QUESTION: Do compost bins need to be on soil? Can you put one on your patio or deck instead? – Richard D
ANSWER: Although it’s not required for your compost setup to rest on top of the soil, in certain circumstances it is preferable, though in others it does not make a difference. For one thing, if you are using a compost container that has a solid base, you can position it on soil or on concrete, as the compost won’t be coming into contact with what’s below its container anyway. It’s when your composting arrangement will not include a built-in base that it matters whether it will be located on soil, on concrete, or elsewhere.
Positioning your compost heap directly on top of the ground will allow insects to crawl up into the compost from the soil below, which is a good thing. These insects are beneficial to the health of your compost and will help to aerate the pile, speeding up the process of decomposition. That said, you’ll still need to use a material like wire mesh or hardware cloth as the base of your compost pile so that larger creatures, such as rodents, don’t follow the lead of the insects and climb up from the ground into your compost.
Another thing to think about is that if your compost is located too near to a tree, the tree’s roots can also infiltrate the compost pile by coming up through the soil—and they are likely to do so in their search for nutrients, which your compost materials are full of. The roots of the tree will be detrimental to the health of your compost and will inhibit your ability to turn the pile, so make sure if your compost will rest on the ground that you position it a good distance away from any trees on your property.
The final consideration is purely cosmetic. A compost pile that rests on concrete or another man made substance will inevitably stain whatever material is underneath it. The stain can decrease your property value in addition to being unsightly, so unless your compost situation comes with a solid base, putting your compost on soil is likely to be the best option for you.