Cold climate winter gardening success, failures, and methods

Here in New England, spring is just barely starting, and I've been looking out at our barren garden (well, except for the sage that overwintered).  My hope last year had been to put in cold frames, but the jury-rigged low tunnels I managed to put up instead (too late, and with greens planted too late to mature before winter hit) got crushed by snow and then overheated during the wild swings in temperature that we had.  I still want to do cold frames for the following winter since we have a long winter here, but I need to plan it better this time!

For those of you in similar climates (say zone 6 and below), did you manage to do any season extension or find any crops that could survive and be harvested during the winter?  What worked and what didn't work?

In Iceland, where I permacultured for 5 years, nothing would usually survive in green form over the extreme long winter. Other than "red siberian" kale, and only in some winters.

Some roots were able to overwinter the repeated freezes and thaws, like black salsify, skirret and groundnut (apios americana). Ocasionally a couple of turnips and swedes.
Chives and good king henry were perennial greens but died to the ground overwinter. Rhubarb was the hardiest, surviving right up until near the edge of the ice caps (but still died to the roots).

And I noticed that even nearly all native plants, this far north, either die to the ground, or lose their leaves. Except for juniperus, creeping thyme, a few sedum secies, and native blueberries. The winter is too extreme in Iceland, variable between thick snow covers which turn into ice, thaw, and then form again, many times over the course of a 8 month long winter, that has regular hurricane-force freezing winds.

Another notable exception was dandelion (some overwintered in green form), so providing the only edible perennial green harvestable over the winter.

Have you read Eliot Coleman's books? They are packed with details about exactly this, and I keep coming back to them and rereading parts:
The Winter Harvest Handbook, 2009, has lots of gorgeous color photos and some updated information, tools and techniques. It seems more aimed at the vegetable farmer.
Four Season Harvest, 1999, has more good reading from beginning to end, and feels more aimed at the home gardener in my opinion.
They are both about harvesting vegetables year-round in Maine, in a heavy snow climate. There are many different designs and ideas for cold frames, greenhouses, movable structures, how to avoid snow collapse, etc. Plenty of things can be harvested in mid-winter from cold frames, and these books are full of suggestions. The 2009 book has lots of inspiring photos of greens peeping out of a cold frame or greenhouse in a snowy landscape, and the 1999 book has lots of drawings and diagrams like that. .

Of course you already know that snow is more of an issue than you reckoned with earlier. So I suspect you'd do better with cold frames with rigid glazing. They either have to be strong enough to hold a full depth of snow, whatever is the most you expect in your region, or they have to be steep enough to shed the snow, and tall enough for the shed snow to pile up on the side.

I think the 1999 book has more detailed instructions about making cold frames, with advice I wouldn't have thought of, like having no frame jutting up from the lower edge of the glazing, so snow can slide off easily. You might find discarded glazing to use for your cold-frames, such as windows or sliding doors, or a shower door from a bathroom remodel.

I can extend my seasons on both ends by a few weeks using tunnels, row cover or raised beds, but our winters are just too long and too cold to overwinter veggies.  I wish, but without supplemental heat and light there is no way.  At least not here.  Good luck with trying in your climate.

I have a couple of Eliot Coleman's books, and while I think they are great, I haven't put in the time and effort to really try them yet.  I am doing as Walt said at this point, and just being content with extending seasons.  With a month to two months added to either end of the growing season, I can make a substantial difference in the amount of food I can grow.  As soon as I can get a real greenhouse going rather than my hoop houses, I'm hoping to extend the season even further.

Paulo, I spent a year in Iceland, and I'll tell you, I think the winters are worse here in Wisconsin  The notable exception being the complete lack of daylight for part of the winter.  That is truly a tough climate for a gardener.  A really beautiful place though, I loved the year I spent there.

Hi Im trying a winter garden out this year. im in maybe zone six or seven, im not sure exactly but to make my winter garden i built a decent sized suntrap and then built some slightly raised beds. the beds are just high enough to hold an inch or so of soil and three inches of mulch. everything is mulched the beds are covered from now ish till its above 10 degree c overnight and i have buried pots and flowerpots that hold water as a thermal mass in the beds here and there. the sun trap is only open to the south its blocked from the other sides to stop winds and for the walls to retain the heat. along the walls are plants that don´t need cold protection but are a bit helped by the walls. im hoping that by dividing the area in the gardens by thick hedges and walls  and water. that the little rooms wild be milder microclimates. the specific plants i have are kale garlic pakchoi, spinach, black root (salsify?) parsley and lettuce. il post again here in spring with results. im hoping that the ground at least doesn´t freeze. with a minus 20 c risk in jan/feb i don´t think everything will live though the harsh weather is usually short lived i think without cover the greens would live till around christmas here.