Brice,

Not only will that work, but is in fact how a large number of worm farmers in adverse climates raise their worms. The ground help stabilize temperature and ensure adequate moisture without the need for constant watering. The major downside is the difficulty in ensuring adequate drainage, but this is not a huge deal.

A depth of 16-24" should be plenty and a good rule of thumb is at least 6" deeper than the frost line.

Looks like you will have to find another way to torture your worms ;)

Sorry for the delay in answering this.

I can tell you how I build them here. Also I can give my guess as the changes you should make for your are, but as for the extreme cold, I am so much further south I will not have a ton of experience on this.

Here our soil is a really compact clay that does not drain at all. One benefit to this is that moles and worms cannot burrow in or out very well as long as the topsoil is removed and the beds sit on the hard clay.

On our worm beds here at WormsEtc, the sides are made from 1/2" exterior plywood. We take the ground they sit on down to the clay, ie remove the topsoil. But the beds are not really below the grade, they sit just about on grade. Since you are in a colder area it may make sense to dig the worm beds down a little. When the beds sit on the level with the grade we don't have any drainage issues. If you dig them below you may have problems. If so then you might consider adding a perforated drain line at the bottom of the bed. Provably it would be best to cover it with sand and put landscaping cloth on top of that.