Red plastic mulch was actually not introduced as mulch. Rather, its developers (USDA’s plant physiologist Michael J. Kasperbauer and Clemson University nematologist Bruce Fornum) found that it increased yields up to 20%. It was first recommended to commercial farmers, rather than home gardeners, who could benefit from higher production on a larger scale.
Along the way, gardeners began referring to red plastic tomato mulch as a mulching option.
While the product is not technically mulch, it’s increasingly used as one. Red plastic mulch (also known as Selective Reflecting Mulch, or SRM for short) is similar to black plastic mulch in that it warms the soil, prevents erosion, and retains moisture. It’s thinner than most garden plastic, allowing more light (and sometimes weeds) through.
But red plastic mulch’s touted strength is in its ability to reflect certain red shades of light back into the plant, accelerating fruit production and increasing yield.
There are pigments in tomato plants called phytochromes. They are color-sensitive proteins. Their job is to regulate plant growth and development.
Phytochromes react differently to different spectra of light. Specifically, when far-red light wavelengths from the plastic bounce back up to tomato plants, the phytochromes tell the tomato fruit to grow more and faster.
That’s why gardeners say setting out red plastic mulch around their tomato plants makes their tomatoes ripen faster and produce bigger fruit.
Naturally, the amount of light reflected depends on growing conditions. Also, the plastic color must be specific. In other words, just any color of red plastic may not give good results, but rather those which have been developed and tested for this purpose. Recent studies suggest that other colors of plastic may offer greater yields than black, too, particularly blue plastic.
Additional studies have documented that red plastic mulch also reduces nematode damage. Nematodes (specifically, root knot nematodes) are worms that feed on a tomato’s root system. They are a particular problem in areas where the ground does not freeze, because they continue to live in the soil all year long.
A study by the USDA’s Agricultural Research Service found that red plastic mulch suppresses root nematode damage to tomatoes because the light reflection keeps more of the plant’s growth above ground. The plant’s energy goes into developing fruit and foliage, rather than roots. Nematodes feed on roots. The far-red light reflection to the above-ground plant draws away nutrients from the roots – and nutrients away from the nematodes. Fewer roots mean less food for nematodes. Less food = fewer nematodes.
Red plastic is available to home gardeners in rolls of various lengths. If you look hard you can find it in oversized squares, which is well suited for container tomatoes or for gardens with just a few tomato plants. If you have a larger number of tomatoes, rolls are the more economical choice.
(Browse different types of red plastic mulch.)
More than four out of five gardeners who use red tomato mulch would recommend it to a friend. Even so, there are some cautions.
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