No I meant make sure the soil is far enough around the edges that light can't get under. I keep mine in a shadehouse, which uses those green fibreglass roofing sheets, probably like 50% or more shade.
Don't water, there are no roots! When you SEE roots, water. Use a small pot just bigger than the base when you get the first few roots, smaller pots dry out faster. Once its established Get a nice big pot,
The length of the cactus can be a rough guide for the diameter. It is almost impossible to underwater, but very easy to overwater. Always water in the evening, never when its hot. Learn to look for the little chins that form between spines when its full of water. Gradualy make them used to sunlight, at first for short periods then extending it.
