Competition for light makes plants see red
Have you ever noticed feeling different in different rooms? A room painted with red walls can make you feel energised or excited, while a room with blue walls can promote calmness and relaxation. It turns out the same could be said for plants and animals in the garden. Researchers at the US Agricultural Research Service in South Carolina discovered that red plastic mulch (plastic sheeting) can energise your tomatoes. Also known as selective reflective mulch, it can produce up to 20 per cent higher yields than tomato plants without it. This is not a new study. I remember the idea of red plastic mulch being bandied about six or seven years ago when I was editing Weekend Gardener magazine. At that time plastic mulch wasn’t readily available, but you can now get it online. So how does that work? Well, just like you and me, phytochromes, which regulate growth and development, react differently to different colours (wavelengths in the light spectrum), particularly in the red or far-red range. Light reflected from the red mulch has a lower red to far-red ratio than normal sunlight. When the far-red light wavelengths reflect off the red plastic mulch onto the tomato plants, the phytochromes kick into action and tell the plant to grow faster and produce more. The reason for this is that far-red wavelengths are not photosynthetically active. In other words, they don’t fuel plant growth. Instead, they enable plants to react to the environment. Green leaves reflect far-red light, so if there are a score of other plants nearby, a tomato plant will sense a high ratio of far-red to red light. In effect, its sensing competition for sunlight, which prompts it to put on a growth spurt so that it can better compete for light. By laying down red mulch the researchers discovered they could effectively trick the tomato plants into believing there was a lot of competition close by and induce faster growth. The same researchers trialled red plastic mulch beneath strawberry plants and found the plants to produce a higher yield, larger berries and a higher sugar content. They also reported that a blue plastic mulch under turnips produced a stronger flavour whereas a green mulch produced a mild, almost sweet, flavour. Other research suggests that a green mulch was good for peppers and melons, while a blue one benefited eggplants. Bear in mind that coloured mulches may work better in different parts of the country, however. Research at the University of Florida found that red, green or blue plastic mulch gave no benefit to crops in that state. They concluded that coloured mulches worked better in cooler parts of the country.
What's your wavelength?: Researchers at the US Agricultural Research Service in South Carolina discovered that red plastic mulch laid under plants, including strawberries, can produce higher yields.