March is the beginning of the spring season and the best time to start fertilizing your cacti and succulents. Do begin fertilizing when the cactus shows some new growth. Two major types of fertilizers are: 1) Water-soluble solution (15-16-17) that you dilute in water and use every month or 2) Slow time release fertilizer call “Super Blend” (20-9-9) that you mix with the cactus mix every three months.