Astrophytum asterias likes warm climate. The growing speed of asterias is normally quite slow but it is growing quite well in hot summer if you feed a lot of water.
Asterias has a thick tap root. If you feed a lot of water in summer, asterias is rotted out from the tap root easily.
I cut tap roots when the seedling is 2 years old. Fine roots will grow a simmilar manner to cuttings. Fine roots are never rotted out even if you feed a lot of water. I cut roots every year after that.
The photo is asterias Hanazono kabuto x superkabuto, cut tap roots.