Mylar on top of soil... bad idea?

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Aug 16, 2005
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So, I thought I'd try to bounce some light up under and to the sides of my plant by putting cut-to-fit pieces of mylar on top of the soil in my 7-gal growing pot. It's working -- rays of MH light are piecing deep and bushy areas from beneath.

Question is... is this a bad idea? I've never seen anyone else do this. Why not? Heats up soil too much?
Max, actually before i thought about the same thing but never done it. I don't think it would really make heat difference.
A. Leaves have no light receptors on their undersides.
B. Soil needs to "breathe". Placing objects such as mylar etc. on top of the soil restricts aeration.
Thanks, guys.

What's happeneing is that deep leaves and branches are being pierced with light from beneath. Photons are coming at the plant from below, but it's so bright, that the light is passing through these leaves and is visible from the top. So, photons seem to be "touching" the tops of the leaves, even though their angle of approach is weird. This won't allow for photosynthesis?

The mylar pieces are placed loosely above the soil, so it seems like there's room to breathe, but I can easily see how aeration would be restricted. Okay. Thanks again.

This mylar I have is doing such a good job, it's tempting not to want to use it everywhere.
Not ecactly "Mylar", but reflected light from beneath can be beneficial...
from... Findings on How Mulch Color Can Affect Food Plants.htm

Plant physiologist Michael J. Kasperbauer made a career of "seeing" light the way plants do: in wavelengths, some of which cannot be detected by the human eye.

The concept of colored mulch sprouted when Kasperbauer wondered whether phytochrome was equally distributed in leaves. He became curious about what would happen if light impinged on the leaf's lower, rather than upper, surface. "The plant response was the same, no matter which surface received the light," says Kasperbauer. "Although that experiment seemed somewhat unconventional in 1962, it became highly relevant about 22 years later, when we determined that red and FR reflected from the soil surface could act through the plant's phytochrome system to enhance yield and quality.

This unique perspective led to studies in which Kasperbauer—who recently retired from ARS' Coastal Plains Soil, Water, and Plant Research Center at Florence, South Carolina—headed development of colored plastic-sheeting-type mulches that increase food and crop plants' yield and quality.

His best-known work involved tomatoes and strawberries. In research done with Clemson University, he and ARS soil scientist Patrick G. Hunt found that tomato plants grown over red mulch yielded about 20 percent more fruit than those grown over standard black mulch. He later found that strawberries grown over red mulch smelled better, tasted sweeter, and yielded more than those grown over black mulch.

This research, started during the 1980s, led to development of SRM-Red, a selective reflecting mulch that has been available commercially since 1996.

Recent Findings in Carrots, Cotton, and Basil

Recently, colored-mulch studies have focused on how different wavelengths of light affect roots, stems, leaves, fruit, and seeds of many other food and crop plants. Kasperbauer and colleagues found that some colors enhanced plant products' flavor, aroma, and nutrient content.

They found that concentrations of nutrients and compounds such as beta carotene and vitamin C in the roots of food crops could be modified by reflecting the right waves of color onto the plants' leaves. This was demonstrated in carrot plants. The carrots were grown in trickle-irrigated field plots mulched with plastic sheets colored a shade of yellow that reflected low levels of blue light coupled with high amounts of red, far-red (FR), and photosynthetic light.

Beta carotene, a provitamin found in plants and their pigments, is a benign source of vitamin A and is an antioxidant with possible anticarcinogenic properties. Vitamin C helps maintain capillaries, bones, and teeth; assists in iron absorption; and is vital in the formation of a protein that gives structure to bones, cartilage, muscle, and blood vessels.

In another study, Kasperbauer discovered that cotton fibers grew longer in bolls exposed to increased FR-to-red light ratios. Length is an important component of cotton fiber quality.

"We set out to see whether cotton fibers would be as responsive to extra far-red light as the elongating cells in seedling stems are," says Kasperbauer. "We found that the difference in fiber length was influenced more by the higher FR-to-red ratio reaching the developing bolls than by increased photosynthetic light."

He concluded that the FR light reflected to developing cotton bolls can penetrate the boll walls to reach the developing fiber within and influence elongation.

