Build It Yourself PVC Greenhouse Plans
First thing to understand
This is not a greenhouse to walk inside if you live in an area with snow. Snowloads will collapse this greenhouse in a heartbeat. I know, you've heard to the contrary but having seen metal hoop houses destroyed in a few hours by a dump of heavy snow, I can tell you the practical answer is that this kind of home or backyard greenhouse won't last through a snowy winter unless...
Unless you heat it with enough heat to melt off any snow before it has a chance to build up.
This takes an amazing amount of heat - I would routinely turn up the thermostats into the 80's to ensure enough heat got through the plastic to keep the snow melting off. In the commercial world, this is cheaper than having to replace the plastic, greenhouse or crop. In the hobby world, you'll have to make this decision.
This is the kind of backyard greenhouse that works extremely well as a season extender.
You cover it as soon as the snow leaves in the spring and let it heat up the ground. You use it as frost protection in the early spring removing the plastic during the heat of the summer (or it will produce too much heat and reduce the growth rate of plants). And finally, you put the plastic back on in the early fall when the nights start getting cool. And you grow with this until the snow fall starts coming when you remove the plastic again. (do this on a sunny day when the plastic is warm so it doesn't crack).
So here's how to build one.
Rebar Into Ground
Drive lengths of reinforcing rods (re-bar) every four feet down the length of the greenhouse you want. Leave 12-18 inches above ground and equal distance below ground. Point A on diagram
Make the greenhouse as wide as you want - a four-foot wide cold-frame or season-extending backyard greenhouse will give you the maximum use of space. You can reach into the middle from both sides during the harvest and working season. But you can make them as wide as you want if you want to walk upright inside.
And while the actual distance between stakes isn't shown on the pvc greenhouse plans below, a distance of 3-4 feet is commonly used.
Parallel Second Row
Drive the second line of reinforcing rods parallel to the first so the greenhouse is square.
Lengths of Hoop Pipe
The somewhat "tricky" thing is in cutting the lengths of pvc pipe to fit. Rather than me giving you dimensions for every width in these pvc greenhouse plans, let me suggest you experiment *without* cutting the pipe first. Shove one end onto the protruding length of rebar and then bend the pipe over to the ground at the angle and shape you desire. Given that this is a temporary structure, you'll quickly see what shape you like without having to put a crimp in the pipe. Cut the pvc pipe to this length.
Cut as many pipes into this length as you need - one length of pipe for each stake.
Fit them over the rebar so you have a length of hoops down the pvc greenhouse.
At point A
It is important to have stability in the structure and these pvc greenhouse plans call for you to lay a length of pipe across the top of the hoops and make it continuous all the way down the length of the structure. Different plans call for different ways to hold it here but I prefer to use a duct tape and simply tape it all together. Clamps rub on the plastic and can tear it. Duct tape is smooth and easy to use with no damage to the hoops.
This is point B
Some folks using these pvc greenhouse plans like to add a corner brace but this is unnecessary unless you live in a high wind area that might push the entire structure over. If you've built the structure so that the hoops are higher than three-four feet and then you really do want to add the extra braces to hold it stable in the wind.
Only necessary at the ends at point A1 and C Note that point C is about half way down the arch of plastic. You're looking for lateral support so making it on the sides rather than the top will add strength.
Cross Bracing Plastic
Finally, many gardeners forget that wind can do some pretty interesting things to plastic. If you live in an area with high winds and the pvc greenhouse is exposed to those winds, you might find it very useful to take a length of soft rope and criss-cross it over the top of the plastic to hold it against the pvc pipes.
In high winds, greenhouse shapes sometimes work as air-foils (like plane wings) and tend to lift the plastic right off the frame. Running a criss-cross pattern of rope or twine down the length will reduce this tendency.
The ends of the plastic can be simply looped together, tied with twine and anchored to the ground with heavy weights. You'll be opening these ends up for ventilation so they should be easily moveable.
Holding Down Greenhouse Plastic with PVC Greenhouse Plans
The sides of the plastic should be held down using methods described here.
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