If you’ve brewed a pot of coffee, don’t throw away the leftover java. Coffee is loaded with more than just caffeine: It contains potassium and magnesium, which are two nutrients plants love for growth. But because straight coffee can be too acidic, it’s best to mix leftover coffee with water. By diluting it (1 part coffee to 1 part water), you’ll give a kick-start to acid-loving plants like ferns, flowering bushes and roses. And don’t forget old coffee grinds -- just sprinkle them into soil to add a natural boost.