In article ,
Jeff Thies wrote:

Billy wrote:
In article ,
Jeff Thies wrote:

Bill who putters wrote:
In article ,
General Schvantzkoph wrote:

On Sun, 07 Mar 2010 12:36:25 -0700, Suzanne D. wrote:

"General Schvantzkoph" wrote in message
...
I'm thinking about getting a greenhouse this year to extend my season
(I live in Massachusetts). Last fall someone on this group suggested I
try a popup greenhouse because they are very cheap (under $150, some
as
low as $50), rather then make any kind of major investment. Does any
one have any experience with them?
I bought a $110 plastic greenhouse from Walmart. It was easy to
assemble. The workmanship was a little shoddy, but nothing
drastic--just
a zipper off-kilter, some crooked seams, that sort of thing.

There were two problems I saw, and these might not be problems for you:

1. It didn't stay warm at night. I'd see seedlings popping up during
the day (when it was VERY hot inside the greenhouse), then they'd die
overnight. If you are going to put some nighttime heating in it, then
this probably wouldn't be an issue for you.

2. The wind completely took it away. We staked it down all around AND
put concrete cinderblocks around the perimeter of the greenhouse, but
on
one windy night the entire thing was pulled up from its stakes and
blown
into a tree, where it twisted and broke. The plastic was ripped, and
the metal bars were bent and sheared clean off at some places. (A few
of the stakes were still in the ground; the wind had separated the
poles
at the joints and lifted them away!) If you do not have a lot of wind
where you live, this shouldn't be a problem.

I really like the idea of these inexpensive greenhouses, but for me it
was a waste of money.
--S.
Thanks for your feedback. Both of those things are issues, I wondered
how
something that was basically a tent could stand up to any kind of wind,
apparently they can't.
Maybe nestled up to a south facing wall with east and west protected
with a few cider blocks.

I like that idea.

You may wish to look at home made hoop greenhouses. Easiest way is to
drive rebar into the ground, and pop the hoops on the exposed rebar. You
will need to recover every few years, but the material is cheap.

One example:

http://westsidegardener.com/howto/hoophouse.html

My general advice, curves are strong and resist wind. If you can prop
this against a south facing wall you will cut your heating needs.
Greenhouses lose heat at night, and lots of it. Without added heat,
inside temperature will be the outside temp by morning if not long before.

I'd investigate composting manure for heating. Not very esthetic, but
practical.

Before I started to garden, I found the smell of manure very offensive.
Now when I smell manure, I think of gardening.

Perhaps perhaps run pex through the remotely located compost pile and
pump the heat into the greenhouse when needed. Lot's of options.

As I understand it auto venting device is
really of import or the heat which varies a lot due to no solar mass
fries or freezes your plants. I's add gallons of water maybe half your
space to try to moderate the temperature swings.

Water is one BTU per pound water degree F. Heat loss for single layer is
~ 1 BTU/hr per square foot times the temperature difference. It adds up
to a lot of water as Bill has said. Try Drums. Other materials store
heat, but not as well as water.

Double or triple wall polycarbonate will cut the heat loss by almost a
half to two thirds.
and reduce light by 20% - 30%, respectivly. Six mil polyvinyl will
reduce light by 5 - 15%. In low light situations, this could be
important. I was planing on a hoop house, but decided that I couldn't
afford the light loss in my particular situation.

It's always a tradeoff. You could have removable insulation and put it
in at night. But that can be a hassle. I've done some removable with
reflective bubble wrap such as this:

http://www.radiantguard.com/reflective-insulation.aspx

I also have this on the north wall and it reflects light in rather
than letting it escapes. It can also be pulled over the top, instead
of inside.

I've got some folding multilayer 1 mil mylar "storms" that has very
low light loss, but it has it's issues.

My benefit here is that while I have very little sun during the
summer, falling leaves changes all that. I may have to become a winter
gardener...

At any rate, there is a lot to consider. And I'm afraid more that the
casual greenhouse user would like to consider!

As you have said, anyone can grow in ideal conditions, it takes a
gardener to grow in what is available!

Jeff

I'll retrofit my solar cabana with mylar storms this fall. Clear
mylar degrades in UV so it needs a UV outer barrier.

I've been using vinyl shower curtain liners. They are very clear and
hold up well, so far.

Jeff

Small maybe beautiful
but one has to work harder on your design.

--
- Billy
"Fascism should more properly be called corporatism because it is the
merger of state and corporate power." - Benito Mussolini.
http://www.youtube.com/watch?v=Arn3lF5XSUg
http://www.thirdworldtraveler.com/Zinn/HZinn_page.html