the world's most perfect fertilizer + pesticide is Epsom Salt. yup, it really does work!
use it as a fertilizer: one tablespoon per gallon of water. composed almost exclusively of magnesium sulfate, Epsom Salt is intensely rich in these two minerals that are both crucial to healthy plant life.
use it as a pesticide: sprinkle on + around plants rendering them foul-tasting to garden pests.