How much should the temperature of irrigation water controlled?

organic_wonderfulApril 30, 2011

Right back when I was first getting into gardening and doing research, I was told in no uncertain terms that watering container plants with ice cold water straight from the tap can cause 'shock', for want of a better word, to the plant such as my tomatoes for example. After some questioning, I was told that for plants like tomatoes, the ideal temperature of the water used to water or feed the plants should be about 18-23C, but that mixing cold water from the tap with some boiled water from the kettle (I don't have hot water from the tap in my house) could raise the temperature enough and that subjectively it should feel tepid. I've been using tepid water faithfully ever since, even though it is a pain having to constantly boil kettle after kettle of water to add meticulously to cold water from the tap.

At the garden centre and in other peoples' gardens and allotments, they don't seem to be so concerned with getting the water temperature right, and even use hose pipe sprayers connected straight to the mains, so that cold water comes through when watering the plant. So, I was curious - do I need to be warming up the water each time I water? Does it make a difference at all? If so, is it noticeable?

If I could simplify things I just use the cold water straight from the tap without any problems then it would make my life SO much easier!

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calistoga_al ca 15 usda 9

I try not to use water at extreme temperatures hot or cold. Water standing in my garden hose in the summer can be quite hot, while water in the winter can be quite cold. It is easy to drain off the overheated water and except for house plants, not much water is needed in the winter, and can be allowed to warm to room temperature in the watering can. In the greenhouse watering containers from the bottom, mostly, I keep a container on the heat table, so the water is always close to the temperature of the plants. I have several spray bottles also at 70 degrees on the same table. Except for the new starts and really extreme temperatures I don't worry about it. Al

    Bookmark   April 30, 2011 at 9:02AM
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tapla (mid-MI z5b-6a)

I've always tried to water indoor plants with room temperature water because I remember being told you should. I water from the hose outdoors, so that water is often more than 30* cooler than air temps, and plants don't SEEM to mind, but of course I never see how they WOULD have responded to warmer water. I've wondered about this a lot, but actually can't remember reading anything about it, other than the oft repeated advice that it will shock your plant's system. That's not enough for me, because there are TONS of old wives tales that are perpetually promulgated by people who actually know less than I do about the subject and are also just repeating what they read somewhere.

That said, I just spent an hour looking around the net, trying to come up with something we could sink our teeth into and know we're hanging on to a certainty, but no deal. So far, what I've read greatly conflicts, and the more scientific info I stumbled across seems to lean in the direction of it varying by plant, which sort of means, since we don't know by WHICH plant, that we should avoid watering with hot or cold water if possible.

I'll put this on my list of things to learn more about, and the next time I'm rubbing elbows with someone I think is qualified to answer, I'll share ..... unless someone beats me to it with something definite that covers all plants .... or at least a large %.

I have some texts at home on greenhouse crop mgmt that just might address it, so I'll look later today, after work.


    Bookmark   April 30, 2011 at 10:34AM
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I don't think there is an answer, because unfortunately, plants don't tell us. I always like to look at it as if the plants were growing wild. Odds are, in the wild, plants aren't going to get doused with water that is excessively cold or hot. Granted, growing in containers isn't natural, but we're trying to get close right? With that said, I always water with room temperature water. My rain water is stored in a 55g barrel in the basement, which is cooler then room temperature upstairs, but I always fill a sprinkling pail, and have it tucked in the corner up here. For outside, I just have a full sprinkling pail that I perviously filled up, so after I use it, I fill it again. Do I ever use the hose.....well, sure, in a pinch, but I minimize it as much as possible.

I suppose this could be answered with an experiment. Grow three identical plants, with ALL perameters the same, and water one with cold, one with hot, and one with room temperature water. If there is a difference over time, then you'd be on to something. Of course, you'd have to do it again, or grow more then three plants to rule out coincedence.


    Bookmark   April 30, 2011 at 10:56AM
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greenman28 NorCal 7b/8a

I, too, use room temp water for my indoor plants.
And during the heat of summer, I let the outdoor hose run until the water coming out has cooled.

Something I've considered is that slightly warm water flushes salts more readily, and so I use
warmer water to flush mixes and also to prepare my fertilization water. It seems logical....
though it could be wrong :-)


    Bookmark   April 30, 2011 at 11:31AM
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tapla (mid-MI z5b-6a)

We can say with a great degree of certainty that cold root temperatures inhibit growth. Cold irrigation is used on some plants (like Easter Lily) to help keep the plant short and stocky without affecting the number of bloom heads. So it stands to reason that at least for the length of time the soil is chilled from applications of cold irrigation water, growth would be inhibited, but the question is, 'What happens as the soil temperature equalizes with ambient temps?' I know that many tropical plants, when exposed to chill below about 55* experience inhibition of their photosynthesizing machinery that lasts far longer than the chill - more than a day or two to return to normal in many cases; so what I'm wondering is, what are the longer term subsequent effects to watering with cold water ..... and does it vary (and how much) on a plant by plant basis? I'll try to find out at my next opportunity.


    Bookmark   April 30, 2011 at 8:34PM
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I don't suppose it matters all that much... mainly because the watered soil will cool down anyway, and in winter this can amount to rather chilly for indoor pots... especially the clay ones.

Rain is rather chilly... even in summer... and outdoor plants don't seem at all affected by it.

