greenhouse shading

Jim Perry jperry at UWC.EDU
Sun Feb 14 11:56:15 EST 1999

My university has just built three new greenhouses with exactly the same
circumstances as have been described. I was intimately involved in the
process, both as a botanist, but perhaps more importantly as the Chief
Executive of the campus, weighing the cost against the aesthetic factors.

I would advise very strongly against uses of anything but glass. I can't
imagine the C4 plants receiving sufficient illumination any other way.
While more expensive in the short run, glass will be much less so in the
long run. Ours is double glazed, so it has good insulating properties. As I
have in the past, I invite anyone to call me to discuss our "experience." I
will not commit it to e-mail. We are very happy with the product, but
getting there is something that I am willing to discuss in person. Quite
candidly, you WANT to talk with me (even if you don't know it).

We solved our aesthetic problem (our greenhouses are on the front of the
building along the main thoroughfare -- how's that for putting botany 'out
front'?) by using external aluminum shades. They are slats that roll up
into cylinders at the top of the greenhouse when not deployed. These look
quite nice, but if you are thinking of deploying and rolling up on a
regular basis this is not for you. We put them down in the later spring and
roll them up in the fall. A few stay down all winter, over areas where we
desire continually reduced shade. Each section is 4 feet in width. On the
high hose, the total length of each unit is about 20 -25 feet. There is a
cable system that allows them to be rolled up. One needs to be careful when
rolling them  up, because adjacent sections are separated by only a couple
of inches, so they need to form an almost perfect cylinder when rolled up,
without any edges sticking out. Our greenhouses have side vents, and we
decided to end the shading above the side vents so the shades would not
interfere with the vents.

There are internal, motorized systems (UW-Madison Department of
Horticulture has such a system) that consist of shade cloth. The reason we
did not use that system was because of cost and the need for having very
high intensity supplemental illumination for our dreary winters. We could
not figure out how to suspend lights from the ceilings and have this
motorized system function effectively.

I would be willing to send digital images via e-mail to anyone who
expresses an interest.

Hope this is of assistance, and good luck.


At 12:29 PM -0800 2/13/99, John Sowell wrote:
>Dear Plant Ed'ers:
>We are in the process of designing a new greenhouse and working with the
>architect to choose the appropriate glazing. The greenhouse will house the
>teaching collection (including tropical understory/epiphytic angiosperms,
>cycads, seedless vascular plants, bryophytes, lots of geraniums, and some
>cacti) but will also be used for growing plants such as grasses, beans,
>etc., (some of which are C4) for experiments in general botany and plant
>Our current greenhouse has shaded glazing that allows transmission of about
>70% of full sunlight. In addition, whitewash and shade cloth is used over
>much of the collection which lowers the total transmission is about 20-30%
>full sun. This has worked well because when growth of experimental plants
>is required, a portion of the shade cloth is remove and the plants (even
>corn) seem to do just fine with 70% of full sun.
>The problem is that the new greenhouse will be in a more obvious location,
>attached to the building, and it would be aesthetically desirable to lessen
>the need for shade cloth. The architect has proposed using a white
>translucent glazing that allows 35% to 50% (our choice) transmission of
>full sunlight. This would be great for most the teaching collection but
>what about the growth of experimental plants? Is etiolation a problem? Is
>there anyone out there that has such a greenhouse and is now regretting it?
>Thank you for your input.
>John Sowell
>Professor of Botany
>Biology Department
>Western State College
>Gunnison, CO 81231
>jsowell at

James W. Perry
CEO/Campus Dean
Professor - Biological Sciences
University of Wisconsin-Fox Valley
1478 Midway Road
Menasha, Wisconsin  54952-8002
FAX 920.832-2674
jperry at

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