Understanding Fertilizer Numbers and Labels

Have you ever went to the hardware store and been overwhelmed at the choices of fertilizers for your homes lawn and garden? I hope to break it down in an easy to understand way and give you some confidence that what you are buying and applying is the right product and ratio for your given application. The great majority of fertilizer options that home owners have will be in the form of a granular fertilizer so that is what I am going to be focusing on within this artificial. The first thing I am sure that you noticed as you looked at the bag of fertilizer are the three large numbers at the top of the bag usually separated by a dash. For example a common early spring fertilizer from a garden center such as home depot would be a fertilizer with an analysis print out of 18-0-9 often times it will also contain some form of pre-emergent for crabgrass and annual weed control. I will get into the pre-emergent later in this article but for now lets just focus on the always misunderstood numbers that are for this example 18-0-9. The first number in this series of numbers always represents the percentage by weight of nitrogen in the bag of fertilizer you are looking at. Nitrogen is absorbed by the plant through the root system and used to produce nucleic acid and various enzymes/proteins that allow the plant to actively and efficiently participate in photosynthesis. This is why a plant with a deficiency of nitrogen will exhibit yellowing and slow growth because a degradation of the chloroplasts within the plant inhibit photosynthesis. Needless to say nitrogen is very important for healthy lawn and plants.

The second number in the trio stands for the percentage of phosphate. In our above example of 18-0-9 we have a fertilizer with 0 percentage points of phosphate. Phosphate is used by plants to establish a strong and healthy root system, it is however not deficient in most Midwestern states soil and often times not required for established lawns. In fact many states have made it illegal to commercially apply a phosphate containing fertilizer to an existing lawn. The reason behind this ban is that over application of phosphate containing fertilizers contaminating storm water run off led to many of the huge algae blooms that have been on the news harming lake Erie and many inland water ways. Algae steals the oxygen from the lake and chokes out native fish and plant species. Phosphate is however allowed to be used on newly installed sod or grass seed within the first year to promote root development. Phosphate is also very helpful when planting or transplanting garden plants for the same reason.

The last number in our example 18-0-9 represents the percentage points of potash in the bag of fertilizer by weight. So in our example our bag had 9% of its overall weight in potash (k). Potash stands for Potassium. As you may remember from chemistry in high school potassium is an alkaline metal that is also an electrolyte, another interesting characteristic of potassium is its violent attraction to water. Potassium in fertilizer helps reduce transpiration it also helps strengthen the vigor of the plant material.

Lastly I mentioned in the beginning of the article I would discuss the two most common pre-emergent chemicals that the homeowner is likely to encounter. Most often a homeowner will see that a given fertilizer contains either prodiamine or dimension in conjunction with the slandered fertilizer. They both prevent crabgrass and other annual weeds from germinating for a period of between 90 to 120 days after application. The most important thing for proper crabgrass control is ground temperature when applying, and properly watering in your pre-emergent of choice. I hope that I was able to shed some light on this topic for you all.