I was always told not to water veggies during the heat of the day because it is said to sunburn them or otherwise shock them. And I guess that’s so. But it’s not always possible, or at least convenient, to wait.
So what are useful guidelines? Right now it’s 80F here at 6 pm and I’d like to get some water on my lettuce, peas, kale and tomatoes/ It’s still sunny, though the sun is lower in the sky and not so direct.
Its a myth. Water whenever you think your plants need it.
It can happen but it’s rare and minor. It’s more about the strength of the sunlight than the temp. Realistically, you can water whenever, but if given a choice, avoid the middle of the day. You also lose more of your water to evaporation, too. Then there’s the whole morning vs. afternoon debate…
I thought that it was still wintertime in the frozen tundra of Montana. 
no thats northern maine. i lost my last snowbank about 12 days ago.
I’ve had big damage from watering mid day in the middle of summer. Leaves all shriveled brown and crispy. 
I think 6pm is fine though, in my limited experience it’s been when I watered between 12-2 that it damaged plants
Golf courses use a technique called “syringing” on greens where they apply just enough water from overhead to wet the blades. It cools the grass when the water evaporates and relieves heat stress. It works best when humidity is low and there is some wind.
For plants like lettuce, the soil can still be moist but they will still wilt if too hot, but some quick overhead water can bring them back. If it is muggy and calm, I turn on the drip, even though the plants don’t “need” water, that water is like 60 degrees and will help relieve stress. I’m growing on raised beds, so never really had a problem with rotting roots. Of course you don’t want to apply scalding hot water, so let the hose run out first.
I just wonder who wants to go out in the midday of summer. Today is 93F, I feel like my skin is sizzling.
Growing aint easy, when the power goes out I’ve got to get into a 120 degree plus greenhouse and keep hosing everything down or else it is toast!
Here you are forced to water during the heat of the day in the most intense of summer if you want things in pots to stay alive. They can be soaked at 8am and dessicated by 1pm. Larger pots help but are heavy. I also will hose down a plant lightly when its crazy hot, i do not think the water drops are good since they are magnifying the sun but with 0% humidity when you blink the waters gone. I would also do this for my in ground garden but not near as needy as raised beds or pots.
I would bet the people that get burn damage from watering during the day get it because there is 100°F+ water that is still in their hose.
Nobody worries when there is a sun shower during a hot day. Nor do farmers that use automated overhead irrigation. Nor do garden centers when they water all their plants.
This is a excellent point @dimitri_7a When you go to vegas with all those mirrored buildings on the strip they have misters all over for the plants (definitely people mainly) and everywhere you see them misting the plants they are much happier. I was wondering how they stayed alive with all that reflected heat light and dessicating wind and wondered if most of these were all nursery grown and just replaced every week/month etc…
I have often heard people say to not water during the heat of day…
But I personally have not noticed any ill effects .
And have watered a lot on hot days.
I think it’s good to let the leafs dry befor dark, to reduce leaf / fruit rots.
If that hot, you should move to half shade place if you can move, or install a mist system controlled by timer.
It is very easy to install. I also found the people installed the shade cloth above the plants.
Under that heat, the sun possibly burns me instead of the plants.
I grow plants for hobby, not devote my life to plants.
@Sophia2017 I agree i also hate being a slave to the plants, My tomatoes in 20 gallon fabric pots in only morning light still would be dry by noon and my tomatoes in 30 gallons in full sun were in a similar situation. I used terra cotta and wine bottles full of water to keep them alive until evening. Which still makes them need water daily but since my dogs are not camels i do these things anyways. The change to the raised beds has been nice and once i am not trying to start seeds in a early summer will be easy to put on a irrigation system.
The last week has been brutal with very rough heat and a oppressive sun, I need my afternoon showers!
It depends (haha you knew it was coming). I grow only greens and roots these days, and those can take water anytime in the day. They are not tomatoes, and anyway tomatoes should not be watered from above at any time. Plus, I have a few scattered empty patches, which I seeded mostly with chicory, and those seeds want some heat before coming out but do not want too hot soil. I need to keep it cool until they emerge, and so I water. If you also grow fruiting vegetables, it pays to plan ahead so you can irrigate from below one patch, and water from above another.
Where you live is important too. Here in PA watering should have a chance to dry as molds and fungi are lurking around every moist evening
I used grass clippings and covered the base of all my pots like figs, tomatoes, and peppers. The 5 inches packed layer of grass clippings will prevent water evaporation from the hot sun and keep my potted plants alive until I watered them around 8pm after dinner. This will also give a slow release of Nitrogen from the breaking down of the grass clippings. There you go! Done this for the last 8 years.
It’s true, there is no springtime (or fall weather) here in Montana. It goes from winter to summer and back a few times, before finally arriving at summer. A couple days from now, we are having high temps in the 50’s and I’ll probably be wearing my thermals again before finally putting them away until the beginning of September.
Here is a scientific study that addresses this: https://www.sciencedaily.com/releases/2010/01/100111091226.htm