Fertilizer is a difficult product to decode. There are an infinite number chemical make ups and uses. And what works in your garden probably won’t work in your yard. This article doesn’t discuss which type, make up or brand of fertilizer to use or where to use it. Instead this article is geared towards helping you decode those seeming random numbers on a fertilizer bag. If you are trying to figure out what fertilizer to use on your garden or lawn don’t despair! Just give us a call at 704.525.2682 or stop by Blackhawk and and have one of our extremely knowledgeable Lawn and Garden associates assist you in picking out the perfect fertilizer for your needs. We also have a wonderful article on Picking the Right Fertilizer for Your Need (link).

Those Three Numbers

Those three random numbers on the fertilizer bag do actually mean something. They refer to the percentage by weight of Nitrogen, Phosphorous and Potassium that that particular bag of fertilizer contains. So if the bag says 20-27-5 then 20% is Nitrogen, 27% is Phosphorous, 5% is Potassium and 48% (the remainder) is filler material.

Nitrogen is the most important and costliest component in any fertilizer. Because different plants absorb and react to Nitrogen in different ways, four different types of Nitrogen are used in fertilizers. Not all bags of fertilizers use all of the different types. The exact mixture of the four types plays a large part in what the fertilizer should be used for. This mixture also plays a large role in the price of the fertilizer as well. The for types of Nitrogen which are classified by how quickly they are dissolved and available for the plant to absorb are; Ammonia Nitrogen, Urea Nitrogen, Water Soluble Nitrogen and Water Insoluble Nitrogen. You must be careful about which mixture of nitrogen the fertilizer contains. The reason being that the wrong mixture of nitrogen will give your lawn an quick green boost. But it will also cause your lawn to burn, along with spurring a host of other long term problems such as weak root growth and thatching. Phosphorous or phosphate is important to different plants for different reasons. For example, in grasses Phosphorous is essential for root development. While in other plants Phosphorous aids in the development of bulbs of flowering blooms. As a general rule fertilizers that are meant for flowers and vegetables will have a higher Phosphorous content. An example of this is “Super Phosphate” ( 0-46-0) which is meant to fertilize bulbs and flowers. Unlike Nitrogen, Phosphorous can not burn or damage your plants if over applied. In most plants Potassium aids in promoting disease resistance and drought tolerance. It helps give strength to limp stems so that plants are more likely to survive the server wind and rain caused by thunderstorms.

Ammonia Nitrogen is an instant release Nitrogen that is completely absorbed by the plant within 72 hours. The chief advantage of Ammonia Nitrogen is that it’s inexpensive to manufacture. Which needless to say is advantage to the petro-chemical company but not your lawn or garden. Ammonia Nitrogen has the disadvantage of if it’s to heavily applied it will result in a possibly fatal ammonia burn to the plant.

Urea Nitrogen is a fast release form of Nitrogen that is absorbed by the plant within the first few weeks. Bat or chicken guano is a common organic form of Urea Nitrogen.

Helpful Hint: Like Ammonia Nitrogen if over applied Urea Nitrogen will burn your plants or lawn.

Water Soluble Nitrogen is a slow release form of Nitrogen that is absorbed by the plant within three to six weeks. As the name implies this form of Nitrogen breaks down on contact with water. The slow break down and absorption is achieved by the application of a synthetic coating to the Nitrogen. This synthetic coating is the reason that Water Soluble Nitrogen is more expensive to manufacture than Ammonia or Urea Nitrogen.

Water Insoluble Nitrogen is a slow release form of Nitrogen that is absorbed by the plant within four to eight weeks. As the name implies this form of Nitrogen is not broken down by water. Instead it is broken down by time and the exposure to heat. This form of dispersal and absorption is achieved by the application of a synthetic coating to the Nitrogen. This synthetic coating is the reason that Water Insoluble Nitrogen is the most expensive form of Nitrogen to manufacture.