On 5/7/11 3:59 PM, Chris wrote:

Let's assume that visible light is the primary source of heat (it's
not, but let us let you play the fool). Western Oregon- where I lived
for years- receives almost no direct sunlight from September to May.
Kind of makes your whole point moot, no? Well, yes.

Now the real fact is that the main heat from the sun is in the form of
IR radiation (ask any photographer!) and IR is blocked by clouds, so
you wind up with a greenhouse that is not much warmer than outside
temps.

This is not rocket science. It is NOT visible light that warms a
greenhouse. It is IR. The covering of the greenhouse has little to do
with it, since neither glass not plastic blocks IR. If you have
constant cloud cover, you have little IR, thus little heating. Sure,
you get a little- but not a lot.

Even you should be able to get it.


Some greenhouses have heaters.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening diary at http://www.rossde.com/garden/diary