I am considering making a small greenhouse, before I actually make the plunge into something legit. I can buy a greenhouse locally for about
1100.00 which would be an 8x10 portable unit. Its like a storage building, but with translucent fiberglass panels, no floor, and windows for ventalation. I am looking at making a 10'x10' x 3' tall stucture from PVC and clear plastic. I know its not a greenhouse, maybe a souped up cold frame, but it would be cheap. I thought I could string up some lights (4?) to keep the temps out of the freezing range? I have some lemon trees I want to grow over the winter and there are too many to bring in doors.
I would love you guys to shoot holes in this idea. I have ZERO experience with a greenhouse.
The clear plastic you buy in the hardware store is not generally UV resistant, and will start cracking in one to two months of exposure. Make sure you buy the UV stabilized stuff. 6 mil is common. Look for it in greenhouse supply houses.
The PVC frame has to be strong enough to withstand wind and snow(?) loads when the plastic is on it. You don't want a flat roof. You need enough slope so rain will not form puddles in the plastic. Rain is really heavy when it collects in a dip in the plastic, and can rip through.
3' high is rather cramped when you're trying to work inside (maintaining your lemon trees as necessary, or just planting them). Making it 5' high wouldn't take significantly more framing or plastic.
Ventilation is NECESSARY. Preferably automatic. On a sunny day, the temperature can get over 130F, even with 30F outside. You want it automatic so you can go to work and not have to worry about the sun coming out in the afternoon. There are automated cold frame devices that would probably work.
If you want to keep it from freezing, a lot of water containers will help (assuming you're in a temperate region where lemon trees grow). Water will release heat as it freezes, keeping the temperature at 32F until it's all frozen. If the temperature gets below freezing for several days at a time, this won't work well. I find a cheap space heater (set on concrete blocks) will keep a fairly large space above freezing in New England in the spring (not the winter). Lights running all night might be an annoyance to your neighbors. The space heater is not quite so visible.
google "advice sought on hoophouse" in rec.gardens.edible. There was a post by Bill Bolle in that thread that pointed me to how to make a large and cheap hoophouse. I now have two of them (just built them),
26X13 each. I also have permanent PVC structures over three of my beds (approximately 25X4) to overwinter vegetables (I pick them in January, in Michigan, and overwintering lettuce is ready in April). One plastic layer gives you 15F, so if you are within 1.5 zones of lemon growing, you should be OK.
live in Texas with the sun beating down, very high winds in winter and spring, and mine is about 4 years old. I put it up in the fall and take it down in spring and it takes about an hour or so once you get the hang of it. It's got galvanized pipe, at least the one I bought. There is not top ventilation, but adequate door opening and three windows with mesh to keep insects and birds out. For the winter, I put a tarp down and attach it to the bottom so air cannot enter through the bottom. I use a small electric heater on nights which go down into the late 20s and it's enough to keep frost out of there. Keep in mind, I live in USDA Zone 8b, and while we can get temps in the teens and lower, it's very rare. If you live up north, this will not be a very efficient greenhouse.
BTW, I also grow lemons and winter them in this greenhouse.
1) I buy the clear plastic at the store. Yes, it is not UV resistant. You will have no UV damage until late in the season. I usually uncover my beds on April 1 and store the plastics in the dark. Plastic lasts two years at least and is usually done in by pulling it while it is covered with ice (it breaks). One roll of 4mil clear poly, from the Home Depot paint Dept, is some $25. Plastics never broke under heavy snow, though it did form puddles. Also the PVC hoops are quite flimsy. I bought clamps for plastic at Territorial Seeds.
2) don't ignore irrigation. my tunnels are over a depression in my yard, where runoff water collects, and so even though I don't water in the winter, they get plenty moisture a few inches below the surface. But the first few inches of bed soil are Sahara dry by January.
3) the soil provides enough heating and cooling, at least for low plants like salad greens, as long as mulch is removed so that there is good thermal contact. I never had a problem with kale or collard either. Otherwise, the standard way to cool/heat a greenhouse is to cover the North wall with 55 gallon drums filled with water. Each has a thermal capacity of 40 MegaJoules, which sounds like a lot but it is not. This is a little project in itself, as you probably have to stack them two high and secure them with chains to sturdy posts to avoid them falling and killing people.
4) ventilation for cooling is needed only in some cases (not for my tunnels, though it will be needed for my greenhouse). The standard way is to have two temperature operated louvres, one at the door, one opposite. They open ad create a draft when the temp exceeds 85F. They are thermal powered. I bought mine at Territorial, but I have not installed them yet. ventilation is also needed for CO2. My soil has enough organic material that CO2 is not a problem. If in doubt, a pile of manure in a corner will provide enough.
Why not just stop spamming this newsgroup. Your rapid-fire multiple promotions of that worhtless ultrasonic device, & your pretences of being a happy customer rather than a commercial spammer, show that you are not to be trusted for ANYthing.
And today's slogan remains: Honest, competent companies do not post spam in newsgroups.
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