Reading the Fertilizer Bag

— Written By Donna Teasley and last updated by
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When you buy a bag of fertilizer, do you ever wonder exactly what’s in it? It’s really very easy to know what is contained in that bag if you know how to read the code. The code is the 3 numbers on the front of the bag such as 10-10-10. These numbers can be different but they all mean the same thing. Each number represents the percentage of the 3 major nutrients contained in that bag. The numbers are always in the same order, nitrogen is first, phosphorous is in the middle and potassium is last. This means that a 50 pound bag of 10-10-10 has about 16 pounds of nitrogen, 16 pounds of phosphorous and 16 pounds of potassium in the bag.

What do these nutrients do? Well, nitrogen is for top growth and makes the plant nice and green. Phosphorous helps with flowering and also insures healthy roots. Potassium promotes the general health of the plant and helps with disease resistance. Some fertilizers also contain micro-nutrients such as iron. The numbers tell you what crop that fertilizer is best suited for. If you’re sowing a new lawn, the first and second numbers should be high to help the grass germinate and grow roots quickly. Fertilizers such as 10-10-10 and 17-17-17 are for general purpose uses. High phosphorous fertilizers are often applied around rhododendrons to help them set blooms for next year.

It is always best to use these nutrients in a balanced fertilizer blend. In other words don’t go out and just put phosphorous on your lawn. That can get things out of whack. You can also choose quick release or slow release fertilizers. The quick release feeds all at once but the slow release feeds the area for a period of three to four months. Either is fine to use but obviously the slow release fertilizer has a more lasting effect.

Fall is the best time to fertilize the lawn. Trees and shrubs should not be fertilized at this time. Follow the application rate on the bag and your lawn will be ready to go next spring. If you need help choosing the best fertilizer for your needs, give the Extension office a call at 764-9480.