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Does Water Temperature Matter? Does the Type of Water?


Peter Henderson’s 1874 gardening book, Practical Floriculture, is an idea-provoking read that leaves me wondering where he got his manic amounts of energy. One of the things he seemed to enjoy most was experimenting with new technologies, and pooh-poohing old superstions.

One piece of dogma he refutes is the notion of using only soft water or rain water for plants, very popular then, and still recommended now. This is problematic for those of us whose water is full of minerals, and whose rain is only available for part of the year.  The other dictum about watering that Henderson refutes, is that most plants prefer warm water (bulbs don’t; they’re late-winter/early-spring creatures, adapted to cold).

Fortunately for a lot of us, Henderson dispels both these myths. He describes a greenhouse in Jersey City where he grew plants with cold, hard well water, and a greenhouse in Bergen (also in New Jersey) where he gave plants rainwater captured from the roof and stored in cisterns. “…yet we have never been able to see that our plants have been any better grown or healthier in one place than another.”

I will say from my own observation that rainwater (from the sky, as nature provides it) does seem to me to make plants grow more lushly and greenly. It could be because of nitrogen in the water, or it could just be that the time of year it rains here is the time when things are cool and moist and much more likely to be lush.

Whether municipal water poses more of a problem would be harder to say. In 1874, they didn’t use chlorine in their water supply, and there were plusses and minuses to that. Chlorine is used because it’s toxic to every form of organic life. Since people recommend that you let water sit and evaporate chlorine before filling a fish tank, it’s probably not all that great for plants either (or us), but then neither are typhoid fever and all the other great things you get from water gone bad.

As for the temperature of the water, Henderson explains, a simple thermometer test combined with observation takes care of that. He measured his greenhouse soil at 80 degrees; theory had it that the water was supposed to be the same temperature. Henderson begs to differ. “If we pour a pint of water at 40 degrees [about 4.4 degrees C] into the soil, the temperature will not be 40 degrees, but above the mean between 40 and 80 degrees [about 27 degrees C], or about 60 degrees [around 15.5 degrees C]. Now if the soil remained for any length of time at 60 degrees, it might be claimed to be injurious, but it does not.” In ten minutes, the soil temperature is back to normal, or almost.

“It is the duration of extremes of temperature that does the mischief; place a plant of Coleus in a temperature of 33 degrees (just above freezing in Fahrenheit) for 24 hours, and it will be almost certain to die, while it would remain as many minutes without injury. Let a dash of sun raise the temperature of your hot-bed to 100 degrees [ 38C], or over, for 10 minutes, and it will not seriously injure the contents, but an hour of this temperature might destroy the whole.”

He likens this to drinking ice water; the temperature is radically different from our body’s,  but most stomachs are up to the task of bringing the water up to body temperature pretty quickly, so even though having our insides at ice-temperatures is dangerous, it would take a heck of a lot of ice water for that to happen.

So for those who worry about such esoterica: worry no longer. And for those who are worried by people who worry about such esoterica: you’ve now got the perfect answer. Science and history have proven it: we can retire from excessive water snobbery, and all that heating and storing of water that I’m sure somebody did. Me, I’m just glad that science and history are providing a rationalization for sloth.

{ 13 comments… add one }

  • Steve July 23, 2009, 5:55 pm

    Those daggone Water Snobs, anyway! I got a laugh from that part of your post, Pomona. I have found…….to repeat your earlier claim – that rainwater is the most nutritious of all – demonstrably so. This is undoubtedly owing to all the junk in our water treatments prior to their trip out the cisterns.

  • Nancy Bond July 23, 2009, 7:44 pm

    Very interesting, Pomona. I do agree with you on the rain vs. tap/well water theory…I do believe rain produces much lusher plants. Or perhaps it is just that the rain waters more efficiently. 😉

  • Monica the Garden Faerie July 24, 2009, 5:09 am

    I love my rain barrels but I also water using a hose. For indoor plants I heard cold water is better; I don’t recall why. I don’t have a greenhouse, so the rest takes care if itself!

  • Sylvia (England) July 24, 2009, 6:09 am

    Pomona, this is very interesting because these things are written time and time again. I am sure that rain water is better for ericaceous plants but no water is a lot worse than using alkaline tap water! I do think my seedlings would prefer not to be watered in very cold water but they usually survive.

    Best wishes Sylvia (England)

  • Naomi Sachs July 26, 2009, 11:03 am

    What an interesting post! I’ve often wondered about this. Thanks for providing such good info!

  • Mosaic Queen July 27, 2009, 9:05 am

    I read that rain water is better for our plants as it is full of oxygen and our tap water is not. This is why the plants seem to perk up and green up when it rains. It’s the fresh oxygen :-)

  • Cyd July 27, 2009, 12:21 pm

    I’m all for sloth in some things! I do water my African Violets with very warm water, as I’ve heard they enjoy this. They have not complained so far. I have a well and our water tastes really good. There are a lot of calcium deposits from it though. I’m happy when the rain waters for me. I really enjoyed this post because I will take your advice and never worry again!

  • Pomona Belvedere July 27, 2009, 2:44 pm

    I’m interested to hear the spectrum of comments from all of you, especially the feedback on rainwater. I’d love to hear about a contemporary study on this (not that water and plants change much in 135 years, but it would be interesting).

  • wayne July 30, 2009, 11:11 am

    my thoughts on water… in my classroom I have several gallon jugs which we fill with tap water and let sit before we use them on our indoor plants. I once mentioned rain water being better to someone and their take was that rain gives a good drenching unlike many human watering practices. yes, let us have some studies.

  • lostlandscape(James) July 30, 2009, 6:42 pm

    I’d love to be able to use rainwater for everything. Currently the only plants that get pure rainwater are the plants that get no supplemental watering during the 8-9 months of the year when it doesn’t rain here. I used to fuss about water quality for my orchids in years past, but ended up giving them what the tap offered. I’m sure it did in a number of plants, but many did just fine. Your post get me thinking about trying to separate the useful generalizations from the harmful overgeneralizations.

  • Vachtra August 2, 2009, 8:16 pm

    I don’t mean to be contrary, I just am.
    Both the type of water and the temperature matter when watering, depending on the result you are trying to achieve.
    I have written a few times about watering with ice which does very well for the cold adapt plants you don’t want bolting right away.
    As for the type of water, especially plants that aren’t native, you need to make sure they can withstand the chemicals in the water, not just hard or soft but chlorine, flouride, antidepressants.

  • Pomona Belvedere August 4, 2009, 12:03 am

    Debate is always a good thing, it tends to bring up more information!

  • mmmmmmmmmmmmmmas November 6, 2014, 12:04 pm

    plants need cold rainwater

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