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Is it bad to water plants after the sun has gone down or near dusk? If so, why?

Jim Geurts
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    I would think plants have evolved to deal with water at any time of day, at least in climates where rainfall can occur at any time. – JYelton Jun 23 '11 at 21:26

7 Answers7

48

An advantage is that you can conserve water because of less evaporation -- there's no sunshine.

A major disadvantage is the flip side: the sunshine can't help dry out plant leaves that get wet. Some plants don't like cold and wet foliage. These conditions can foster blight on tomatoes for example. See also this answer that mentions being careful not to leave basil damp overnight.

So if you're watering in the evening, don't spray the foliage. Use a soaker hose or other irrigation technique that targets the roots instead of the foliage.

Early morning is a good time to water. You can give the soil a good soaking and everything has a chance to penetrate before being burned off by the sun. Anything that gets on the foliage will dry up with the sun and you're less prone to disease and fungi.

Community
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bstpierre
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  • I hadn't thought of the mould/blight problem, and I don't think I've seen it outdoors: I would think this is probably only true with cold nights and specific plants? – winwaed Jun 15 '11 at 20:45
  • @win - All we have are cold nights, except for maybe a day or two in August! Reading the other answers, there are *definitely* local considerations here. – bstpierre Jun 15 '11 at 21:16
  • Yes - my conditions are more comparable to @baka's; whilst I've seen slugs they're not common, and definitely not as common or large as Northern England (@mancuniensis)! – winwaed Jun 15 '11 at 21:24
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If anything, the opposite is true. There are two reasons:

First is evaporation. During the day it is hot and the water evaporates quickly - i.e. it is effectively wasted. This is why cities and water authorities have recommendations, regulations, and by-laws controlling when you can use landscape irrigation systems.

Secondly, water on plants in the sun can cause scorching - regardless of your latitude. This is because the water droplets act like small lenses, concentrating the sun. So you really want the water to be off the plants when the sun is out. This usually makes the evening at sunset (or after) more favorable to early morning watering. Of course drip irrigation is another way of avoiding this problem.

winwaed
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    Apparently the scorching common wisdom may be false: http://www.telegraph.co.uk/science/science-news/7823032/Sunburnt-plants-myth-is-debunked.html – kmm Jun 15 '11 at 23:22
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    The thing is, we see scorching (or I do), and the explanations put forward in that article don't cut it. Salt, fertilizer, and acid rain splashes are not likely on the plants where I've seen it. Perhaps the mechanism is different but water & sun appear to be a part of the cause. I also note at the end of the news item, that the chap from Kew says young plants could still be susceptible to scorching (off the top of my head, I think young plants/seedlings and succulents are where I've seen it in our garden here) – winwaed Jun 15 '11 at 23:56
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    Question posted on Skeptics.SE: [Is watering plants under a hot sun bad?](http://skeptics.stackexchange.com/q/2853/43) – JYelton Jul 11 '11 at 23:24
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    Water acting as a lens which burns plants simply isn't true. If that were true, then water drops would burn humans as well, which it clearly doesn't. – Randy Aug 04 '13 at 04:25
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    There is a huge variety in plant tissues - and all are different to human epidermis. – winwaed Aug 07 '13 at 21:46
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It is true that watering when the sun is out can cause scorching; on the other hand, although evening watering reduces evaporation, it leaves plants and the surrounding soil wet, or at least damp, at nightfall; besides providing fertile ground for diseases, this attracts more pests, particularly *slugs.*

Mancuniensis
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    Its not true that watering when the sun is out can cause scorching. – Randy Aug 04 '13 at 04:28
  • Can you provide a source for that? I have never experienced scorching from water droplets on the leaves whatsoever. – Jan M. Jul 17 '18 at 10:48
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This link favours watering in the morning and, if that's not possible, then late afternoon (with enough time for the plant to dry out a little).

The dangers associated with scorching (daytime watering), are far outweighed by the problems associated with damp sulky plants (nighttime watering).

Tea Drinker
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8

Here in the American South, in the summer, it's actually better to water plants in the evening, so that the water has a chance to soak in before it evaporates.

baka
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    Would it not be even better to water at 5am/6am just as the sun is rising (assuming it's easy enough to do in your situation)? – Lisa Dec 14 '11 at 04:48
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It is only better to water in the evening or early morning from a conservation perspective due to evaporation of this precious resource.

Otherwise, the idea it's bad to be watered under the bright midday sun because it hurts the plants themselves appears to be a myth. See this article by a well qualified horticulturist debunk it.

There are many causes of leaf scorch, but irrigation with fresh water is certainly not one of them. 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. What does cause damage, however, is suboptimal plant-water relations, which can result in tip and marginal leaf scorch, shoot dieback, stunted growth, and leaf abscission.

Lisa
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  • For anyone interested, I also cross-posted the link to Chalker-Scott article in answer to [Is watering plants under a hot sun bad?](http://skeptics.stackexchange.com/questions/2853/is-watering-plants-under-a-hot-sun-bad]) on Skeptics.se. – Lisa Dec 14 '11 at 05:39
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Indeed, the best time to irrigate is in the morning and in the late afternoon for moisture to be absorbed by the plant with minimal evapotranspiration.

Alina
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Enock Mthreheya
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