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Some gardening sources recommend watering lawn in the morning, with the reason being water is needed for photosynthesis, and the grass can use it straight away after watering. Some sources say the evening is the best time as the water does evaporates slower when it is colder and there is no sun, therefore the water has more time to soak into the ground. To make it even more complicated, there is an argument against evening watering stating that grass staying wet through the night may increase risk of diseases (see Watering efficiently) .

From a water conservation point, which is better time for watering, morning or evening? Was there some controlled experiments done, with grass or other plants, with the goal of maximizing plant mass growth with a given amount of water?

If the best time is confirmed to be very early morning (that would probably make sense from the reasons above, but experimental evidence would still be preffered), but I am unable or not willing to do that, which of the easily available options (morning, evening, or both - with the amount split between them) is the best?

  • Duplicate of skeptics.stackexchange.com/questions/3755/… – going Jun 2 '11 at 8:32
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    While related, I do not think it is a a duplicate. I am not talking about watering during a day at all. Moreover, I am not concerned about water loss, but about optimum growth with given water budget, which may or may not be related. – Suma Jun 2 '11 at 9:27
  • @Suma - But is that a skeptical claim or just a gardening tip as mentioned in the other question. – going Jun 2 '11 at 9:51
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    There is a common gardening advice, which I am sceptical about, until proven by some evidence. I understand the question is about everyday subject, but I do not see how it would prevent it from being inquired sceptically. If you disagree, feel free to downvote or vote to close. – Suma Jun 2 '11 at 9:57
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    Good question to repost on gardening/landscaping SE when it goes live. – JYelton Jun 2 '11 at 20:34
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Answers provided from Lawn Watering from the EPA.

From a water conservation point, which is better time for watering, morning or evening?

Early morning watering will minimize evaporation and help newly seeded areas through the day’s heat.

If watering is done in the evening, grass stays wet all night, thus increasing risk of disease.

Was there some controlled experiments done, with grass or other plants, with the goal of maximizing plant mass growth with a given amount of water?

This is a separate question altogether: water conservation and plant growth are two completely different things. And now you are asking about plant growth and not about grass.

For grass only:

It’s best to water established lawns at the rate of one inch per week, applied all at one time to promote deep rooting.

And from Cleveland Turf Supplies:

The amount of water your lawn requires and receives will determine its overall health, beauty and ability to withstand use and drought. Keep in mind that too much water can ruin a lawn just as fast as too little water.

One inch (2.5cm) a week is a "watering rule of thumb" suggested for most lawns; however, this will vary between different turf species and even among cultivars of a species. There will also be varying water requirements for seasonal changes and still more differences brought about because of different soil types.

If the best time is confirmed to be very early morning... which of the easily available options (morning, evening, or both - with the amount split between them) is the best?

Well, if the best time is morning and you are not willing to do it in the morning, then the best option is still morning.

  • "This is a separate question altogether: water conservation and plant growth are two completely different things.". I think it is not. I was carefull to link those two things together by assuming the water amount fixed, and asking which time will give the best growth. Also, while I appreciate the answer, I would expect to get such answer on gardening site, but not here. Instead of following "common knowledge" I would really prefer some more scientific way how to determine the answer, as common knowledge is often wrong. – Suma Jun 3 '11 at 21:00
  • "It’s best to water established lawns at the rate of one inch per week, applied all at one time to promote deep rooting." <-- I've found no evidence to support that statement. Actually, I've found evidence to the contrary. See my question and answer here: gardening.stackexchange.com/questions/7761/… – Randy Jul 4 '13 at 2:27
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"The simple answer is at Night, between 10pm and 6am."

http://www.garden4less.co.uk/watering-the-lawn-at-night.asp

You shouldn't water in the morning because water spots on leaves will cause leaf-burn when the sun gets hot.

I think the best advise, I could give for plants and such like, which works for me, is to water very early in the morning, and only water the roots, thoroughly. Because if you don't water well, the roots come up slightly, and these will burn and get damaged.

If this is grass, I think the maxim is 1 inch a week, as too much water is as bad as not enough. Due to the difficulty of getting the grass leaves to dry out properly, before the sun burns them, the recommendation is to do this at night, leaving plenty of time for it to be sucked up before evaporation takes hold.

As for not watering at night, as the plants would catch rot, mildew, etc. well, in the UK, we have a high dew point where the grass is always wet at night and it, mine, and other lawns, survive. My sprinkler goes on about 9-10pm, FWIW

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    "You shouldn't water in the morning because water spots on leaves will cause leaf-burn when the sun gets hot." This seems not a serious reason based on skeptics.stackexchange.com/questions/2853/… – Suma Jun 3 '11 at 21:06
  • My wife watered my plants on Sat morning. They leaves were fried by the time I got home. I'd mark this one as fact... – Hairy Jun 6 '11 at 6:49

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