Should You Put Your Compost Bin on Slabs?

Once you’ve decided to start composting, one of the first things you have to determine when you begin is where to sit your bin. Placement is crucial and may be quite tricky when you have limited space. When you’re using a compost bin, you might be wondering if you should place it on the ground or slabs. 

You shouldn’t put your compost bin on slabs if you can avoid it, as the leachate from the compost can stain the slabs. Concrete slabs might get degraded by the leachate over time. Compost bins on slabs also need to be monitored closely for compaction and moisture levels to keep the compost healthy.

In this article, I’ll explore what compost bins should sit on, the many issues with placing them on slabs, and how to fix them. I’ll also explore the best composting units to use if you have to place yours on slabs, so read on. 

What Should a Compost Bin Sit On?

When selecting a compost site, you should consider how close the bin is to your house and water source. 

Your compost bin should sit on the ground. This allows organisms like microbes, worms, and fungi to enter the pile. These organisms will help break down the organic matter, accelerating the composting process. The ground will also absorb any leachate, so you don’t have to worry about stains.

A simple compost bin made of wooden pallets arranged in a box shape is the easiest and cheapest type of compost bin to make. The bin doesn’t need a base, as it can directly sit on the ground. This location will allow beneficial insects to climb in and help the bacteria break down the feedstock. 

If you’re worried about animals digging under your bin, you can line the underside with chicken wire or wire mesh with small holes to deter rodents and scavengers. This mesh will ensure that the insects and microbes can get in while keeping other pests out of your bin.

Issues of a Compost Bin on Slabs & How to Fix Them

If you place your compost bin on slabs, you might face several issues. But if space is a premium and you don’t have a choice, you don’t have to be discouraged. Your compost doesn’t have to touch the ground to be healthy.

Here are some common issues related to placing your bin on slabs and how you can work around them: 

The Leachate Will Stain and Degrade the Slabs Over Time

The biggest concern with placing your compost bin on slabs is that the leachate from the compost will stain the slabs and degrade them over time. 

Leachate refers to the liquid produced when water drains through the compost pile while composting. Leachate may also be produced by the rapid decomposition of kitchen waste and other greens, resulting in the production of excess organic acids. 

The liquid itself is useful as a soil drench and typically enriches any soil on which the bin is sitting. However, when you place your bin on top of slabs, the chemical composition of the leachate will affect the integrity of the slabs over time and will definitely stain them. 

If you must place your bin on concrete, it is good to use a collection tray under your bin that is easy to drain. If you have a small bin, you can simply lift it, but if your bin is large and heavy, you might want to consider an elevated bin. An elevated bin lets you collect the leachate easily without having it stain your slabs.

Your Pile Might Compost a Little Slower

Most places recommend placing your compost bin on bare earth to allow microbes, fungi, earthworms, and other insects the opportunity to enter your pile. These organisms speed up composting by eating and processing the organic matter in your pile. 

While this might seem like a significant advantage, the speed of composting isn’t that improved. Additionally, worms and microbes tend to colonize compost piles regardless of whether you place them on the ground or not.

To get the same results, you can always add worms to your compost later after setting your composting unit up. To introduce more microbes to your compost, you can use a bio-activator. 

Bio-activators refer to the microorganisms and bacteria naturally present in organic compost. Depending on the size of your pile, you can add a shovel full or a few shovels full of potting soil or compost from previous batches. You can also use shop-bought compost as a bio-activator as long as it doesn’t have any additional fertilizer. 

The Compost Might Compact Easily

Compost that is piled directly on the ground has room to spread as it needs to and expand as it needs to. Aeration is easier in a pile that you place on the ground. 

However, if you’re putting your compost in a contained bin, especially one on a firm base like concrete slabs, the compost will compact easily. 

You may address the issue of compaction efficiently by turning and aerating your compost on a regular schedule. You should turn your compost once every 3-4 days, especially in the first two stages of composting, which can last about 2-3 weeks.

You can also add more browns to your compost as the twigs, sticks, and other woodier materials break up the compaction and incorporate air pockets into your pile.

There Might Be Some Waterlogging

When you place your bin directly on the ground, the soil easily absorbs any excess liquid or leachate. Even if your bin has a base placed on top of the ground, the drainage and ventilation holes will let the excess liquid seep through into the ground. 

However, concrete is a less forgiving material and might trap the excess liquid inside your bin. If your compost gets too wet, it could slow down the decomposition by drowning all the aerobic bacteria, resulting in unhealthy compost that could make you sick.  

The best way to prevent this is to turn and aerate your compost regularly and maintain the balance of browns to greens at 3:1. You should also ensure that your bin has holes on the side as well as on the bottom for drainage, as this will allow more avenues for the water to drain. 

Best Composting Units to Put On Slabs

Not everyone has the yard space to set up a composting unit on the ground.

Here are a few different types of composting units that you can consider if you have to sit your bin on slabs:

Use a Vermicomposting Unit

Vermicomposting involves using worms as the primary decomposer in a composting unit, not just additional, incidental decomposers like in a traditional composting bin. 

Vermicompost bins are ideal for small spaces as the bins can be just about any size, and you don’t need to place them on the ground. In fact, vermicomposting units need to be raised off the ground to allow airflow, and you can easily place a tray underneath to catch leachate. 

The important thing about placing a vermicomposting unit is to put it somewhere shaded. The base of the compost bin does not matter. 

Consider Tumbler-Style Units

Compost tumblers are usually elevated on stands and are the most common type of composter available. You can even make your own using an old plastic or metal garbage can and some wood to make a stand. 

These bins make aerating the compost much more manageable as most tumblers are designed to be rotated on their stands. 

The only disadvantage with these types of units is that they can be hard to harvest from and might get blown over in windy conditions. So while you may place these bins over concrete, you should ensure that you shelter them adequately.  

Consider a Dalek Bin

Dalek bins refer to bins shaped like a ‘Dalek,’ with a wide base and narrower tops. These bins make good compost because the design allows the compost to reach high temperatures very quickly. These bins are also sturdy and unaffected by the elements.

These bins can be placed easily on concrete slabs as the composting process is rapid, and very little leachate is produced due to the high temperatures inside the bin. The one disadvantage of the Dalek style bin is that the compost is hard to turn, but using a specialized turner should work well. 

Use a Bokashi System

Bokashi refers to a Japanese method of composting that uses a special bin. This bin has an airtight container, a drain, a filtering tray, and a cup for collecting the ‘compost tea.’

The system uses bokashi bran instead of browns as part of the feedstock resulting in fermented compost that you may use as fertilizer and a liquid compost tea. The bin can be placed on any surface and is convenient to use if a bit expensive to set up. 

Final Thoughts

You should avoid putting your compost bin on slabs if you can, as the leachate can affect the integrity of your slabs and will definitely stain it. The compost can also get compacted and waterlogged. 

If you can’t change where you’ve placed your bin, you should add a tray to collect any leachate, turn your compost regularly and add enough browns to balance the moisture levels in the bin. The best bins to place on top of slabs include vermicompost, bokashi, tumbler style, and Dalek bins.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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