GardenGates: Gardening, Design & Garden Landscaping by Jane Schwartz Gates

Tomatoes with red plastic mulch

If you are enthusiastic about growing the best fruits and vegetables you can, you’ve probably heard about the possibility of increasing the quality and quantity of tomato crops by using red mulch. There are lots of suppliers marketing red plastic or paper mulch to use in your vegetable garden and touting the successful results created by using this product. The question is how much truth is there to claims about red mulch? Does red mulch really work on tomatoes?

The concept is that the pigment system in plants (phytochrome) responds to specific red wavelengths of light. If these wavelengths are reinforced in a mulch covering, the belief is that the growth of a plant can be improved with better crop results.

Tests at Cornell University have shown somewhat unclear results.  Some tomatoes did show increased results with the mulch while others remained unaffected. One conclusion was that different tomato varieties respond differently and not all will benefit from a red mulch.

The report from Clemson University came in with a 20% increase in crop production. This is one of the better recommendations for using red mulch.

Montana State University found plants tested with red or silver plastic mulch were more productive and set fruit earlier than plants tested with other treatments.  The overall conclusion was that the biggest difference was seen where seasons are short. Perhaps the improvement can be attributed to the warming of the soil or it may be a direct result of the color wavelengths. More research is still needed and tests continue.

The tests reported by the University of Connecticut and Penn State stated: there was “no significant difference in the yield of marketable tomato fruit from clear, yellow, black, silver, red or brown IRT mulch”.

Testing results at the University of Minnesota reported a 10 – 30% increase in tomato yields with red mulching, however.

Less confident about the results is the University of Vermont. The studies there were declared inconsistent and very variable depending on tomato varieties, sunlight levels and temperatures. Like other studies, the warming of soil temperatures did increase early fruit production and later plantings seem to have little to no impact comparatively.

Other discoveries are that different colors seemed to impact different vegetables. Red seemed to be the best for tomatoes.  And yellow seems to consistently attract insects. This means you probably shouldn’t use yellow mulch unless you plan to use it to attract insects as a way to trap them in a predetermined area.

Red mulch is being offered at many suppliers with claims of huge increases in productivity in tomato crops. So far it looks like most tests show there can be some improvement in the growth of many tomato varieties. But there is still more testing needed and there is no guarantee red mulch will benefit your crop of tomatoes, especially if you have a long, warm growing season where early warming of your soil is not likely to impact the success of your tomato growing.  The jury is still out.

But then, that might make testing your own tomatoes even more fun to see if you notice an improvement with red plastic or paper mulch. It looks like different climates, situations and plants all respond differently. Who knows? You might find the truth about tomatoes and red mulch in your own garden is the best news yet.