Myth debunked. Plants are not harmed by watering in the mid-day sun.

Generations of gardeners belived you should never water your plants in the full glare of the midday sun because the droplets act like tiny magnifying glasses and burn the plants.

Computer modeling and tests on plants found that water droplets on a leaf surface were not able to focus the sun's energy sufficiently to damage the leaves before the water evaporated.

Some tropical plants with hairy leaves where the water droplets are held sufficiently far from the surface can cause burning, but hairy leaves tend to shed water, so droplets would be unlikely to stay on them long enough to do damage.

Dr Horvath speculated that drops of acid rain, salty sea or tap water, chlorinated water and concentrated solutions of fertiliser or other chemicals can all cause sunburn-like brown patches that created the myth.