Whilst I grew up in Australia on the East coast, mostly in Sydney and South of Brisbane, my family lives in the Sverdlovsk Oblast, Russia - Latitude 57° N, Köppen Dfb-Dfc. Over the past 20 years I have seen Summers where +30C is common and Winters of -30C are also common. Heavy snow in September, followed by an Indian summer in October, November, is not unheard of.
Normal Summer crops here are potatoes, carrots, cabbages, beetroot, onions, garlic, sunflowers, corn, Brussel sprouts, tomatoes, cucumbers and a wide variety of herbs and berries. Berries and fungi are also foraged. Some crops get an early start through cold frames, tomatoes and cucumbers especially. Watermelons and pumpkins are grown on waste ground. Imported fruits and vegetables are widely available, mostly from the 'Stans, South America or Turkey. I can buy bananas here cheaper than in Australia.
However, in Winter, I cannot get good salad greens easily. Pickled vegetables are readily available and I love them. But man cannot live by bread and pickles alone. Fresh fruit is also expensive, and often of poor quality du to long transport times.
We now grow sprouts and grow greens from vegetable tops on the windowsills. Carrots and beetroot are good for this. I want my grandchildren to have a varied and healthy diet. They "hate" vegetables. Unfortunately for them, I hide vegetables in almost everything I cook. The meatloaf that they love so much, cups of grated vegetables and cooked buckwheat, bound with eggs.
Anyhow, I'd like tis to be a thread about growing food in USDA Zones 1-4. I'd love for this old dog to learn new tricks.
I lived for a number of years in Zone 3. 40 f below was common. I saw 53 below once. Cars were freezing up on the interstate while in motion. I saw snow in June. It was always a challenge to get tomatoes to ripen before the frost. Lots of Epsom salts. Today I would absolutely have a high tunnel ....or several. On the other hand, we had great root crops (very sandy soil).
"Good decisions come from experience. Experience comes from bad decisions." ... Mark Twain
I'm in a similar climate with winters getting a bit colder though. I don't know of anyone who grows or harvests any greens in the depth of winter though.
This is the first year I am using a high tunnel and know the the peppers and tomatoes are loving it. I am planning on planting spinach in it with the goal of stretching the harvest into winter but i am unsure of how well that will work so far.
Elliot Coleman has some books on setting up a large winter green harvesting system in Maine. He's warmer than you but his ideas may be a great place to start.
"Hundreds of years from now it will not matter what my bank account was, the sort of house I lived in or the type of car I drove... But the world may be different because I did something so bafflingly crazy that it becomes a tourist destination"
I lived in zone 3 most of my life, currently in zone 4. Winters are long and boring for food.
I have started to dehydrate a lot of bulky things to use later in soups and stews for winter. I am trying out storage crops like beets, celeriac, onions, maxima squash, carrots, etc. Potatos are surprisingly nutritious, especially with the skin. I can have tomatos until Christmas if I pick the green ones before frost. Greens are in short supply, so also trying to learn to start brassicas indoors and plant peas while the ground is still partially frozen. I am considering chopping basil and oregano and freezing with water in ice cube trays for winter cooking. Sauerkraut is a good winter food too. Pickles are good - I pickle beans, beets, carrots, hot peppers, zucchini, etc, instead of just the common cucumbers.
Hostas and rhubarb are perennials for spring eating, and chives.