Cold Frames

Coldframe Notes from the Trenches
I have found that polycarbonate plastic corrugated sheets, (Lexan) while initially expensive, save in the long run.  I tried a few sizes of boxes, mostly based on the scraps of wood I had, and found that a box that fits some multiple of the plastic trays (i seem to inevitably use these as they fit the mix of bought starts and leftover trays) are the least frustrating, and block the weeds that would want to grow around the edges.

So one of these strong and light 8 foot sheets, cut into fourths, can cover a certain number of 10x20 trays.  There is a drip overhang, the wood dimension, the pitch (the long side of the triangle) and a bit of fuss room for the tray edges.  I think it works for 8 trays, arrayed  2x4 or 1x8, or combination there of.  As the plants grow, it seems necessary to move them around.

That said, we might build a small box to fit a single sash a la ReCover, or something else.  After a season with old $5 sashes, the putty and lead paint, insulted by their new angle, begin to fertilize the soil.  I had two big sliding door blanks, double glazed. Lifting these every day was so frustrating I must have dropped it too hard, for I remember what happened next: picking up diamond sized pieces of tempered glass for hours and hours, while Jasper drove his trucks in the mud.  Interestingly, tempered glass lets ultraviolet light pass, so there might be an advantage.

The Center has a big stash of 1x pine, and you have greenhouse plastic.  That might make a good interim, and you could add more permanent solutions as productivity soars.  My friend Harald made these large, 4x8 perhaps, and just flipped them over each morning for access.  In California, you don't really need to worry about snow load!

As for wood, plain 2x lasts a long time.  I put boiled linseed oil on the wood when I first made the last batch. I cut rot off the bottom of 2x10's after some years, and bought more time.  Now I have pressure treated bases, and fir or pine atop that.  Critters seem deterred if the base is buried a bit, and frozen in the ground.  If the roof needs much pitch, the two or three rows of wood can be staggered for strength.  Cut a diagonal and the board is flipped for left and right sides.  I had low pitched ones, say 6" higher in the back for years.  Last spring, I made new boxes closer to 45 degrees to match the latitude here, and maximize the sun in the winter.  Not sure if these are any better yet.  Still had snow to remove.  Another thing to try: Longwind Tomato Farm found that painting every surface white in the greenhouses increased productivity and available light.  It was only a tiny percent, but it adds up when you are accounting for literally millions of dollars worth of tomatoes.  And white paint is very reflective, over 30% more than aluminum foil.

Spinach this year seems to have not gotten enough water.... Not sure how to remedy that one.  We had lots of cold dry.  Have to be on top of that one.  Might be due to the new pitch letting in more sun?

G