I live in Sacramento, CA. What is the best fertilizer for my Mandevilla?
I suggest a well balanced fertilizer like 20-20-20 or 14-14-14. It is my opinion that "bloom booster" fertilizers, with an analysis of 15-30-15, or something similar, are too high in potassium, and in the long run, are harmful to the plant. If you were to ask 10 growers of mandevilla, you'd probably get 10 different answers. What works best for one doesn't always work best for another.