I took a long drive in -18F temps today to pick up 6 1/2 pounds of red wrigglers. My trip took me almost to the Canadian border, so guessing that it doesn't get much colder than this for raising worms in the US.
I have held off posting about this until now because I was hoping to get some photos to go along with my description. Unfortunately the weather was not conducive to a tour today so that did not work out, but I did get some great information from the worm farmer.
disclaimer- I am not going to mention her name here because a) she does not do online sales and b) she will only ship on a case-by-case basis and only via one small, regional carrier who delivers within a limited area (she does not ship via USPS or Fed X or UPS), and she definitely does not ship in cold weather, which is one reason I drove to pick up worms from her today.
With that said, she has been raising and selling worms for over 30 years so she has had plenty of time to figure out how to do it in our cold climate. She does not have the worms in her house, nor does she have a heated space for them. She also does not use CFT's.
What she does is this- she uses 150 gallon rubber stock tanks (livestock watering troughs). It sounds like her bedding is peat moss with lime added, along with some sand and blackstrap molasses, which she then sprays down with "worm juice" to get the microbial activity off to a jump start. She keeps two of these bins in an unheated garden shed- a "very heavily insulated" garden shed which does have electricity and in "very cold weather" ("around" 0 deg F and lower) she will run a small electric space heater to supplement the heat which is created by the worm bins themselves. She has more than two bins but the others are kept offsite. Each of her two 150 gallon stock tanks full of worms and bedding can process as much as 200 pounds of food waste each month if kept in a cool space (approx. 6 1/2 pounds per day on average) generating quite a bit of heat in the process. If kept in a warm space the feeding capacity drops. She told me that if she keeps up with the feeding schedule the worms stay pretty active- and judging by the size of the worms I got from her (lots of juveniles, less than 3 months old) they have been doing a lot of breeding and growing since the beginning of winter. I guess then, conversely, if she doesn't get out there to feed them as much or as often they are less active. She did not say whether she ever has die offs in the winter and I never got around to asking her directly, but it does not sound like she does.
Since my husband and I lack heated space for a lot of worms we have been discussing the possibility of building a small room inside of our large unheated barn which we could insulate and then heat using a small portable heater of some sort. As soon as I mentioned that to the worm farmer she immediately said "yes, build a room in a room" kind of thing. Now that I have met with and talked with her and seen her worms I think this is the way for us to go, at least for the short term. Much cheaper than trying to insulate the entire barn, and exponentially cheaper than putting up a heated building. This will buy us some time to start developing a market for our worms and see how we do before committing a lot of capital to buildings and infrastructure. I am still planning to fill as much space in our basement as possible with some small CFT bins that we are working on building but now I know that we have room to expand on a budget, which is very reassuring.
Hope this helps someone else who is in the planning stages for cold climate worming.