The phytochrome, the red-light absorbing photomorphogenic receptor molecule in plants, controls the stem height of the plant growing in a greenhouse scenario. As can be seen from the article, the link to which is included below, the effect is dramatic over the absorption range 300 to 800 nm with maxima in red (600 to 700nm) and far-red (700 to 800nm). This suggests to me that plants still need a fair amount of red light to encourage stem growth. However, by controlling the ratio of red to blue, you have a very sensitive method of controlling the plant height. Here is a link that might be useful: Clemson Spectra Study

I still have to go out and measure it to make sure my memory was correct in 2012. (Laughing at self here.) As you might remember, the greenhouse kit we purchased was actually two 10' x 12' grow houses (no longer sold there so I can't go look up the size) from Gardener's Supply, joined together. So, our confusion stems from whether we put them together with the 10' representing the length or the width of each house, and Tim thinks I describe its size differently every time I say what size it is. I probably do. (Laughing again.) I'm not good at estimating or remembering numbers, and I also think I have the size of shade cloth I ordered swirling around in my brain further confusing the numbers. The reason I currently think that the 10' is the width and the 12' the length of each house is because my potato beds are 12' long. How is this relevant? We tried to build raised beds that ran the length of the greenhouse inside the greenhouse so I could grow plants in there "in the ground" all winter long. We built two along the north wall. After discovering (before the beds were even completely filled and in use) that the cats thought we were building them a really nice cat box/porta-potty in the greenhouse, we ditched that idea quickly and repurposed the wood to build hardware-cloth lined potato beds that would exclude voles in the garden. I remember taking the lumber apart and dragging it down to the garden. I remember moving the amended soil, one wheelbarrow load at a time and discovering it was full of fire ants. I remember the cats being mad and sulking about it for a long time thereafter. They still love the greenhouse for warm kitty cat naps on a winter's day, but they go out into the yard now to use the bathroom since there is no nice raised bed of fluffy soil in the greenhouse any more. I'm pretty sure the two oldest potato beds are 12' long by 4' wide, so that would give us a greenhouse that was 24' long and 10' wide. Hopefully that is correct. If the two oldest wire-lined potato beds built from the repurposed greenhouse lumber are 10' long, I'll revise my answer. This is all so much more complicated than it should be. I must have some form of numbers dyslexia because I never can correctly remember sizes and dimensions. Regardless of all the above and no matter what size my greenhouse is, I need for it to be bigger. To make it bigger, we have to move it, but I'm toying with moving it elsewhere over the summer when it is not in use and making it bigger.

I was all set to remove film when I realized that it would very difficult to reinstall closely trimmed film. So I took used driptape from another tunnel and strung 6 lines above highest perlins, pulling them taught on top of arches. I also placed 2x6" support braces,2 per arch, on alternate arches. The braces are simply temporary boards from ground to arch which I'll remove this Spring. The final step was that I ordered another cover and my intention is to apply a double inflated second layer this spring. All this is assuming that the present film holds up to future snow loads. With the braces I'm confident that the 2 3/8" diameter arches won't cave but film may not take the weight of a heavy snow.

If you have somewhere at the door end to attach a clip-on 15cm fan and cut a 30cm 3-sided flap at the other end it would be functional all year long.