Cats peeing in potted plants. What to do?

I think best thing to do would be making these plant pots unattractive as alternatives to litter box.

First thing to consider is replacing the old soil in all these pots, because cats will be attracted to urinate there as long as the soil has cat urine scent to it. I would advise against attempting to dilute the scent by doing washing-overwatering, as you could seriously damage your plants (I've drowned a few potted plants in the past by accident and it's easier than it seems). Next, you could cover up the soil in your pots with some larger rocks, or generally just a layer of some harmless blocky objects - it would impede with cat's natural instinct of covering up urinated places with soil and further discourage using pots as litterboxes.

Some research on the Internet I did also mentions placing rustling materials like aluminium foil ribbons into the pot to further spark a sense of unfamiliar environment being present and thus sending cats a subtle message that flower pots aren't really the best places to urinate into. I don't think it's a bad idea, but if you decide to take that advice please make sure these objects aren't in any way capable of hurting the cats or pose a choking hazard. Due to the latter, I would advise against using for example plastic bag ribbons in this context.

I would also not advise sprinkling cats with water if you see them urinating there, as they wouldn't get the message that urinating is prohibited there. At most, they would learn that it's just you who doesn't like them urinating there. Intended effect would not be achieved, as they will just begin behaving more sneaky and careful about it, causing unneeded stress for them as well as for you.

Also, please rule out that urinating outside of the litterbox is not caused by other factors. For example, I recall an issue someone had with their cat urinating in disagreeable places, and then it was discovered that the reason lied within the litterbox itself, as the texture of recently changed brand of litter was hurting cat's paws.