I've read the part about roots several times and don't understand it. Is there some intermediate level of actionable advice between "water once a week" and this? If anyone can explain it to me in a way that makes sense to a programmer it would be much appreciated. I do have multi-year surviving house plants but worry about their roots.
> This comes about by having the roots well distributed in free-draining soil so that water and oxygen can feed the plant. From this you can infer there might be a problem If water runs right through the pot, and/or you squeeze the pot at its base and it’s rock solid. If so, take the pot off and have a look. From this you can also infer that, repotting into a much larger pot will just leave the roots buried in a mound of cold, wet soil, far from any roots. You might also see that a root-bound plant might not even need to be repotted, or can be repotted back into the same pot.
I also found that advice about as confusing as all the other consumer-targeted houseplant advice. If you've got some time to invest, then I believe you'll find that advice for professional growers makes a lot more sense, much more quantitative and backed by trials and chemical or biological mechanisms. I quite like:
That's a guide to operating a nursery, developed by academics seeking to distill the scientific state of the art into something practically useful with basic equipment.
Specifically as to judging how much to water, I go mostly by weight. Thoroughly wet the medium until water runs from the holes in the pot, and then don't water again until the weight drops below some fraction (e.g., 20%) of that maximum. You can use a scale, or judge by hand with practice.
You can also wait until the plants show drought stress. For example, they might visibly wilt, or succulent leaves and herbaceous stems may go from turgid to limp. That's probably not optimal, but it's better than overwatering.
Finally, you can also pot in media with very low water holding capacity, like a blend of normal potting mix and perlite. This makes it near-impossible to overwater, but the tradeoff is that frequent (e.g., every few days) watering then becomes mandatory.
Honestly don't worry about it. If your plants are growing and seem healthy, they are fine. Just ensure your plants have a pot that is appropriate to their size. Off the top of my head and based on my current plants, I'd say a plant that's 1 to 2 feet tall needs a pot around 6 inches in diameter and maybe 8 inches tall. 2 to 3 feet, 10 inches and similar height. 4 to 5 feet, 12 inches and 12 to 16 inches tall. Past that, and you don't need any advice on plants.
For many indoor plants, soil acts as a porous environment for roots to hang out in, where there’s humidity and air. Too much soil act as nothing but a wet blanket, too root-bound and the roots are not held in soil at all, so are poorly fed. Water only to rehydrate the soil, not to keep roots chronically wet
> This comes about by having the roots well distributed in free-draining soil so that water and oxygen can feed the plant. From this you can infer there might be a problem If water runs right through the pot, and/or you squeeze the pot at its base and it’s rock solid. If so, take the pot off and have a look. From this you can also infer that, repotting into a much larger pot will just leave the roots buried in a mound of cold, wet soil, far from any roots. You might also see that a root-bound plant might not even need to be repotted, or can be repotted back into the same pot.