Watering plants in the midday sun scorches the leaves
Watering plants in the midday sun scorches the leaves (water droplets focus sunlight like lenses).
Watering in the midday sun won't scorch your leaves. Droplets don't focus sunlight on ordinary leaves. Water whenever the plant needs it, and aim at the soil and keep the leaves dry, because wet foliage invites fungal disease. Morning or evening watering just loses less to evaporation than the middle of the day.
What is actually known
Water droplets on a leaf do not focus the sun into a burn. On smooth, hairless leaves, sunlit drops of every shape caused no burn damage in a controlled optics study, and wet foliage is not prone to sunburn. The rare exception is a leaf whose water-repellent hairs hold a round drop just above the surface, as on a floating fern. There the drop can focus light and, out of contact with the leaf, no longer cools it. Hundreds of studies of leaf scorch have never pinned it on midday watering. What timing does affect is efficiency. Watering in the heat of the day loses more to evaporation than morning or evening watering, though evening watering can help fungal disease take hold. That is one more reason to put the water on the soil and keep it off the foliage.
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
Leaf damage can occur due to many causes: too much or too little moisture, insect damage, disease, over-fertilization, and weather conditions such as wind or frost, not sun scorching.
Hundreds of scientific publications on crop plants, turf, woody shrubs and trees have examined foliar scorch, and not one of them has implicated midday irrigation as a causal agent.
Contrary to popular belief, water droplets on leaves do not magnify the sun's energy.
… sunlit water drops, ranging from spheroid to flat lens-shaped, on horizontal hairless leaves of Ginkgo biloba and Acer platanoides did not cause burn damage
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Milpa Gardens. “Watering plants in the midday sun scorches the leaves (water droplets focus sunlight like lenses).” Evidence grade: Refuted. https://milpa.garden/beliefs/watering-midday-water-droplets-burn-leaves/
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