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So far I heard two opposite opinions:

  1. Harmful: watering at noon would shock the plants.
  2. Helpful: watering at noon would help the plant at the most difficult hours.

And would the answer differ between planted and potted plants?

Sparkler
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3 Answers3

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The optimum time to water plants is in the morning, before any heat builds up - this gives time for the water to penetrate and be taken up so the plants are already well hydrated. Watering in noon day strong sun means you'll lose some to evaporation before it has much of a chance to help the plant. The next best time to water is the evening, after the heat has abated, and particularly as the sun is lower in the sky. In cooler climates, this might mean a slightly increased risk of fungal infection if the air is cold and the plants are too wet overnight.

Similar rules apply to potted plants, although they at least can have a container beneath to hold some water to give the soil in the pot time to wick it up before it evaporates completely. In very hot, dry weather, morning and evening watering may be required, particularly for smaller pots.

On the other hand, if plants are obviously in severe distress, wilting all over the place, then water should not be withheld until the evening or the next morning - but it's always best to apply the water to the soil at the base of the plant, not all over the leaves - it's the roots which need the water.

Bamboo
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  • so the only reason not to water at noon is that I'll just need more water to achieve the same effectiveness as in the morning? – Sparkler Jul 06 '15 at 16:43
  • more or less yes, provided you're watering the roots and not the topgrowth - unless you've got a plant that's sensitive to cold water. a few prima donna plants prefer tepid water, but the vast majority don't mind. – Bamboo Jul 06 '15 at 16:45
  • There may be some harm to young plants: http://www.telegraph.co.uk/news/science/science-news/7823032/Sunburnt-plants-myth-is-debunked.html – Sergio Parreiras Jul 06 '15 at 19:56
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    @SergioParreiras - I've said 'provided you're watering the roots and not the topgrowth' for various reasons, some related to the info in that article, as a general rule - the acceptability of water spray on foliage varies according to specific plants and their age – Bamboo Jul 07 '15 at 10:45
  • When it's really hot out and the plants are drooping despite having enough water, a noon time or after spritz to cool the plants and leaves down will often perk them back up. – Escoce Jul 08 '15 at 01:15
  • @Escoce, could you please expand your comment into an answer? – Sparkler Jul 12 '15 at 01:50
  • No it's really just a comment. Bamboos answer is a very good one – Escoce Jul 12 '15 at 01:51
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Watering plant at noon, in the sunlight will NOT burn the leaves. Leaf burn is a myth.

Water droplets on a leaf surface are not able to focus the sun's energy sufficiently to damage the leaves before the water evaporates.

Only some plants with hairy leaves can hold the water droplets sufficiently far from the surface and may cause burning; But hairy leaves tend to shed water, so droplets would be unlikely to stay on them long enough to do damage.

Samer_Azar
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I only have the time to water at lunchtime - l am in the central Mediterranean and it is hot in summer. My garden is thriving! No negatives.

Tezzz
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