Unless your coldframe system is really well sealed with no possible drafts, it will not generate or retain much winter heat. Old-style coldframes had thick wooden sides and actual glass lids. They are also very shallow and can trap a warm layer of air. Your A-frame may have some warmer air near the peak. Low hoops might be better. Or a low-angle A-frame using sheets of twin-wall polycarbonate.

The sun angle is too low now until March to make a grounded milk jug full of water an effective heat source. You could try painting one milk jug to test any solar effects. If your rows are east-west and the soil is sloped to face south, that would help a little.

The freezing milk jug would render winter vegetable gardening a moot point.

Friend that has done this for years uses low frames built over raised beds in a small fenced entryway site with the house immediately to the north. No part of the plot is open to the wind, other than that which comes over the house or fencing. There is no shade from trees, except for maybe the shadow of a western white pine (some distance across the street and down a ways) becoming long in winter.

I basically have a double layer of plastic, one is 6 mil and one is 3 mil. The ends of the plastic touch the ground where I have placed bricks around the whole thing with about 6 inch gaps between each brick. Does this sound like it is sealed well enough or would the 6 inch gaps between each brick allow the possibility of drafts? I will look into making a shorter a-frame because it stands about 24 inches above the box at the moment.

Next year if I tried the manure hotbed technique or got some heating cables would it be possible to have things growing in the middle of the winter with natural sunlight or is there just not enough light in the winter for things to grow?

You have gone to a fair effort to seal the plastic. Just toss some wet leaves around the edges to complete the seal.
Of course having total lack of air movement can create other problems.

bboy has just given an example of a system where winter light has proven sufficient, and you are probably at a lower latitude with slightly more day length and sun.

Get two thermometers and place one well inside and one outside the frame to see how effective your setup is.

Unless the two layers of plastic are separated by an air gap, they are merely the insulating equivalent of a 9mil sheet.

Thanks for all the help. I suppose I just have to try my best with it and be prepared for the possibility of it not growing much until the spring. I will likely be purchasing my first home in the next few years so at that point I will definitely be looking for a place with a clear south facing view and wall space outside the house which a coldframe can rest against. At that point I will likely cover the house wall side of the frame with reflective material to gather more light. I will also probably invest in higher quality materials as well such as plexiglass and I may even install heating cables....someday I will be able to continue gardening successfully into the winter!

Twin-wall poly is used in outdoor setups more often that sheet Plexiglas. My south-facing poly is only slightly fogged after 15 years outdoors. Cuts easily. Slightly lighter than 1/8" Plexiglas.

Up here cole crops like cabbage are grown commercially through the winter in open fields, I think mostly for seed. I see these plantings near salt water, and believe that some years there may be failures due to temperatures below, say, 10 degrees F.

The key to garden during winter is to get crops mature enough to hold & use the garden as your refrigerator storing until you want to eat as well as figure out a way to reduce the rain pelting upon them.

We pick the hardy greens (parsley, swiss chard, kale, arugula, corn salad, broccoli & sometimes spinach) all winter long. I let them all reseed except for broccoli. Freezing weather sets them back some, but we just go out & pick what has frozen then cook right away. Broccoli side shoots keep on producing during milder weather and as long as the stalk is alive will sprout anew in spring. Everything looks pretty ragged by March, but the kale still grows.

Several carpets of kale, lettuce, radish, and parsley have sprouted in different areas after the rains returned. If they don't mature we'll just eat them as microgreens. Onion sets planted now produce green onions. We usually harvest the last of the potatoes & root vegetables by Thanksgiving.

However, you can protect the beds from excessive rain helps a lot, too! I've used upturned clear totes (cheapies that have cracked from years of storage use) with stakes on corners to prevent wind damage and have one side a bit higher to let air inside. It's easy to remove stakes from one side & harvest. This year's mature kale, broccoli, & cabbage don't fit inside the totes, but I have hoops up ready for plastic covering hopefully by the weekend. I have used fabric row covers on cold nights in the past & it helps. Both purchased row cover or translucent window sheers or shower curtains work great! When our son was young he asked why I had decorated the garden with butterfly fabric when it was winter and no butterflies out there. I still use those some shower curtains, but my purchased row cover has tears in it after covering some of our tomato plants this fall.

Hope that helps, Corrine

Here is a link that might be useful: Read Linda Wilkeson's past articles on winter gardening

I've used this resource for our fall & winter gardening. The trick is to reserve garden space for planting mid-late summer and early fall. Linda Wilkenson's book has good diagrams and explanations of succession planting and interplanting short with long season crops to help you figure out your space.

The resource below also has planting dates to help you plan ahead for next year.

Here is a link that might be useful: Fall & Winter Gardening in PNW

I also highly recommend the book Winter Harvest Handbook by Eliot Coleman. He also has some great videos on Youtube. In his book, he mentions that vegetables grow really slowly from Nov 7th to Feb 8th in the NE. The key as corrine1 mentioned is to have mature enough crops by the time winter hits.

I like to have things growing during the winter too and as someone else already mentioned some things can just live outside. I don't harvest all my Broccoli, Kale, Chards, Mustard, beets, carrots, collard greens or parsley. I harvest all winter long with no problems.

Add to BIblegeek's list garlic, cabbage, long season radishes, turnips, cilantro. Most of these will survive down to 20F.But if you want to grow thing from squashes, pepperes... you will nedd a fullfledge heated greenhouse. ,

I've experimented with growing things in the winter, but the biggest problem is lack of daylight. Even if every day would be sunny, the days are too short and the light not intense enough. And those of us who live up here (in Bellingham, about 15 or 20 miles south of the BC border) know that it's usually cloudy with a chance of being wet. My house plants even get depressed. The best I did was turnips and kale, and those really didn't grow during the winter months, so much as they did not die.

Probably the best is to get a late summer crop going and allow it to remain all winter. I've harvested carrots and onions well into December with no problems as long as they were started early enough.