Lexan or not ?

The roof goes up on Weezin"s new greenhouse this spring.

Now I'm looking for feedback on "Lexan" or similar polycarb
product.

It came up from a friend whos GH is covered in Lexan. 1 st.
her tomatoes wont ripen and 2nd when she trys to take a picture with her digital camera in the GH the light sensor tells the camera to fire the flash. Even though its so bright inside you have to squint your eyes.

We have no problem get our tomatoes to rippen in our fiberglass GH or in our raise beds with hoop covers.

Befor I spend several thousand on the lexan I like to know if it block light spectrums beneficial to growing plants.

All feedback welcome................Dennis.........

polycarbonates block UV light so if you need the UV portion of the spectrum to be transmitted for the plants to use it might not be a good choice.

This is an apapted version of a post I placed in another thread:

Your question about the use of Lexan or other greenhouse covers is a subtle one, and the answer isn't entirely simple.

Both UVA and UVB radiation, which are invisible to the human eye (at a frequencies shorter than 400 nanometers), are "visible" to plants to a small degree, and the energy they derive from them does play a part in plants' metabolic activities.

In order to optimize plant growth you need a greenhouse cover material which either passes or at least does not "interfere with" that radiation frequency.

A transparent or translucent material such as a greenhouse cover, ought not to reflect the longer~wave UV radiation, as it should be optimized to admit the widest possible spectrum of light to enhance plant growth.

However, as life teaches us, some things are sold or bought for purpouses they are not intended.

To help you find your perfect greenhouse cover, it is good to know that there are two types of chlorophyll at work in every green plant: A & B. Each makes use of slightly different light (energy) frequencies to support plant metabolism.

Both types of chlorophyll rely heavily on light in the red range of the spectrum, 600 ~ 700 nanometers. And both types rely, to differing extents, on light in the range of 350 ~ 500 nanometers.

Wavelengths 400 nanometers and smaller are at the beginning of the UV portion of the frequency spectrum. Human vision cuts off at frequencies below approximately 400 nanometers. However, as we see above, some energy at the upper range of UV (350 ~ 400 nanometers), is required for plant growth.

I would bet a dollar, as you research potential greenhouse covers, that the reliable sellers of these materals "rate" their products by frequency, so that you can pick one that best suits your growing needs.

I hope this helps.

Adam.

PS: I'd bet you can now "see" why the camera senses less or different light than your own eye.

This message was edited Monday, Mar 3rd 1:36 PM

This message was edited Monday, Mar 3rd 1:54 PM

Thanks, Adam. That's a thorough explanation. I've printed it out for my DH to read. Thanks for helping out. Thanks to Kikisdad, too.

Came across this info and thought it would be helpful.http://www.hobby-greenhouse.com/lexan.htm

Soon be mater planting time up there, I'm sure! *wink*

Horseshoe ~~~

Thank you for the excellent link.

That website says:

"Reduced Ultraviolet Transmission
Lexan Corrugated sheet is grower friendly. While it transmits a high portion of visible light, it is essentially opaque to ultraviolet light at wave lengths below 385 nanometers. Lexan Corrugated sheet blocks out the harmful UV light."

Any introductory botony textbook will tell you that both chlorophyll A & B make use of UV light at wavelengths below the "385 nanometers" cited above to support plant metabolism and growth.

I am not saying that Lexan is a bad product. I am saying that we ought to recognize its limitations and balance those against its excellent characteristics.

As you carefully read the sales language in the site Horseshoe found for us, they made a benefit for the gardener out of a negative for the plants... Lexan blocks UV light!

The reality is, nothing man can make will equal the light passing ability of the atmosphere. A greenhouse is a trade off..., we get to control the environment a little bit and the environment gets to extract something from us as payment: it takes back some UV radiation.

Adam.

Is there any way to make up for this loss by installing some sort of "special" light? Or is there any such animal? I'm not talking about grow lights (or would those work to make up for the loss of the UV?).

Hi, Wingnut. Dennis is busy repairing a ToyoStove, so I'll make some lame reply! We bought a large halyde light last year, and all the plants certainly loved it. However, it cost over $50 per month just to run it. I'm making the assumption that you don't use greenhouses in the summer where you are... unless you bake bread in them! LOL. Here we use them all summer to grow the things that don't do well in our cool summers, such as tomatoes, peppers and cucumbers. In other words, a special light that gives my plants a full spectrum of light (or a better one), would be cost prohibitive.

I think that Adam has hit on an important point. Nothing beats Mr. Sun... unfiltered and strutting his stuff. But, when necessary, we have to protect our plants and take what we can get... i.e., grow lights, fluorescents, greenhouse materials, etc. If you want to build a solarium where you can read a book or house your hot tub, a full spectrum of light isn't an issue... Lexan would be great. But if your only reason for constructing with it is to grow plants, I don't know that it is worth the heavy expense when something else cheaper would give you the same results.

Yeah, don't need ANOTHER oven so when I finally get the greenhouse done I figured I'd just keep it empty in summer, but still closed up so it'll kill any pests and diseases by baking. ;) But in winter, it sure would be nice to have three or four tomato plants back in the corner for fresh 'maters all year long! :) Fifty bucks a month, huh? YIKES! But Kenny would surely think it a good investment as he heads out there with a salt shaker. ;) Thanks, Weez!