also choose to add dry brown materials to absorb the moisture. 

Bear in mind that this may mean the composting process takes longer, as new brown materials will take longer to decompose than the rest of the compost heap. 

Build the compost heap in one go, or add over time?

Some guides will tell you need to add all the material over several days. That’s a lot of material, and for many gardeners it’s not realistic. 

Fortunately, the three bin system works just fine when you add material over time.

Turning in the three bin system

Turning: Traditional method

In the traditional system, you fill one bin with material.

The bin should heat up over time.  When that starts to cool down, you turn the compost into the second bin. This will usually heat it up again (you can help this with a device like the Ejwox compost aerator.)

When that has cooled down, you turn it into the third bin and leave it to mature.

Turning: My revised method

Some experienced composters use a single turn method, and that can yield great results. So this year I am experimenting with a one turn method. 

First, I’m going to fill up the middle bin with compost material. When I’ve used up the mature compost, I’m going to turn the middle bin into the end bin, and then fill the middle up again. 

While I do that, the bin on the end will be maturing. When that compost has used up, I will turn the middle bin into the first bin, and start all over again. 

The No Turn method

Joseph Jenkins, author of the Humanure Handbook, is a proponent of a no-turn method. By using bulking agents to trap air in, and straw to trap heat in, he simply builds a compost heap and leaves it to mature. 

I think this is viable (and my hot bin works with no-turning.)

I do sometimes use straw. In fact, in the picture below you can see how I am using straw with a new compost heap I’ve just started.

I left the top open when I took this picture, so you can see the grass and sawdust I added poking through, but after that I covered the top with more straw. As I add more material, I’ll push the straw back along the sides of the pallet.

However, the downside I can see with no turning is that you can’t check the moisture level of the compost heap. 

I actually combine his method with turning, so I use straw while I build the compost, and then scoop it aside when I turn it.

I’ve found my compost to be too dry several times on the first turn, and have added water accordingly. However, I’ve never needed to do this on the second turn.

Variations on the three bin system

Three bin system on a slope

One variation involves placing the bins on a slope. The first bin is the highest, with the others placed below it. The gravity then helps you turn the compost into the next bin. 

I’d love to try this, but I don’t have an ideal location on a slope!

Staggered height bins

This variation features bins with different heights, which can help accommodate varying levels of compost material.

The tallest bin can be used for collecting new materials, while the shorter bins are used for more mature compost.

Two bin compost system

You can also use a two bin compost system. With this system, you fill the first bin up with compost material. When it cools down, you turn it into the second bin where it can heat up, cool down again and mature. 

The disadvantage here is that you don’t always have mature compost ready for use. That’s in contrast to many solid sided compost bins, as you can usually access the bins from a slot at the bottom. 

Wrapping up

It’s worth taking the time to think about the system before you build it.  

After all, you could be using your three bin compost system for many years to come. 

Once you do have it set up, you’ll find that you’ll be able to process large amounts of garden (as well as other materials!) – and will get plenty of compost for long term soil benefits. 

I hope you have as much fun with yours as I have had with mine.

Now read…

How to Use A Compost Bin (The Only Guide You’ll Ever Need!)
How Do Compost Bins Work