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[Originally found here: http://www.motherearthnews.com/organic-gardening/winter-worm-composting.aspx]

Even in the heat of summer, it’s not to early to consider ways to keep our garden friends, our composting worms, fully employed over the winter months. For now, use that vermicompost for some worm “compost teas” to help your gardens with the stress of this summer’s heat. When cold weather comes, gather your materials and try overwintering your worms outside.

Cold weather (remember that?) will definitely slow the activity of a worm colony. Although my experience is that worms can be incredibly hardy, there’s no reason to miss a beat over the winter. The two key factors are shelter and heat.

Last winter I chose had to replace my compost bins cause they were rotten. They were oak pallets and they had lasted about seven years. I took the old pallets out, but wanted to level the site, so I started digging. What I found was a very rich layer of vermicompost between and under the pallets. Remember, I’ve been filling my bins with worms and managing for their happiness for the whole seven years.

I ended up with a level site and nine wheelbarrows full of vermicompost! As I shoveled the black gold aside, I tried to put the material with the most worms farthest from the compost bin pad. I spread the vermicompost on my garden and mulched it for the winter.

What was left over was perhaps three wheelbarrows of finished vermicompost and most of my worms. I covered the pile with some clear plastic greenhouse glazing. I never stopped putting my household food scraps on the south side of the pile. I simply came outside, lifted the plastic and a layer of straw and threw the scraps into the pile. What happened was that I started an active composting pile. There was enough food coming in, getting mixed in and covered to get hot and keep the whole area well above freezing. The winter sun helped warm the pile through the clear plastic. On cold nights there was condensed moisture on the inside of the plastic but the pile was plenty warm enough to keep going. 

The worms were hanging out at the edges of the pile, staying warm and well fed. Although last winter was mild, this strategy will work well as far north as Minnesota, as I found out on a tour of compost education programs to St. Cloud in 1993. I visited Compost Guru, Jim McNelly (founding board member of the U.S. Composting Council) as he brought me in to educate in the schools there. He had a busy worm colony in a small black plastic compost unit outside his house in a tough winter.

Top photo: On the left is the windrow full of vermicompost that I harvested from the dark flat area on the right. Notice the clear plastic covering the pile, the pallets that will become the next bin and the stored bags of leaves.

Lower photo: The worms are hard at work under the clear plastic and the straw layer. The 2 x 4’s are not a part of the system, just left overs from the compost bin being built in the background.

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This is a great example of how simple you can make a vermicomposting system.  With a nice sized hole and enough straw plus a tarp, you can keep your worms alive and well through the winter.  I don’t know how they do it, but they do it.

I spotted a mouse sitting on top of my Worm Inn a while ago, and although he didn’t get in the system, it bummed me out.  It was my fault though, I didn’t have a nice layer of bedding covering the food scraps.  That’s the key with vermicomposting, whether it’s indoor or outdoor, is to always cover your deposits with plenty of bedding material.

Although it’s probably too late for me this winter, I’d like to try the outdoor method soon.  It’s hard to see the point though, with my main compost bin still cooking and handling all my scraps with ease…