Greetings,

I am looking at re-potting several cacti that I have as houseplants. My question is, I have up until now used regular potting soil for them, but I am now looking at using cactus potting soil, like Black Gold.

My question is, can I re pot the cacti into cactus potting mix given that they already have a large amount of their root systems in regular potting soil? If so, should I mix the cactus potting soil in anyway to match/offset the regular potting soil?

Ideally it would be better if I could've just started using cactus potting soil, but at this point, I figure there's no way to remove the regular potting soil from the roots without severe harm to the plants themselves, unless someone has advice on that too.

You can wash the roots of the plants and leave the plant (completely naked, unpotted) for several days to completely dry off. I know several people who do that (some who read this forum) but I've always been too afraid. But you can remove the vast majority of old soil this way.

I would not use a pre-made mix for cacti. All of them are too high in organic material, even the ones which say they're designed for cacti.

I would take either a mix like that, or coir/peat and mix it with 50% pumice, 50% perilite, or 50% chicken grit. The soil ideally needs to be VERY chunky and contain much less actual "soil" than many people realize.

I posted this thread a couple weeks ago and some of the comments directly address what you're asking about: The thread "Brands of peat-free soil or soil mixes" in Cactus and Succulents forum

Thank you for the reply.

Between pumice and perilite, which do you think is better?

They work better for different things. I personally prefer pumice with most succulents because it does not float/work its way to the top like perlite. But in bigger pots, pumice is MUCH heavier than the same amount of perlite. There's no reason why you can't use both at the same time, either.