Composting in a bathtub could work. It would be best to figure out a way to do it year round. What are you going to do with your worms in the winter, or if it gets too hot? You can't just haul the whole thing inside.

Neither can you dump them into your garden. The worms you compost with typically are not the same worms found in garden soil. The worms in your soil probably will not like living in a bin.

Worm composting in a bathtub is pretty ambitious for a first time wormer. You may be better to start off with a much smaller inside bin and grow from there. It is less costly to make mistakes with 1 pound of worms than with 20 pounds.

As for bedding, you would use the same kind of bedding you would if you were composting in a smaller system indoors. The one difference being that you would want something you can obtain in larger quantities. Do you have a source of horse manure nearby? If you already compost, partially finished thermophilic makes great bedding for worms. Or save the leaves that you or the neighbors rake up in the fall.

Or you can keep doing what you are doing now and trench compost to feed the worms that already live in your soil.

Thank you sbryce for your response. I'll have to shelve this idea as I cannot look after a worm bin indoors as I am away for various periods in the winter. I had hoped to obtain some worm castings for the containers I do in the summer.

I do have a regular source of horse manure and will use some in trenches for the worms. I know the robins take a lot of worms from my garden so I like to help the worms reproduce as they are my chief source of fertilizer.

The only thing your worms really need in the winter is protection from freezing. You could pile on the horse manure and leave for weeks at a time, and your worms would be fine. If you can protect them from freezing in the winter, you can leave them outside in the winter.

At -35C I don't think it's feasible to keep a worm container from freezing outdoors. Just the reality of zone 3.

I know the garden worms survive as I've seen their tunnels a couple feet down in the hardpan. Come spring they are multiplying like crazy under stepping stones. I guess I'll just keep feeding worms *in* my garden rather than in a container.

Expert? hmmm-www.vermistabilization.com
I guess I could be with time. Bathtub is great, however you will have to make sure that your soil is not compacted and it's going to be hard to get the vermicasts except from the top of the bathtub, which isn't the best way as you'll have to take off the top worms, cocoons, and castings. As you seperate the worms from the castings by screening them through 1/4" screen, some worms and cocoons will get in with the castings; which isn't bad if applying this to the garden. Some castings on top that remain in the bathtub will be disturbed and may cause a certain amount of toxins normally captured by a membrane around the castings to enter the worms habitat. That's why it is best if the castings go to the bottom of the container and then pass through a screen to the floor below. Bedding should be aerated, like mulch, decaying or wet leaves, wet shredded cardboard, etc. The worms in garden appear to be nightcrawlers or large garden worms. The redworm, tiger worm, red wriggler is the ideal worm due to its eating and procreation abilities, plus its a top feeder so you can layer your waste and once eaten the vermicastings are on bottom levels. Don't recommend putting worms in uncovered garden and doing composting there as no decaying material and if uncovered easy prey for rodents. (For others info) RedWorms can be purchased online for around $15-20 per pound. Hope it helps.