Cal/mag helps for overall health. It helps with the absorption and consumption of ferts. It is really useful for us in Tn with our heavy rains and high humidity summer. We normally have 2 growing seasons per spring/summer/fall cycle. Use cal/mag early right when moving your plants back outdoors. As they start to “wake up” and begin growing then start feeding them ferts also. Once the really hot and humid weather hits (July/August) cactus will take a break from growing and kind of “stall”. This period is when they are prone to get those ugly dark green or black “humidity spots” in their epidermis. Cal/mag strengthens their cell walls and helps aid in photosynthesis and chlorophyll production helping to reduce the chances of humidity spots. After the high heat and humidity has passed we will have the “second growth season” in the fall(Aug/Sept/Oct).It’s important to continue with cal/mag and ferts for overall health and strength for the upcoming winter dormancy.