"Rick" wrote in message
...
On Mon, 02 Aug 2004 15:07:03 -0400, dps
wrote:

chaz wrote:
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.

chaz






Things to consider:

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.

I built this one and have been enjoying it for the last 4 years.


http://www.bae.ncsu.edu/programs/ext...greenhouse.pdf

-Rick

Rick,
How do you handle heating, ventilation, etc? Where can I buy plastic for
this project?

"chaz" wrote in message ink.net...

Rick,
How do you handle heating, ventilation, etc? Where can I buy plastic for
this project?

I am not rick, but here is what I have to say:

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.