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market-farming - Re: [Market-farming] Plastic Mulch

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  • From: "Bill Shoemaker" <wshoemak AT inil.com>
  • To: "Market Farming" <market-farming AT lists.ibiblio.org>
  • Subject: Re: [Market-farming] Plastic Mulch
  • Date: Fri, 21 May 2004 08:08:20 -0500

Allen

Plastic mulch has several different features that can be useful to
farmers. It can conserve moisture and provides excellent weed control,
particularly if it's black. But it's primary value is how it interacts with
light and influences heat around the plant. The most common plastic mulch
comes in the color black. When used, it converts the light that hits it to
heat, building soil temperature up and increasing air temperature around
small plants. As plant grow and reduce the amount of light hitting the
mulch, the effect diminishes. As the plant canopy grows enough the intercept
90% or more of the light that would hit the mulch, the effect largely
disappears. At that point the mulch is just providing moisture and weed
control. But the primary reason most growers use it is to give young
transplants a bath of warm temperatures early in the season and a stable,
protected environment. It's very effective and worth the expense with
hi-value crops.

Plastic mulch can come in many colors, including clear mulch. They
differe in how they interact with light. Clear mulch allows light to pass
through. The light hitting the ground underneath converts to heat and the
heat builds up under the mulch more than with black. Crops like cucumbers
and melons will grow even faster than with black plastic. But weeds under
the mulch will also grow. They can push the mulch right out of the ground.
growers in the north have learned that if you seal every opening in the
clear mulch with soil (like around the holes you make for the plants), the
air under the mulch will not ventilate and the weeds will burn off. The
plants you put in will do fine, particularly cucurbits, which love heat.

Other colors are used to create other effects. White mulch is used in
the summer in southern states to cool the soil. It reflects all light
wavelengths meaning no light hits the soil to heat it up. Red mulch reflects
only the red wavelengths back up into the canopy, which means the plants are
exposed to a greater degree of that wavelength of light. With tomatoes that
means stouter, shorter plants that flower and fruit earlier. Green mulch
means that all wavelengths of light but green pass through the mulch,
heating it up more. The green bounces back up, boosting plant growth. Yellow
mulch attracts insects. Blue mulch makes plants sad (just joking).

Another version is reflective mulch, which is like a plastic mirror. It
affects plant growth but it also makes an oppressive environment for
soft-bodied insects like aphids. I've been working with it to see if we can
reduce virus (which is vectored by aphids) incidence in pumpkins and squash.

Anyway, plastic mulch does very interesting things due to it's unique
properties. But it also is a problem for sustainability. It does not break
down and if not removed, it can last in the soil for hundreds, if not
thousands of years. So it should be removed. There are attempts to makes it
biodegradable but those efforts have not panned out very well. Some
promising science is around but as yet it is unfulfilled. Photodegradable
mulchs will break down after exposure to light for a while but there is
always some of the mulch that is buried. It will not break down until it's
exposed to light for a period of time, usually months. In the meantime, it
gets caught in machinery and can blow in the wind. The real answer for now
is removal and recycle. But not all recyclers will take it due to the dirt.
Go to a search engine and look for the American Society for Plasticulture
site. It'll tell you more.

Bill Shoemaker
Sr Research Specialist, Food Crops
Univ of Illinois - St Charles Hort Research Center



-----Original Message-----
From: Allan Balliett <igg AT igg.com>
To: Market Farming <market-farming AT lists.ibiblio.org>
Date: Thursday, May 20, 2004 11:06 PM
Subject: [Market-farming] Plastic Mulch


>Coming up on the biointensive side, I've never had a chance to
>develop a feel for using plastic mulch, nor have I seen any writeups
>on using it in any of the organic gardening books I commonly use.
>
>What's really keeping me confused is using plastic with organic
>mulches, like hay, or whatever.
>
>What's the deal with this? Do you monitor soil temps and start piling
>on hay mulch to keep them below 100?
>
>How would you, oh Chile Man, typically mulch peppers with plastic?
>(And will you use it THIS year?)
>
>I'm in the Mid-Atlantic region, where it can get very hot for weeks
>at a time. Is it likely that if I used plastic mulch that there will
>be crops that I can plastic-only and not have to re-mulch with hay
>for coolness 'later' (It's august already here)?
>
>Thanks -Allan
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