Hi Mark,

Thank you for reaching out to the UVM Extension Master Gardener Program with your question! You’ve got some excellent questions concerning compost bins, so let’s get right to them.

-Should the bin sit on the ground or be elevated to allow air flow from underneath?

Yes, definitely set your compost bin(s) solidly on the ground. By keeping it on the ground the annoying big critters (like skunks and racoons) will have a much harder task accessing the contents from below and it will make it easier for the “good” little critters (like worms, microorganism, and other insects) to gain access to help with compost decomposition. Having it firmly on the ground should also help with heat retention and better drainage.

You might opt for a layer of hardware cloth on the bottom (and up the sides a bit) to deter the bigger critters if you have those concerns. Or sprinkle red pepper around the base of the compost bin if you find later on you’re having an issue. They learn quickly it isn’t a pleasant place to hang out.

-The sides will be constructed using 4" wide slats. Is there a recommended spacing between the slats?

There really isn’t a minimum or maximum slat spacing recommendation. This is more of a style preference. You could opt for adding hardware cloth between the slats to contain more of your compost within the bins (if you prefer a tidy looking compost set up) but it isn’t required.

Some 3x3x3 bin designs I’ve seen have a ½ inch slat spacing if that’s any help. And some have no side on one end. Some use pallets with very wide openings. There are so many variations! Successful compost bins can vary and all can work great. Build what will work best for you. But remember, it’s what you put in the compost that counts.

-Should the bin have a cover? If so, should it be solid or spaced like the sides?

In our climate, I would/and do cover my compost with a solid cover. This will allow you to manage your compost during extreme weather. You’ll be better at protecting the pile from becoming waterlogged by heavy rain or snow and maintaining necessary heat for decomposition during freezing winters. A cover can also prevent nutrients from leaching. It’ll keep the pile from drying out too much in summer as well.

-Lastly, do you recommend covering all spaces with hardware cloth?

I think I’ve covered your hardware cloth question, or at least I hope I have. It’s really up to you.

And just in case I’ve missed anything, I’m going to leave you with additional resources, below.

Resources:

Composting Tab, Resources Page, UVM Extension: https://www.uvm.edu/extension/mastergardener/gardening-resources 

3-Bin Composter: Do-It-Yourself Compost Bin Instructions, Wisconsin Horticulture, Div. of Extension: https://hort.extension.wisc.edu/articles/wood-3-bin-composter-do-it-yourself-compost-bin-instructions/  

How to Build a Compost Bin, MU Extension: https://extension.missouri.edu/publications/g6957  

Making Compost from Yard Waste, Virginia Tech Cooperative Extension: https://www.pubs.ext.vt.edu/426/426-703/426-703.html  

I do hope you’ve found this information useful.