Just in case people are similar to what I was a year ago, a cold frame (to me) is a box with a transparent lid and no bottom, which one can set onto the ground. It is a short greenhouse, sort of.
I am committed to building 4 cold frames (of the Fine Gardening design), which is nominally 3x6 (or 18 square feet). Or rather, I can't afford to put acrylic or polycarbonate "glazing" in the top, so I will be using 6 mil PE (polyethylene). I might be able to figure out double or triple PE glazing if I need to.
That design, uses 2x6 wood. I am only planning to make the bottom 2x6 out of western red cedar. The Fine Gardening design has a second full 2x6 stacked on top, and then a half layer (wedge) onto which the top is mounted.
My initial needs, are for trying to grow trees from seed. Once I have enough trees, I could use them for other things.
Most trees grown from seed don't get very tall, very fast. So, a box which is nominally 11 inches tall (2 times 5.5 inches) is probably fine. If you put 3 inches of soil in the bottom, you have 8 inches for the seedlings to grow to before they run into the glazing. I am guessing a person should go "heavy" on the sand fraction of the soil, so that it is easier to separate the soil from the roots come time to transplant them?
But, if at some point I don't need to grow trees; starting vegetables (and other non-trees) might be useful. Or even just leaving the vegetables in the cold frame for the season (as a shorter alternative to a hoop house)? How tall does a person want the cold frame (minus the wedge layer)?
I will guess that if the object is growing trees from seed, a person starts by putting many layers of newspaper on the ground, and then plopping the cold frame onto the newspaper (after the ground has been levelled). Or, maybe that gets rephrased to, if you are growing trees from seed on an ancient fescue pasture, ....?
If after N years of growing trees, you decide to move to vegetables, I think what a person might want to start with is potatoes. I have always heard they were a good preparation crop. If the newspaper hasn't disintegrated by then, maybe fork the bottom a bit, so that the potato plants can get to "the real soil". And after some undetermined number of years, the potatoes may have broken up the top enough, to start planting other things? But, could a person plant tillage radish (aka daikon radish) or one of the big turnips, or ... to now get 1 to 2 feet of the underlying soil broken up enough that lesser crops (like carrots?) could grow there?
I have tillage radish seed. I have yet to actually get tillage radish to do anything useful. Soaking the seed overnight before placing it on the ground does seem to help. But, if you have too high a seed density on the ground, it doesn't seem to grow.
A common building method for rectangular things like these cold frames, is to use a 2x2 in the corners to help tie the corners together.
With most finished lumber (which includes western red cedar for me), a 2x2 is actually a 1.5x1.5. And here, you cannot buy a cedar 2x2. Which means you have to make them.
Standard saw blades for power saws, produce a 1/8 inch kerf. So, if you start with a 2x6 (really 1.5x5.5), you lose 1/4 to kerf. So you get 3 boards which are 1.5x1.75. If I was to use my Japanese handsaw to make the rip cuts, I could get corner boards that were 1.81 inches wide. There are some Japanese handsaws which cut significantly smaller kerf than the one I have.
You can make up "new" corners if you increase the height. I would prefer not to.
For this (Fine Gardening) cold frame design where the "top" level is a wedge shape, the hinges for the top go on the thick side of the wedge. I will call the side where the hinges mount, the "back" side.
On the front side, we are working with 2x6 (actually 1.5x5.5), I would cut the corner posts to be 10 inches long (2*5.5 - 1 = 10). If I want to stack layers, the corner boards are 5.5 inches tall (same as the 2x6), , but offset 1 inch. So that 1 inch of the new board "engages" the lower corner.
On the back side, I would look to do the opposite. The corner board protrudes 1 inch above (for all but the top).
As I am hoping to "grow fence posts and outdoor wood" here from black locust and Osage-orange, I may at some point be able to look at extracting compounds from the bark and chips of trees, to use to treat SPF to increase its lifetime. I seen one report that such treatments compare well with poison treated wood.
A footnote to using the extractives from black locust to treat other woods, as opposed to using commercial poison wood. If a vinyard (winery) is not using oak for storing wine, but it is in wood. It seems that the option chosen is to store it in "Acacia" wood. Black locust is robinia psuedoacacia. And somehow people started using black locust barrels for storing wine. Which is at best anecdotal proof of non-toxicity. I have seen nothing similar to that other champion of fence post lifetimes, Osage-orange.
I have 3 small (two 2x6 boards in front) and 1 large (4 2x6 boards in front) cold frames; all 3x6 feet in size. Three have a double 6 mil poly window on top, the other should be done tomorrow A 3/4 inch dead air space isn't much insulation, and this isn't completely dead.
The "window frame" is 1x4 cedar. The corners are held together with 2x2 steel angle braces and 1.5 inch screws. I then tried to drill horizontal holes for 4 inch #10 screws to strengthen and stiffen the corners. I had 2 "blowouts" out of 16, so not too bad with a hand drill.
The 6 mil poly is first stapled across the long direction in the centre, then cross wise in the long direction, and then I do the short direction starting from the centre and working further out. When everything is stapled, I then use a seam sealing tape to do the 4 corners first (both directions), then the long directions, and finish with the short directions.
Tomorrow we are supposed to see 29C, so maybe I should get an internal temperature with the window closed? The structure isn't "sealed" in any respect at this point. It is sealed in terms of rough carpentry, that some sealing could be applied to seal things. I have a tube of butyl cauking for gaps between the 2x6s.
With 6 mil poly almost covering top and bottom of the 1x4 cedar frames, there is little place for water to wet the cedar. So, it should be okay. Only the bottom 2x6 and the 4 corner 2x2s are cedar. Everything else is SPF (here that means spruce).
I have yet to mount the self opening window thingies. I think the thing to do, is to assemble them, but not engage the opening cylinder. Mount these things so that when the window and frame arms are touching, that the window is closed. There were some dumb straps and tiny machine screw things which were meant to be used in a greenhouse type application, but the screws wiggled themselves out just by me going to the store to ask someone a question about them. I am attaching the lower point to the base (1.5 inch wood) with bigger screws, and to the window frame with smaller screws (smaller holes, actually slots).
Prevailing winds are from the west, but I get NW, W, SW, S, SE, E, NE at various times. Strongest is from the west-ish; but I can get strong winds from the east (killed my corn plants last spring). I have no idea how these cold frames with the cedar window and 6 mil poly will work with the wind.
A couple of times I have attempted to move a short Black Locust for use as shade close to a dwelling but failed cuz I didn't get the entire root out of the clay. Have you had success transplanting them?
Sorry, I haven't had to try and work with anything other than trivial sized trees yet. Once upon a time I worked for a landscaping company which had tree spades. But just resting against a tree spade didn't seem to transfer any knowledge.
What are the dimensions of the drip line of this short tree, how tall was the tree?
Was there anything unusual about the location? Perhaps there was a big rock near where the trunk is, which warped how the roots developed?
The Black Locusts I attempted to transplant were between one and two feet tall. I have successfully transplanted peach trees that I started from seed and left in the seed bed for two growing seasons (We have wild ones that can bear their first fruit in as little time as their third year) but the Black Locust has so far resisted my attempts and so I was wondering if you were going to start the Locust seeds in pots in the cold frame to make the transplanting easier.