Kasperbauer also headed studies with basil, which revealed that the amounts of blue, red, and FR light reflected onto developing leaves affected their size, aroma, and concentration of soluble phenolics. Phenolics are naturally occurring compounds that include tannins and pigments. They induce—among other properties—color, some flavors and odors, and antioxidant activity.

The basil was grown over six colors of polyethylene row covers. "Leaves developing over red surfaces had greater area, succulence, and fresh weight than those developing over black surfaces," says Kasperbauer. "Basil grown over yellow and green surfaces produced significantly higher concentrations of aroma compounds than did basil grown over white and blue covers."

The leaves grown over yellow and green mulches also contained significantly higher concentrations of phenolics than those grown over the other colors.

Colored-mulch technology relies greatly on "fooling" plants into behaving as if they face stiffer competition for sunlight than they actually do. This is achieved when they receive high amounts of FR light. Plants reflect FR and sense reflected FR to gauge how close and dense other vegetation around them is. To stay ahead of what's perceived as increased competition, they develop larger shoots.

Kasperbauer says the colored-mulch technology's controlling factor is not the perceived colors themselves, but how they change the amount of blue and the ratio of FR to red light that plants receive.

another link...
Colored Mulch info
Max said:
This mylar I have is doing such a good job, it's tempting not to want to use it everywhere.

I do have mylar pretty much everywhere surrounding my plant except for space for good ventilation but I find that with lots of mylar reflecting all the light from different directions it seems like it makes the light bounce simply bounces around in my little grow area which is amazing considering last year i used mylar and only had an 80 w fluoro and with the mylar and good fertilizers I harvested 1.5 Os from one plant. this year I have 285 watts, 125 watt solux red light and 2 80 watt dbl gro lux fluoros with more mylar and even better fertilizers so I cant wait to see what I harvest, although it is going a bit slower because I made a very very rookie mistaking by pruning leaves in late veg, but now thanks to you guys I know better! Anyway my point is mylar is definatly the way to go!
Hick!! Thank you so much for the excellent and well-researched reply.
Sorry for not responding sooner, especially since you went to so much trouble to answer my question.

Anyhow, looks like I'll have to find some of this red soil and give it a try in my next grow.

Same strain, three females (hopefully)... one with red, one with mylar, one with nothing. Will see which one does the best.

Insane --

Yeah, I've been pleasantly surprised with Mylar too. Makes me want to try some of those nylon based reflectants. They're supposedly even better than mylar.
I found it .."enlightening"...too, MAX. :p Was thinking it would be a worthwhile test, to run clones from the same donor, under identical conditions, but employ different colored mulches. See if the results indicated enhanced flavor, odor, yeild, and over which color.
I'm a "flavor" guy, so this would be important factor for me. I won't smoke it if it doesn't taste good. Potency is important, but secondary and yeild is least important to me. Quality over quantity anyday.
Influence the taste of something by the color of plastic sheeting on the ground?
My b.s. detector just woke up the whole neighborhood.

Sounds to me like the people who claimed that certain types of music influence growth, despite the fact that
-The best music for increased growth/yield was dependant on the type of music the "researcher" prefered. Fans of classical music said classical music was best, heavy metal fans said heavy metal was the best, etc.
-plants have neither ears nor brains to process music.

Back in the 70's there was a book called The Secret Life Of Plants, that claimed (among other things) that, with special microphones, you could hear trees scream out in pain when a branch was cut off. And that if you yelled at a plant, the plant would cringe whenever you entered the room they were in.

There is no reason whatsoever that the undersides of leaves would develop the ability to process light. It doesn't occur in nature.
As far as mulch is concerned, it makes sense that black plastic sheeting would aid growth for plants that start to grow in the winter (like strawberries). That's because black plastic absorbs sunlight and therefor heats the soil.
But using black plastic during the heat of the summer would heat the soil up so much that it would burn the roots off of most plants.

I remember one guy who posted @overgrow who said he sang Irish lullabye's to his plants as the lights went out. He said it increased growth and resulted in better taste and increased resin production.
He said he had proof.
GanjaGuru said:
Influence the taste of something by the color of plastic sheeting on the ground?
My b.s. detector just woke up the whole neighborhood.

Ha ha. And if I understand correctly, you live in a pretty sparsely populated neighborhood. :) It is true that plants have evolved and thrived over the eons without the use of pastel-colored soils.

