I've apparently been watering under a misapprehension. I always thought the logic behind hosing down plants in the cooler hours was that a midday jolt of frigid water might "shock" them. I never considered that dewy beads of water could magnify high noon rays and literally burn leaves. Because that just sounds too bizarre to be true, right?
Apparently not. According to LiveScience (via io9), the gardener's tale of fire-starting, leaf-singeing water droplets has finally undergone scientific study. Biophysicist Gabor Horvath at Eotvos University in Budapest and colleagues set out to test the theory through experiments and computer modeling. What they found out had a lot to do with leaf type.
Plants with finely haired leaves, like those on the floating fern, suspended water droplets above the leaf's main surface. This small gap of space was just enough room to make the droplet act like a magnifying glass, concentrating sunlight and burning the leaf (although not to the point of fern-engulfing flames). However, smooth leaves, like those of a maple, were unaffected.
But could the properties that singe your petunias also start forest fires from dried-out leaves? Horvath says that's still fairly unlikely: "If the focal region of drops falls exactly on the dry plant surface intensely focused sunlight could theoretically start a fire. However, the likelihood is reduced as the water drops should evaporate before this."
The more likely victim of droplet burn is your own finely haired skin (I've never thought of myself in relation to a fern before). The researchers reason that the magnifying effect of droplets could make your sunburn worse.
Thanks to FanStuff's Tracy for passing this on