Fertilizers and bolting spinach

Could you give me some basic rules about fertilizer? What kind and what brand should I use on the garden? The lawn? Trees? Flowers? Much of the fertilizer that gardeners use is the pelleted kind that we buy in sacks. It offers the basic three nutrients which plants need in the greatest quantities: nitrogen, phosphorus, and potassium. They are the three numbers listed on a fertilizer sack, in that order. Many fertilizers, but not all, also will contain "micronutrients," substances which plants need in very small quantities. Personally, I choose fertilizers which contain some micronutrients. The...