One popular myth about houseplants is that you have let tap water rest for 24 hours before use to prevent damages caused by the chlorine it contains. But this is a waste of time for two reasons.
First, there is not enough chlorine in tap water to affect most plants. Water from the tap, preferably tepid water, suits them perfectly. That’s good, too, because with some 300 indoor plants to water, I would have to leave at least 75 watering cans out the day before watering! It is also worth noting that chlorine is one of the minor elements that plants require for good growth. So they actually need a small amount of chlorine.
Secondly, letting tap water sit overnight will not necessarily reduce the quantity of chlorine it contains. That’s because many municipalities now use chloramine (a compound containing chlorine) rather then volatile chlorine to treat their water. Chloramine, unlike chlorine, does not evaporate when you let water sit out, at least, not to many great degree. That’s why municipalities use it: its antimicrobial effect is much more durable than that of volatile chlorine.
In fact, letting the water sit out will often concentrate the level of chloramine in the water … although only very slightly.
Problem solved, right? Not so fast!
Extra-Sensitive Plants
OK, letting water sit overnight doesn’t allow chloramine to evaporate, but still, some plants are sensitive to the chlorine compounds in tap water, including chloramine. This includes dracaenas (Dracaena), ti plants (Cordyline), spider plants (Chlorophytum comosum), prayer plants (Maranta), calatheas (Calathea) and carnivorous plants. If these plants are watered with heavily chlorinated water, it can cause the tips of the leaves to die and turn black. What can you go about that?
It’s important to note, though, that chlorinated water is only one of the causes of black leaf tips: dry air, drought stress, and excess fertilizer also “burn” the leaves of these plants, and in fact damage due to chlorinated water is a fairly minor factor. So you can’t just blame the tap water…
In an ideal world, you wouldn’t water these plants with tap water at all, but instead use rainwater or distilled water. That would solve the chloramine problem, but rainwater can be hard to come by and is often inconvenient, while distilled water is expensive. Again, letting the water sit overnight is of no help whatsoever.
The Easy Way Out
Here’s what I do: I water plants subject to black tips (except carnivorous plants, which aren’t “regular houseplants” and need special care in so many ways that you really have to treat them separately anyway) with regular tap water along with all my other houseplants and have learned to just put up with the occasional blackened leaf tip. I’ve also learned that if I keep the air fairly humid, leach these plants occasionally to remove excess mineral salts in their potting mix, and don’t stress them with underwatering, there is very little leaf tip damage anyway. Only the very tippy tip of some leaves dies back a bit.
Essentially, I just apply the Laidback Gardener’s “15 Pace Rule.” Back up 15 steps and if you can’t see the problem, it’s not one worth getting upset about. That’s certainly the case here!
Letting the chlorine evaporate isn’t as much for the plants as it is for the microbes in the soil, which you probably don’t have a ton of anyways considering you’re using mineral based salt nutrients. There’s water filters you can buy that a lot of people use for gardening that filter out chlorine too
This is a misleading article – misleading in that it ignores certain important facts. While chlorine won’t ‘hurt’ plants (arguably subjective as it will leave them potentially malnutritioned) it will curtail them from reaching their potential and / or slow them from reaching their potential. There is a symbiotic relationship between plants via their roots with any number of bacteria – the ‘rhizosphere’. The bacteria make nutrients more bioavailable to plants. Chlorine kills these bacterial which in turn makes the plant less able to uptake nutrients and / or causes stress. So while the plant maybe ok it will not be as healthy, or large or yield as much as genetically possible as each watering kills the microorganisms that assist it. So important is the rhizosphere that plants often build it up. So yes steps should definitely be taken to ensure that all chemicals that can destroy the rhizosphere are removed if you want to be a great gardener and not just a good enough gardener. Also letting water with chloramine sit where it will received UV light (eg. outside, near a window) will via photodegradation / photolysis see the chloramine neutralised, a small misleading fact also glossed over in the article. If you’re going to position yourself as an expert it is probably best to understand and explain the whole picture and not ignore the inconvenient parts that don’t support your assertion. A tank with a hose will allow for water to sit and negate any need for a watering can.
https://asm.org/Articles/2018/April/plants-and-the-bacteria-at-the-root-of-it-all#:~:text=Bacteria%20benefit%20from%20the%20plant,variety%20of%20growth%2Dpromoting%20functions.
https://link.springer.com/article/10.1007/s11104-007-9514-z
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/rhizosphere
I loved this article and I am thankful to other experts who add to the information by their comments. Your added contribution is priceless! I’ve found that sometimes I learn more from the comments than I do from the article! But usually the article is the catalyst and has tons of information and the comments definitely adds important, sometimes vital knowledge to what the article is providing. Seriously, priceless!!! Thank you so much!!! Yet another benefit of connectivity and the internet! Collective wisdom unleashed!!!
Dear LBG,
I have an all-container garden with indoor and outdoor plants. In the second to last paragraph, you stated “…leach these plants occasionally to remove excess mineral salts in their potting mix…”
Can you tell me more about this process? When might I need to do this? Thank you!
https://laidbackgardener.blog/2019/02/24/how-to-leach-a-houseplant-no-leeches-required/
If it’s a big issue (and in some places it might be, don’t just assume the same concentration of chlorine is used everywhere in the world), you can always just mix in some ascorbic acid (synthetic vitamin C) powder and it will quickly neutralize both chlorine and chloramine.
At any rate, it really won’t hurt the plant to any degree.
Vitamin C will “neutralise” chlorine? What does that mean?
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This does not appear true to me. Test it yourself. Buy a PH kit.
Pour some water from your tap. Test it. Then let it sit over night. Test it again.
Make your own decision.
The pH of water is determined by a number of factors, of which chlorine is only one and often a minor one. I don’t see how this applies.
he probably meant to reply to donjoe0
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