Experts and BHG readers answer.
cactus won't bloom
There's no way to force a cactus to bloom. All you can do is make sure they are getting tons of sun (at least 8 hours of direct sunlight a day) and they should eventually bloom. Also, don't let them get too wet. If you can give them conditions that they need (sun, heat, and only occasional watering) they should bloom eventually. There's no rushing a cactus.