Year Round Greenhouse, How Practical?

[Jeff]

In a moderate climate (Oregon, about 100 miles from the coast), how practical would it be to try to raise vegetables year-round in a greenhouse?

- Jeff

[David E. Ross]

I know someone who raises herbs commercially year round in greenhouses. I think she has four of them. She sells the fresh herbs at a farmers' market.

Besides providing protection against winter frosts and freezing, a greenhouse protects plants against being beaten down by wind, rain, and hail (except for severe hail, which can break the greenhouse panes).

With screens for the transoms (windows that open), a greenhouse can also protect against many insects, especially grasshoppers. However, that can also prevent the use of bees for pollination.

[Billy]

Do you have full sun all day?

[Chris]

In OREGON???

Heh. I went to Oregon State, in Corvallis. Three of the 4 years I was there, it on September 1st the temperature dropped to 50 degrees and it started to rain. The temp never changed and the rain never stopped until May 1st.

OK, an exaggeration, but not much of one. Now, Corvallis is about 50 miles from the coast, so it sounds like Jeff is somewhere in Cascade Range. You can count on more snow up there than in the Willamette Valley.

Jeff, it really depends exactly where you are. I knew people near Salem who raised fuchsias year-round, and they probably are less hardy than some vegetables. Also, it depends what you want to grow. I'd give up on melons and cucumbers, but lettuce, broccoli, cauliflower, peas might all do well.

Chris

[Billy]

Some of my worst sunburns came on overcast days. Melons and corn may not grow in a green house during his winter, but with nothing physical blocking his sunlight, he should be able to grow lettuce, kale, chard, broccoli, cauliflower, and maybe even peas.

"Gardening adds years to your life and life to your years." - Anon

[Chris]

Sure- same here. But sunburn comes from ultraviolet radiation, and that doesn't add too much in the way of heat.

Indeed.

[Billy]

???? It's a greenhouse! Greenhouses have an effect. True the interior temp will be proportional to the exterior temp, but the greenhouse will be warmer.

[Chris]

My point was that UV radiation pierces cloud cover, but infrared does not. UV does not make you warm. That's why it's easy to get a sunburn on a cloudy day- you never feel your skin warming up. IR is what heats up a greenhouse. And I think you underestimate the very, very few sunny days western Oregon experiences through the winter. And if Jeff is indeed in the foothills of the Cascades, he's going to have _much_ colder weather there than what I had in Corvallis.

"Last year, 43 people fell off their bicycles in Corvallis- and drowned." (Popular t-shirt at OSU)

Chris

[Billy]

A greenhouse is a structure with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible solar radiation (for which the glass is transparent) from the sun is absorbed by plants, soil, and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. In addition, the warmed structures and plants inside the greenhouse re-radiate some of their thermal energy in the infra-red, to which glass is partly opaque, so some of this energy is also trapped inside the glasshouse. However, this latter process is a minor player compared with the former (convective) process. Thus, the primary heating mechanism of a greenhouse is convection. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. This principle is the basis of the autovent automatic cooling system. Thus, the glass used for a greenhouse works as a barrier to air flow, and its effect is to trap energy within the greenhouse. The air that is warmed near the ground is prevented from rising indefinitely and flowing away.

Although there is some heat loss due to thermal conduction through the glass and other building materials, there is a net increase in energy (and therefore temperature) inside the greenhouse.

[Chris]

Please read for comprehension.

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.

Chris

PS: When you copy and paste as you did from Wikipedia

should provide references. Otherwise it is out and out plagiarism. Not to mention that Wikipedia is not the best source for information.

[David E. Ross]

Some greenhouses have heaters.

[Billy]

I have no interest in taking your part ;O) .

A beautiful place, and emerald green, but to much rain for my taste north of Ashland. I enjoyed Eugene the last time I stopped there. The town was awash in coffee houses. I hope it hasn't changed. The music on the radio around Portland is great, but the further south you go, the more Bible thumping I heard (on the radio). It all went away though, when I crossed into California.

Please read for comprehension.

A greenhouse is a structure with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming VISIBLE (capitals mine) solar radiation (for which the glass is transparent) from the sun is absorbed by plants, soil, and other things inside the building.

Got that? Visible, not infrared does the heating. It doesn't say anything about direct or indirect, just visible. Got it?

Almost none of the infrared portion of the electromagnetic spectrum can reach the surface of the Earth, although some portions can be observed by high-altitude aircraft (such as the Kuiper Observatory) or telescopes on high mountaintops (such as the peak of Mauna Kea in Hawaii).