Comment by monopoledance | Hacker News Reader

Comment by monopoledance | Hacker News Reader

Tl;dr: Lots of houseplants die. The end.

Anyway, since you are here: You may kill your plants with tap water. Plants evolved to get demineralized rainwater. The salts of tap water will build up in the soil, slowly poisoning the plant. Additionally the pot is also the plant’s potty: It disposes excess minerals and waste through the roots, and expects the rain to flush it away.

It’s best to water your plants with demineralized water, but you can also use (old) boiled and cooled down water, which lost at least some CO2 and consequently fell out calcium. In any case, if you water your plant, do so thoroughly, until water comes out at the bottom. Let it collect for a few minutes and then dispose it. Do not let it reabsorb! This will help the plant getting rid of salts and also helps not getting the soil soaking wet.

Btw. this is also why irrigation is a problem for food security. Using straight underground water for crops in hot regions will only work for a few years, until the soil is dead for good….

Edit: Oh yeah, and IIRC the snake plants leaf tips are crucial for growth. They may be hurt from handling in the store and will consequently not grow in length anymore. Not sure it has anything to do with watering at all. My snake plant got “store leaves”, which haven’t changed at all over the years, got brown just at the very end, and new leaves, which are almost double the length and totally healthy. Maybe a brown tip is just the normal display of a leaf without a head (cell).

Fun fact: Did you know snake plants store “sun energy” at daylight, and then do the rest of photosynthesis at night? So they do not lose water due to evaporation as much, when opening their pores for gas exchange! Pretty cool, eh?!

Yes, cool, didn’t know. Reminds me of how some plants move water from deep in the soil up the roots at night — to hydrate the soil around the dry roots near ground level for when the day comes

Does leaving tap water out help with the salt problem? I've read that after 4 days, most of the chlorine will evaporate from tap water - and this is good for plants.

No, the salts don't evaporate. Which is why they tend to accumulate in the soil.

Hypochlorite (like they add for disinfection) will break down on standing, or faster with aeration. Chloramine (also added for disinfection) won't, which is why aquarists use various chemical treatments to remove that.

Neither is too important for plants, though. The usual problem for plants is chloride, which can't be removed except by processes like reverse osmosis or distillation. Most plants can easily survive chloride at typical concentrations in tap water; but if you don't water to runoff then that concentration may slowly increase in the root zone, eventually harming the plant. You typically want something around 10% runoff, though that will vary with your plant species, water, fertilizer, etc.

Others have answered the question already, but I want to extent on my comment: Long standing water, same as boiled water loses some CO2. CO2 in water forms carbonic acid in part, which dissolves calcium salts. Removing the acid, will make some of the calcium salts insoluble (that’s why you get a buildup in water boilers). Most other salts are unaffected by that. So the disposal of collected water under the pot is without an alternative. Even if you’re using demineralized water, you need to flush the plant’s toilet.

Doesn't that also flush out any fertilizers added to the soil?

Yes, but that's a good thing. You are much more likely to burn your plant with fertilizer, than starving it. If you think about the typical environment most plants adapted to, you will not have a year's worth of N2, P, ... supplied once a year, but a constant, very low exposure through rain and continuous organic decay/production processes in the soil and above. For the most part, plants rely on osmosis, the capillary effect and evaporation to transport nutrients. Salt levels, including fertilizer, modify the osmotic costs and limits.

tap water

Foreign speaker here. Thanks, fixed.

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