Most commercial fertilizers have 3 numbers on the package divided by dashes. For example: 5-10-5. These numbers represent the percentages of nitrogen, phosphorus and potassium in the product.  A bag of 5-10-5 fertilizer contains 5 percent nitrogen, 10 percent phosphate and 5 percent potassium.  These three components are the primary nutrients that plants need.  The ingredients are always listed in the same order and consequently this fertilizer analysis is often referred to NPK  Each of these elements serves a different purpose in the development of a plant. 

Nitrogen (N) encourages foliage growth and the green color you see.  Not enough nitrogen will lead to yellowing foliage. The pretty green lawns you see in your neighborhoods were probably treated with a mostly nitrogen fertilizer to get the grass to grow more uniform and pretty green.  If you add too much nitrogen to a garden you'll notice lush green plants but small or no fruit or flowers.

Phosphorus (P) helps a plant convert other nutrients into usable building blocks with which to grow. Promotes rooting, blooming and aids in fruiting.  If your plants are small, are producing little or no flowers and have a bright green or purplish cast to them, you have a phosphorus deficiency.

Potassium/Potash (K) is needed for the plant's cell chemical reactions, contributes to over all health and vigor of the plant and is key to fruit formation, as well as branching and blooming.  Too much potassium is not toxic to plants, but could inhibit the absorption of other nutrients.

Along with Nitrogen, Phosphorus and Potassium there are several another nutrients that are also beneficial that plants.  Any additional ingredients or secondary/trace elements will be listed on the side label and include: calcium, iron, manganese, zinc and sulfur.  Different plants have different needs for both the primary and trace elements.  Esbenshade's has a variety of fertilizers that deliver the optimum combination of both NPK and secondary elements for a variety of different plants and gardening needs. Look for a bag that matches your needs.

The best way to select a fertilizer grade is to have your soil tested.