A chance comment I made in my post on Calatheas 2 weeks ago has led to this post.
One of my faithful commenters pointed out that my watering practices could lead some of you astray because watering from the bottom could lead to toxins from the water accumulating in the soil. He has a valid point.
It’s not that I so much worry about soil “toxins” per se–I think what he was getting at is the build-up of excess salts and minerals that accumulate when you (or I, in this case) exclusively water a plant only from the bottom. I think most of you probably know what this looks like or have seen it somewhere. It looks like a white, crusty ring on the edge of your pot, or white, crusty deposits on tops of the plant soil. Here is an example–although a minor one–of some of that mineral deposit.
It is not perlite, which is a soil additive that loosens soil. This is what perlite looks like.
Normally, setting a plant outside will flush all the mineral deposits from tap water from the soil because it will be watered naturally (and in my case, quite abundantly this summer) by rainwater. You can also avoid this by watering with collected rainwater, if that’s practical for you. If you have a large collection of plants, clearly, that’s not practical.
Over-fertilization with synthetic fertilizers can also cause this problem. Again, flushing the soil–in that case, even with tap water, can be helpful.
And of course, upon re-potting, scraping the pot rim to remove the build-up of deposits is always recommended.
In the case of the Jade plant–the plant I showed with the deposits of minerals–that plant is watered very lightly and not from the bottom. That just shows that any plant that stays in its pot for some time can be prone to this issue.
Unfortunately, most houseplants are tropical specie that are innately sensitive to such toxic mineral deposits. That is one of the two main reasons that those old self watering pots needed distilled water. (The other reason is that the mineral deposits clogged interfered with the operation of the system.)
This is such an important topic and it’s one that no one talks about. People may talk about house plants as tropicals, but they never discuss how or why watering impacts them. About the only thing that ever gets said is that you’re more likely to kill a plant by over watering than by under watering. And while that may be true, clearly there’s lots more to discuss!