Greenhouse Idea w/ Questions

[microgateway]

So, I was thinking about what I'm going to do next summer with all of my cacti. I could generally keep them outside, but I'd like to protect them from excessive rain and sun. Still, I really don't need any climate control, so I figured I'd just go with the cheap and spacious option, a hoophouse (technically a greenhouse. I have a book on greenhouses from the library that gives a great descriptionfor making a PVC-based 10' x 15' greenhouse. I may scale that down to 10' x 12' or 10' x 9' though. So, here are a few questions and concerns I have. I appreciate you taking the time to read this, I hope you'll chime in if you have any answers.

Where would be the best place to ge the plastic? I kind of want something cheap.

I was thinking about facing the wall south, that way all of the light would be filtered throught the wall and not slip in through the door. Also, the prevailing winds would come through the door, which would serve to help ventilation. Still, that could be a problem during storms by blowing rain in. Thoughts?

What's the maximum length for dormancy? This may pose an issue...

Thanks in advance.

[Andy_CT]

What's the maximum length for dormancy? This may pose an issue...

I would imagine the bigger the cactus the longer it can stay dormant. Mine are dormant October thru mid April so 6.5 months doesn't seem to bother established plants. Keeping them cold enough is key.

[iann]

Have you thought about just having a roof over the growing area? An enclosed greenhouse type structure might extend your growing season a little in spring and autumn, but a small hoop-house won't hold any heat at night.

[lancer99]

a small hoop-house won't hold any heat at night.

Any enclosed structure will hold in heat at night.

-R

[microgateway]

I wasn't planning on using it to extend the season much, just to prevent excessive rain and sun. Did you mean summer nights? I thought desert nights were cold enough that it wouldn't make much of a difference.

So, I think I'm using this for the cover. It'll cost $30 and I'll have some extra.
http://www.acehardware.com/product/inde ... 0570512113

[iann]

Any enclosed structure will hold in heat at night.

Let me clarify. A small uninsulated unheated plastic structure will not provide a minimum temperature usefully higher than the air outside.

Beyond this example, your statement is patently false. The internal temperature of a structure depends on many factors and in some cases it will even be colder than the outside air temperature. The obvious example is a car on a clear night where the upward facing metal and glass surfaces rapidly lose heat by radiative cooling and then quickly cool the interior by conduction through the metal. If you've ever spent a winter night in a car you'll know what I mean I think I've even experienced this with an aluminium and glass greenhouse on some nights but I don't have the equipment to be 100% positive about my temperature measurements.

[microgateway]

Thanks for the in depth response. Well in that case I guess I'll just go with the standard growing season for my area. Since I'm south of Boston and less than a mile from the ocean, it's longer than one would expect for MA.