What You Should Know about NPK and Fertilizers

Chemical fertilizers and organic fertilizers show their nutrient content with three bold numbers on the package. These numbers represent three different compounds: Nitrogen, Phosphorous, and Potash (Potassium), which we can also describe with the letters N-P-K. The three numbers listed on fertilizer labels correspond to the percentage of these materials found in the fertilizer. What does each nutrient do? In addition to other properties, Nitrogen helps plant foliage to grow strong. Phosphorous helps roots and flowers grow and develop. Potassium (Potash) is important for overall plant health. Be aware that high nitrogen fertilizers will make for quick growth but weaker plants that are more susceptible to attacks by diseases and pests. Fast, showy growth is not necessarily the best thing for your plants.
German scientist Justus Von Liebig was responsible for the theory that Nitrogen, Phosphorous, and Potassium levels are the basis for determining healthy plant growth. However, this theory, which dates to the 1800s, doesn't take into account the dozens of other nutrients and elements that are essential to plant growth such as sulfur, hydrogen, oxygen, carbon, magnesium, etc. Nor does the theory talk about the importance of beneficial soil organisms that help your plants to flourish and to fight off pests and diseases.
While Von Liebig's work was unquestionably important to the science of plant growth and agriculture, other ways of looking at how plants utilize nutrients have largely been ignored, especially by those companies who produce the chemical fertilizers commonly on the market today. For example, if you properly aerate the soil, earthworms, beneficial microbes, and other critters found underneath your garden and lawn will have better access to the oxygen they need to thrive. As they live and digest organic matter, they help to create soil that is healthy and fertile. Healthy soil is the basis for healthy plants. Additionally, if we look at nature, compost in the form of organic humus is ever present in natural plant communities, providing lots of the nutrients that plants need to grow and thrive. Compost contains Nitrogen, Phosphorous, Potassium, and a great abundance of other trace elements that will benefit your plants.
It is clear that Nitrogen, Phosphorous, and Potassium are not necessarily the most important elements you need for your plants to grow well. In fact, elements such as carbon, hydrogen, oxygen, sulfur, magnesium, copper, cobalt, sodium, boron, molybdenum, and zinc are just as important to plant development as N-P-K. (Source: http://www.utexas.edu/utpress/excerpts/exgarhow.html) Over the years, Justus Von Liebig's theory developed into the dominant paradigm for how we grow our ornamental and edible plants. The bad news is that this has lead to a vast amount excess nutrients building up in our streams, lakes, and rivers, because chemical fertilizers are often over-applied. Surprisingly, much of this overuse of chemical fertilizers is actually from homeowners, and not from farmers, who typically carefully measure and apply the least amount of fertilizer necessary to get the job done in order to grow their crops in the most cost effective way possible.

Many homeowners who aren't growing to make a profit end up inadvertently overusing chemical fertilizers (and pesticides too!). They think that if a little bit is good, then more must be better. It isn't! According to the National Academy of Sciences, even though farmers uses pesticides more widely, homeowners uses 10 times more fertilizer per acre. If you only take away one thing from this article, please let it be that you should only use the proper amount of any fertilizer, and not anything more. This will save you money, and it will also keep your yard and garden healthier at the same time. This is extremely important with chemicals, but it also applies to organics! Organic gardeners can look to the work of Sir Albert Howard for solid research and ideas on how to grow plants more naturally. His ideas consider chemical processes that occur in nature. He then applies them to agriculture and home gardening.