they will thank you later with improved growth
remove plants from pots ... knock off as much as the old potting soil as possible .... while being careful not to break any stems, roots or scar the caudex
then - in separate container - mix the sand, rock and lump charcoal to the old potting soil ....
while you have the plants out of the pots ...as you repot, sprinkle / layer in a pellet type slow release balanced fertilizer such as 13-13-13 or 14-14-14 ....this will provide the nutrients necessary for flowering and thickened caudex
wait a couple of days ...then water thoroughly to saturation ....4 or more passes may be required - insure water drains freely from drainage holes
