Absolutely! Bringing your Opuntia Humifusa pads indoors will allow you to control the environment they are in. Since they’re dormant, they won’t grow as quickly as they would in the spring, but you can give them a great start for when you plant them later in the year.
Lay the cactus pads on well-draining soil (don’t stand them up–they can fall over easily that way!). Water the soil like you would a full-sized plant, using the soak and dry method. Do your best to not let water sit on top of the pad for too long.
Placing your plant in your South-facing window is perfect! If you feel it’s not getting enough light, you may consider putting it under a grow light. Water when the soil is completely dry, and you should start to see roots within a few weeks!