GanjaGuru said:
There is no reason whatsoever that the undersides of leaves would develop the ability to process light. It doesn't occur in nature.

Hold on a second, Ganja. We aren't exactly buying that either. But I don't think it's reasonable to say that the electrochemical process of photosynthesis "cares" about the angle from which light approaches the plant.

As you know, there aren't really such things as "light receptors" that are perfectly placed only on the tops of leaves. It is NOT as if the plant will "ignore" light if it is coming at it from the bottom.

The cells in the *interior* tissues of a leaf (mesophyll) contain about half a million chloroplasts (green stuff, turns light into electrons and NADPH, etc.) for every square millimeter of leaf! Sure there are more chloroplasts towards the top of a leaf, (especially in the palisade mesophyll cells) but once the light gets in there, no matter where from, the electrochemical process will begin. I think.

Now your bullshit meter is really gonna go off: I think of plants as brilliantly designed organisms; kind of like organic examples of fractal design and mathematics. Like any function, they will respond differently to different kinds of input and that input does not have to be limited to everyday nature's repetoir of parameters. In other words, this red soil stuff just might actually work.

I'll let you know.... ;)
with special microphones, you could hear trees scream out in pain when a branch was cut off.
"I" don't need special microphones, but earmuffs are a must when I'm cutting firewood..;)

This isn't the only study/tests done with colored mulch/groundcover that supports the findings ganga'. There are independant studies done on similar colored mulches, useing different composition material from different manufacturers.
It actually seems at this point, to be more a question of "which" color or composit, is most beneficial, not so much a question "if" it does or not.

Phytochrome, which was discovered in a project headed by Harry A. Borthwick and Sterling B. Hendricks, is considered to be the universal regulator in plants. Plants sense the quality of surrounding light through chemical reactions in phytochrome.

Phytochrome exists inside plants in two interconvertible forms. One form absorbs only red light, which causes it to undergo a chemical transformation and become the other form. The other form will absorb only far-red, and then it becomes the other, red absorbing only, form. The ratio between the two forms in the plant depends on the ratio of far-red to red light and regulates the use of resources within the plant.
"The use of polyethylene mulch has increased dramatically in the last 10 years not only in Pennsylvania, but throughout the United States. In Pennsylvania, use of plastic mulch in vegetable crop production has gone from 7,000 acres in 1983 to about 25,000 acres in 1993. The increase in use of polyethylene mulch is due to its benefits when applied in the field: increase in soil temperatures especially in early spring, reduced weed problems, moisture conservation, reduction of certain insect pests, higher crop yields and more efficient use of soil nutrients."
"Colored plastic mulches, which are wavelength selective and/or reflective, are relatively new materials that have advantages similar to black or clear mulch. They let certain wavelengths of light through and absorb or reflect other wavelengths. Colored plastic mulches are made with different dyes and other enhancements to change their basic properties. They have additional benefits related to better management of soil temperature by allowing specific light wavelengths to strike the soil. The altered quantity and quality of reflected light in the plant canopy may influence plant growth and productivity."
"White reflects heating rays, producing cooler temperatures underneath.
That’s a boon for fall cauliflower or broccoli, which prefer cooler temperatures, Marvel says.
Metallized silver is another temperature-lowering option, Orzolek says. It also reflects enough light to confuse aphids, whiteflies and thrips, reducing infestations.
Tomatoes respond to red
That quality attracts tomato growers, Marvel says. But red—his biggest seller among all the colors—also offers benefits.
Tomatoes respond to the wavelengths reflected from red plastic by producing higher yields and larger plants, Orzolek says.
Growers also report faster maturation, especially with early varieties, Marvel says.
Blue is new
Blue mulch is one of the newer colors, and, like red for tomatoes, provides growth and maturity benefits to cucurbits, particularly squash, cucumbers and melons, Marvel says.
Florida tests, however, produced “wilty plants” from overheating, Fleck-Arnold says. “It can be too hot in some regions” for some colors, she says. “You’re just going to cook everything.”
Green also pushes vine crops such as cantaloupe and watermelon to earlier harvests, Marvel says.
Other crop and color combinations include metallized silver for potatoes, white or white-and-black for lettuce, and green or a metallized mulch for peppers, Orzolek says."

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