DIY Greenhouse

This year I am tackling the process of figuring out how greenhouses work. 2 winters ago I simply put plastic sheeting over G1 (Garden 1) in an attempt to frost/freeze protect some of my vegetables. I, still being a near-complete novice and still having a black-ish thumb, thought that this would be totally sufficient. I put a remote thermometer on the inside, beneath the plastic, and one on the outside near the garden so I could monitor the difference between my makeshift greenhouse and the outside temp.

What happened shocked me. I eagerly watched the temps as the sun started to fall behind the horizon and at first everything looked good. The temp in the “greenhouse” was warmer than the outside temp. Check! However… as the hours went on, the temps not only equalized, but the temp in the “greenhouse” actually got colder than the outside temp! Something must be wrong. Did I swap the thermometers? Nope. Is the bed losing heat due to the sides being made of metal? Perhaps? The following day at around 10am I noticed my little greenhouse got HOT. I don’t remember the temp but it was easily over 100 under the plastic and below freezing outside so I opened it a crack and the heat quickly started pouring out! OK. This is a bit more complicated than just draping some plastic over the bed! 😅😳😭 I did some research, as apparently I should have done beforehand, and found out that greenhouses do indeed get colder at night. I recently found a saying on a gardening forum or facebook group which goes something like “twice as cold at night, twice as hot during the day.” That obviously isn’t 100% accurate but it gets the point across. I won’t go into the scientific reasons for all of this (the obvious greenhouse effect during the day kind of speaks for itself). But now having experienced these forces in effect, along with having read the scientific reasoning behind it all, I knew I wasn’t quite prepared for this challenge yet. I wouldn’t mess with trying a greenhouse until I’ve had time to do some thorough research, and am prepared to do it right.

Fast forward to this year. I’d now done a fair amount of online research, watched youtube/rumble videos, read stories and advice from gardening sites, etc. It’s time. Time to test build a proper hoophouse/greenhouse. My goal was to build one large enough that it would be a great -to scale representation- of one I would like to have for the business. A test of what problems I will encounter and have to solve that go along with the entire process i.e. – building, wrapping, heating, venting, unknown, ignorance, and so on. If something major fails, (which I was/am hoping I can keep on top of before it kills everything in the greenhouse) then at least it’s not as large of a learning loss as something massive like the roughly 70’ x 20’ I would like to build.

I decided this one would be 10’ x 16’. This seemed like a great test size and worked with the location and materials I had on hand and planned on using.
Location: It’s right in front of my house, facing south, next to my pergola. This will give it the sun it needs, and my house should block the majority of northern winds. Having it next to my pergola will put it right where I hang out, and I can easily keep an eye on it and my mind on it during this whole process.
Materials: I had metal fence posts I brought with me from my old residence and I figured I could use them for this. I wanted it sturdy, as we get some pretty windy days, but as cheap as I could. I didn’t want to make it with much wood touching the ground for fear of termite/ant luring near my house.

I made the hoops, the curved roof pieces, out of 1/2” metal conduit and a conduit bender. I screwed them into the posts with metal screws and conduit brackets. I rubber paint coated the bottom wood 2×4’s and stained the others. The windows I made from 1’x2’s and left over plastic from the 250 gal tote I cut in half when I made my duck pool earlier this year. I’ll have to do a post on that later. I really don’t feel like going into everything/all the rest right now as my fingers are getting tired of typing and so am I, so I’m just going to post pics/vids and possibly come back to this later… heh.

Problems I have encountered and tackled so far:

1st problem: Wind. The wind, even on not that windy of days, demonstrated that 1/2” conduit for the roll up sides is not weighty enough. The wind lifts these up fairly easily. I currently resolved this by putting a 16’ length of toprail snugged atop the conduit piece while it is rolled down. When I am done for the season with the greenhouse plastic I will likely re-do it and attach it to the toprail instead.

2nd problem: Gap leakage. I knew there would be some leakage at the bottom between the roll down plastic/conduit tube and the wood along the ground but wasn’t exactly sure what I was going to do about it. I ended up just shoving pieces of fun noodle between the ground and the wood where there were gaps, and then slicing fun noodle long ways in half, and stapling them to the 2×4 along the ground. This seems to give it a nice near-air-tight seal when the polled plastic is resting atop it.

3rd problem: Venting enough heat. I discovered this extremely quickly as I vastly underestimated the greenhouse effect of that much area. I initially bought two small fans I planned to use to vent the uppermost part of the greenhouse (heat rises). The amount of heat the greenhouse captures is insane! I didn’t even try to put these in the greenhouse. They would do almost NOTHING compared to how much needs to be vented. I ended up putting my large “room mover” fan in there and with it on high during the day, pointed almost straight up, it is able to keep it around 90 degrees with both vent windows open, and sometimes I have to leave the greenhouse door open. Yes, I do have my roll up sides but to reduce wear and tear I’d like to refrain from undoing/redoing the wiggle wire daily if possible. I will likely need to roll those up during those intermittent, but inevitable, 80-90 degree days we’ll get mid-winter and before our last frost date.

For heating during the night, so far a 1500watt infrared heater with my big fan on low has been sufficient enough to keep it about 10-15 degrees warmer than the outside temp. For now, I am using an extension cord, but I did make sure to get a 10 gauge cable. For colder days, I have purchased a propane powered Mr. Heater to supplement (I still need to figure out how to use it) the electric heater if it gets too cold AND/OR when the power goes out. I have lived here going on 3 years now and the last 2 winters we lost all power between 1-3 days. I do not want ALL of this effort to be moot due to losing the power on my greenhouse heater. The reason I am using the electric one as primary is because cost-wise it is cheaper due to me having an electric credit from all the solar I generate during the year.

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