In southern Canada, it is possible to grow food indoors in the winter without artificial light. The amount of natural light the plants receive will be your limiting factor. How well it works will depend on several things:
1) The exact time of year. It’s generally not worth planting indoor veggies in Nov.-Dec. because the days are so short they won’t grow properly. You are better off planting in Aug-mid. Oct. or late January onwards.
1) Your latitude. The closer the poles you are, the shorter the day length and the less intense the sun’s rays. With too little light, your veggies will either long and leggy or will sit there and refuse to grow at all.
2) The type of vegetables you are growing. Sprouts are a special case that isn’t restricted by light. Of normal plants, greens need less light than root vegetables, which in turn need less light than fruiting veggies like tomatoes.
3) Weather during the winter. Sunny weather means more intense light and better growth than clouds and rain. Snow reflects light, increasing that available to your veggies.
5) A reflector. Some cardboard placed behind your plants and covered in tinfoil or painted white will increase the amount of light available to your plants. I’ve tested the tinfoil method against a control and baby salad greens grew noticeably better with the reflector than without it.
6) Size of your window. The bigger the window, the more light it will let in.
7) Which way does the window face: North, South, East or West? You’ll get the best growth in a south-facing window. A north-facing one probably isn’t worth bothering with unless you add supplementary artificial light.
Sprouts are the easiest, fastest vegetables to grow. If you can’t keep houseplants alive and kill anything green, you can still have wonderful success with sprouts.
Moving Outdoor Veggies Indoors
In addition to growing plants exclusively indoors, you can also extend the season for some vegetables by moving them indoors when the weather gets cold. This works well with tomatoes, which are actually perennials when kept warm enough. I find I can reliably get cherry tomatoes into December if I grow them indoors. In one case I even got a few in February. I’m intending to try the same thing with peppers this year, but am not sure what results I’ll get.