We need plants for food. Our livestock need them too. But we tend to focus only on what we can see when we’re growing them. Roots are critically important, and as summer continues to heat up, growers need to consider root health when caring for whole plants, whether they’re in the field or in the greenhouse.

Dr. John E. Erwin, professor and chair of the Department of Plant Science and Landscape Architecture at the University of Maryland, recently dug into this topic through a presentation titled “Improving Plant Growth, Resilience and Yield,” with support from FNRI and USDA-ARS.

According to Erwin, roots are the underappreciated limiters of growth, shippability and yield across a wide variety of plant species. “We grow plants with an incredible diversity of indigenous backgrounds – some are from prairies, some are from tropical locations – but what’s in common with all of them is we take them and put them into a pot and we restrict the roots in that pot,” he said.

It was noted that in the majority of greenhouse and nursery production, the pots used by growers are black, and so he and his team of researchers wanted to see how hot it actually became in those black pots. It turned out that the media temperature can actually be double the air temperature (in degrees Celsius).

The next thing they considered was what kind of impact that heating has, using tomatoes as their model plant. They heated a number of black-potted plants to different root temperatures and studied plant growth. The researchers’ data found that when root temperature went above 86º F, root dry mass started decreasing – “which tells us our loss of roots in the summer may not be from root rot but from roots getting too hot,” Erwin said. He explained that as temperatures got hotter, plants (and their roots) got smaller, and less photosynthesis took place.

Compounding this, Erwin continued, is the fact that the amount of oxygen in water decreases as temperature increases. “Not only are we killing roots with hot temperatures, but are we ‘drowning’ roots when we water frequently on hot days by filling media pore space with water with little oxygen?” he asked.

The results of this research led to Erwin recommending that when you do grow nursery crops, you do whatever you can to keep root temperatures cooler than you are now. He added that all the fungicide currently being applied may be unnecessary, because it might not be root rot causing all the problems.