It's part of the entrenched mythology of the gardening world: if you water your plants in the hot midday sun, the droplets can act as a magnifying glass and burn the leaves. But until now, science had been unable to confirm the folklore as fact.
"The problem of light focusing by water droplets adhered to plants has never been thoroughly investigated, neither theoretically, nor experimentally", said Dr. Gabor Horvath of Hungary's Eotvos University.
Determined to discover the truth, Horvath and his team of researchers conducted a series of computer and experimental studies on the problem, with surprising results. The studies confirmed that plants can be sunburnt from water droplets — and people can too.
The connection lies in the types of plants most susceptible to getting burned. It turns out that water droplets on a smooth surface, such as maple or ginkgo leaves, cannot cause leaf burn. But plants with hairy leaves, such as the small wax hairs of floating ferns, tend to hold water droplets in focus above the leaf surface, magnifying the sunlight. The same principle holds true for water held above hairy human skin after bathing.
Researchers also considered if the same process could potentially start a fire if the light-focusing occurred over dried-out vegetation, but their results were mixed. While fires are theoretically possible, there are some natural factors that make them less likely.
"The likelihood [of a fire starting] is reduced as the water drops should evaporate before this, so these claims should be treated with a grain of salt," concluded Horvath.
Nevertheless, the study was clear about what gardeners and poolside loungers have long known. During times when the sun is most intense, it would be wise to keep yourself and your plants dry.