I was planting some 'maters (cue pseudo-Samwise: “Toe-MAY-toes!”) the other evening and, when it came time to water them I remembered the days of my youth – oh, so long ago – and the sage advice of my father never to water plants in the middle of a hot day because it might “burn them up.” It being evening at the time, it didn’t really matter, but it did get me curious as to whether there was any truth to that old piece of wisdom.
Anyone out there knowledgeable on this subject?
(In all fairness to my dad, I may well have conflated this concept with that of being careful not to over-fertilize the plants.)
Thanks,
RR
The idea of watering early in the morning or in the evening is that it’ll count for more. If you water in the heat of the day a lot of it will evaporate rather than actually getting into the plant. I’ve never heard anyone use the phrase “burn them up” with watering plants, just over-fertilizing.
I have heard the theory that if you water a plant during the day it will react as though it were raining and open the parts of its leaves that let in water. If the watering time is too short on a hot day this could lead to the openings letting more water out than was taken in. I have no idea if this is true, but that was the reason given. Tomato plants should be watered at the roots, so this would not apply anyway.
Water drops on leaves in intense light may burn the leaves at the point of focus is what burning up means in your situation. You’ll have to test it yourself.
This is what would normally be referred to as burn them up. Applying water soluble fertilizer or other sprays can burn the leaves. This is more likely closer to high noon under an intense sunlight and higher temperatures.
Yes, aside from wasting water because most of the water simply evaporates, the droplets act like lenses that concentrate sunlight and can cause damage.
As proof, I point to various experts that say that in dry summers, forest fires have started from dew drops acting like focal lenses for sunlight.
Also, if you look at nature, aside from tropical rain forests, it’s natural for the plants to get water in the morning/evening (dew) or during rain (when the sun is hidden by clouds). It doesn’t often “rain” = watering can while the sun is shining brightly at noon in temperate climate.
I don’t have my own garden, and I wouldn’t want to burn my plants on purpose just to prove something.
These experts are the guys on TV who explain how a forest fire got started. Some of them are firemen, so probably fire investigators. I remember this because in the 80s, in dry summers, they were warning us not only about smoldering cigarette butts, but also about broken glass acting like lenses; and then later, they said that many fires started without any of these (or arson), but by natural causes. And if there hasn’t been a thunderstorm, you can rule out lighting strike, too.
My dad had two reasons for not watering tomatoes until evening - the waste of water due to evaporation and the droplets on the leaves burning them, just as others have said upthread.
He also used rain water only to irrigate tomatoes. If the rain barrel was totally out and he only had tap water, he would fill the rain barrel in the morning so that by watering time, the chlorine (and anything else in the tap water) would have had a chance to evaporate out.
My experience is different than the average gardener, in that I water—Lord, do I ever water— plants in small pots in a nursery. In the Hot Months here in the South, I have to water in the afternoon, and, have never observed any hot spots from water droplets damaging the plants, honest. Before I had this job, I believed that, too. But, I am watering with a hose wand at the root base, and not overhead sprinkler watering. Still, some water hits the leaves, and, have never seen leaf burn, from eight years of, did I say a whole lot of dang watering?
That said, it’s best to water plants in the morning simply because they are then more able to deal with the PM heat when fully hydrated, especially here in the hot South.
The forest fire ignition seems very far-fetched, would like to hear some proof behind that.
For lwns they recommend NOT watering in the evening; the plants stay damp & that promotes fungus & rot.
I suspect that’s not as much of an issue with a plant with its leaves more separated and above ground, like 'maters. But it’s dtill sounds advice.
The ideas that droplets are lenses which could concentrate the Sun on leaves is bogus. The physics don’t work that way. That’s pure ignorance disguised as “common sense.”
If I remember my plant biology correctly, most plants have many stoma (sp?), aka orifices that they use to collect water. Most plant life is dormant during the night. All orifices are closed during the night to protect against freezing. When the sun comes up, the plant wakes up and the light triggers their chlorophyll jones, these thingies open. They collect water. They collect sunlight to their (non-literal) heart’s content, until they’re full. After some time, each plant decides that they’ve had their fill and shut the openings. Possibly to protect against heat and other pollenation damages. Then they sauce the ragu that is the water+CO2+chlorophyll mix in their little plant Easy Bake Ovens…
Product? OXYGEN!
The response from the plants: Water us at the wrong time, bub, and we’ll take over your lawn.
Sorry. The whole point of that post was that if you water the plant in the middle of the day, you confuse them. Plants close these openings when they’ve put enough food in their ovens gathered from the sunlight and early morning dew (Full Metal Jacket reference not included). When you water them later in the day, the plants reflexively open their stoma (again with the nouns) and allow not only the extra water but also the additional energy from more sunlight than they want trigger the photosynthesis reaction and it freaks out their Easy-Bake-Plant ovens and does something catastrophic to the plant metabolism. Think about pouring gasoline on a fire, in terms of plant biology.
This is what kills them. What the evil sun voodoo noontime water combo does, I do not remember.
Kill me. I am not a botanist.
Apologies for the whacked posting… I got distracted by Metallica on Discovery Channel.
Plants have small openings on their leaves called stomata. They are not for the purpose of taking in water, but for taking in carbon dioxide to use in photosynthesis. They lose water vapor through the stomata when they are open.
With all due respect, Uncle Brother Walker, your posts are so full of mistakes and misinformation about plant physiology that I am not sure exactly where to begin in correcting them.
Not meaning to be rude, but I did say “IF I remember…”, as well as corrected myself on the misremembering of the actual noun.
and besides, Metallica was on… so call me whatever you want.
I’m a metalhead. I call myself that (no abuse involved, mods). I like being a metalhead. We’re not all as stupid as I am.
Would you care to elaborate upon the actual process of photosynthesis?
P.S. There is a lot of self-censoring going on, but this is not the pit, eh? And this is not a fight. I’ll just say I was wrong. But I do think I’m on the right track somewhere? If not, let’s forget about it.
I’ll just say that, this being GQ, it’s good to take some care in making sure what you post is correct, rather than just posting stuff off the top of your head.
Well, I could, but it’s late and I’m going to bed.
Some of what you posted is correct. Some of what you posted is bizarre (such as saying that the stomata “collect sunlight”). Like I said, I’m not sure how exactly to go about sorting the wheat from the chaff.
I’m curious as to how a water drop would concentrate enough light to burn leaves given there’s no distance between the water/leaf interface for a focal point to reside.
To be clear burning the leaves means to kill the plant cells, and not actually starting a tiny fire. The phrase you will cook the plants is more accurate for the watering during intense light claim. Somebody else will have to prove it true as I’ve near achieved this. I’ve only believed somebody is telling a tale they think is true. I’ve only killed leaves with spraying fertilizer or insecticides in too hot of weather. Ive also sunburned plants to death by too much intense sun.
Maybe it occurs for people with too much chlorine in the water supply or lots of lime and other minerals.
In the summer we will get quick flash sprinkles that sometimes last only a minute or two before the sun is back out and I’ve never seen any damaged plants or crops after this happens. I have some container herbs that have a tough time in the summer heat and are often looking a bit wilted by mid afternoon. When this happens I’ll give them some water and they perk right up. This is the middle of Texas so the heat and the sunlight are fairly intense.
I have seen labels warning on some plant products (tomato blossom end rot spray comes to mind, along with some insecticidal soap) that say you shouldn’t use them when the sun is out, but I’ve never had or seen a problem with plain water.
Here’s some stuff I found on Google that backs up my own experience with midday watering.
