Give lots of sun it’s an Opuntia so it can take it and needs it to grow right and tight;). Acclimate of course, but eventually your guy can take all day southern exposure sun. Glochids must be the devil’s work. I would rather repot the Opuntia on the left over the one on the right any day;). The one on the right has been sitting in a gross crappy mix for over a year because I’m dreading the repot. No matter how hard I try I know I’m going to find a few glochids stuck in my skin. This video:) is pretty incredible. Glochids are so misleading because they look completely harmless.

I definitely wouldn’t mist the cactus. I personally would take all the extra stuff that’s in the pot with the cactus out. Along with keeping this cactus dry till spring or at least till is warms up a bit. This is considering you‘re on the northern hemisphere. Put it next to a window and leave it alone. If you feel the need to water, once a month is enough during the winter. Make sure the water drains because I’m not sure what the cactus is planted in has drainage holes. Holes at the bottom of pots make succulent growing much easier;). Once spring comes it would be a good idea to change the soil to a mix that has been amended with perlite and or pumice. You can begin to water more and acclimate to stronger sun when the growing season is here. If you live on the Southern hemisphere you can do this now. Good luck:)!

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1. Columnar cactus Pilosocereus pachycladus 2. Mammillaria nejapensis