to NGA
Where out west are you located? I live in Reno, NV, pretty far out west (unless you are in Hawaii).
Are you talking about time release? As in Dynamite? I don't fertilize my cactus very often - forgetful. But when I do remember, I mix at about half strength. If you fertilize every two weeks (about how often I water), I would use 1/4 strength.
Cactus live in a nutrient deficient, water deficient environment. Everything they can get, they take. That means YOU have to know when enough is enough. If your cactus are planted in the ground, they take a lot less care than cactus planted in pots. In the ground, cactus roots spread out just under the soil surface, to collect as much moisture and nutrients as they can find. In a pot, spreading is not an option so the roots fill the pot making root rot more of an issue (caused by too much water and too much fertilizer).
Hope this helps.
Daisy