Personally, I pre-fill my gallon milk jugs with tap water and allow it reach ambient temperature before watering. This gives me an opportunity to add fertilizers, as well. I only do this for my indoor potted plants.

Outdoors, I use water straight from the well, which amounts to cold water. I first allow the hot water in the hose to exit... that happens when the hose is laying in the sun... and when it reaches a temperature I can handle on my skin, I begin watering. The water eventually gets quite cold, coming straight from an underground aquifer to our well's pressure tank, but the plants don't seem to mind very much.

I don't think I've ever noticed an issue from water temperature... unless that water was hot.

    Bookmark   May 1, 2011 at 9:41AM
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Do update us when you find out, tapla, because using a sprayer on a hose would be a lot easier than having to boil my kettle constantly every time I want to water my plants!

I might try and water a couple of plants with cold water to see how much of an effect it has myself, just to see what happens for interest's sake.

    Bookmark   May 3, 2011 at 10:58PM
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zubababy(6b Utah)

I would be very interested in the info that is found on this as well.

I've watered the plants in my greenhouse with the hose during the winter, with very cold water - when the weather is barely warm enough to turn my sprinkler system on and not freeze. When the weather is too cold to turn the system on, I use a large garbage can that is filled with water - also very cold, but not as cold as the hose.

I have watered my plants this way for a few years now. I also water my seedlings this way. Probably not ideal, but it's what I have to work with.

I haven't had any plants die from it (or I haven't been able to pin it on the water), but maybe they aren't performing their best because if it? Oh wait, that's likely because I'm not as good as I should be with the fertilizer. :)

    Bookmark   May 4, 2011 at 1:01AM
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Well... it's a known fact that the hotter the water, the faster it freezes in cold weather/freezing conditions. So I don't think it would be to our plants' advantage to warm the water beforehand in any weather, but especially not in winter.

In nature, at least in my climate, the rain never seems to be what I would call "warm". It's always on the chilly side. Plants in nature don't seem to mind this one bit.

I think it's probably best to use water of an ambient temperature... water having been drawn from the tap or well and allowed to sit for a bit... but I don't think there's really any disadvantage to using water that's a bit colder. I would think a disadvantage only exists in warmer water than ambient temperatures.

    Bookmark   May 4, 2011 at 9:51AM
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tapla (mid-MI z5b-6a)

We do know that growth slows considerably at soil temps below 55*. so the main questions are how long does the effect of the chilled soil last, and are roots actually 'shocked' by applications of hot or cold water, and by what standards to we measure hot and cold? If the soil temp is 40* and we apply 80* water, is that (relatively speaking) 'hot' and does it shock plants - for how long? Conversely, if ambient temps are 100* and we apply cold water from the hose (60*), what does it do to the roots (physiologically) and for how long?

Sudden chill can cause plants to shed foliage, even if temps are nowhere near freezing, and foliage damage (chill injury) can occur in many plants at as high as 45-50* if the temperature drops fast enough because of phenolic compounds that leak from leaf cells. It really wouldn't be much of a leap to imaging that the same process MIGHT occur in root issues subjected to sudden chill via a frigid bath.

I sort of forgot about this question, but I'll ask around. I have some events coming up in May where I'll be rubbing elbows with some people positioned pretty highly in the horticultural hierarchy.


    Bookmark   May 4, 2011 at 10:12AM
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Has anyone gained any insight on this topic over the past year?

I'm trying to figure out how to set things up for the season and would like to move many of the containers off of the deck and out to the edge of the yard. The containers are multiplying so rapidly that space on the deck is becoming limited. Last year the routine was to add the fertilizer concentrate to the watering can, fill it inside with tepid water, carry it out to the deck and water, then repeat as needed until all the plants are happy. The new location will be on the other side of the yard, which is too far to keep running back to the house to fill the 2 gal. watering can. I'm considering getting an EZ-Flo fertilizer injector which feeds into the hose bib. Then 150 ft. of hose (I still have to measure that to make sure) and a watering wand should do the trick (can anyone recommend a good watering wand?). The plants are primarily conifers, maples, and chile peppers, and my concern is the water temp. As others have noted , water from the hose bib is cold even in the summer - will this have implications on the plants' vitality? I'm especially concerned for the peppers.

Plan B is to get a reservoir (probably a garbage can, but it could be a rain barrel), install a hose bib near the bottom, and place this in a shaded location near the plants. I envision sitting the reservoir on a table for ease of accessibility. I might have to fill a watering can, I don't know if it would generate the pressure to use a watering wand. Fill the reservoir with water and in a day or so I'll have a source of water at ambient temperature. Ideally, one could add fertilizer concentrate to the can, but in practice though, the can doesn't have a tight lid, and evaporation will result in concentration of the contents. On the other hand, there's an adapter you can get for the fertilizer injector to allow it to function in low flow applications (think drip), and that might be applicable. Plan B requires somewhat more work, but does not have the cold water liability. Also, what with the reservoir up on a table, I wonder what will happen when that big storm rolls through.

I'll make a decision soon so I that can buy what I need. I'd be really interested in any additional info on use of cold water in the summer. Also, I'd love any feedback on Plan A or Plan B, or any other alternatives.


    Bookmark   March 14, 2012 at 4:23PM
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