Once your cactus pad had time to scab over the fresh cut part where you took it off some other plant. You would go ahead and put them intact with soil, soil don't need to be kept wet so it does need to be kept moist. Because the plant is going to have to establish a new root system and it's going to grow out of that cut area that you made when you took it off some other plant. There is a couple of different kinds of potting soil to use a new premium grade which has compost and peat moss and the soil in it. It's the premium grade, it's a lot lighter when you have to move the plants in and out, a light pot is more likely to get the kind of care in the movement to the light and kinds of light like that during the growing season during the winter time. It would be brought in more quickly than what it weighs a ton, the cheaper potting soil has a lot of times sand and dirt although they do have the organic components. It usually don't have a lot of peat moss mostly it's some kind of compost and plant material also something that I use especially when I'm not doing talking about critical stuff. This is the leftovers of commercially grown or plants that I have grown here in my green house. The potting soil and stuff you take off the plant just by grabbing the whole of the dead stem and there is your potting soil to recycle. I usually take off the stems cause it makes it easier to break up and when you go to digging around the stems a lot of times can get in the way.