Nitrogen % – Phosphate % – Potassium % (N-P-K)
You should see some sort of number sequence on all your plant food that you buy. For instance, Espoma’s Holly-tone plant food has a 4-3-4 (N-P-K) label on it. This means that Holly-tone has 4% nitrogen, 3% phosphate and 4% potassium (potash). Nitrogen is food for above ground growth and for dark green colors in leaves. Phosphate is good for healthy root systems and for flower and fruit production. Potassium is good for overall plant health. Now lets take a look at a product that many nurseries use called Garden Elements Bud & Bloom which is a water soluble plant food. The numbers on this label are 10-52-8. That’s why you see so many beautiful flowers at the nursery because it contains 52% phosphate. For general purpose plant foods, the numbers will be equal such as 10-10-10 or 12-12-12.
Don’t worry if the N-P-K percents don’t add up to 100% because there are other plant nutrients and other stuff in the package like calcium, magnesium, sulfur and more.
My high school chemistry teacher (Mr. Herzog) would be proud of my explanation above. While I did not turn out to be a scientist and I don’t remember it from listening to him so many years ago, the internet is a wonderful source for a refresher course!
I pulled the periodic table above from chemistry.about.com.