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What Do Those Fertilizer Bag Numbers Mean?

Posted by: Nick DiBenedetto on December 13, 2019

Know What You Are Getting

Getting the right amount of the right nutrients down on your turf is a key part of having a healthy, green lawn.  The three main numbers on most fertilizers indicate the amount of Nitrogen, Phosphorus, and Potassium in each fertilizer.  A complete fertilizer will contain all three nutrients while and incomplete one will be lacking one or two of them.  The numbers appear on the label as N -- P – K; the percent nitrogen, percent phosphate, and percent potash.  This is known as the analysis of the fertilizer.  One hundred pounds of a 36-12-18 fertilizer would contain 36 lbs. of N, 12 lbs. of phosphate and 18 lbs. of potash. 

In order to properly apply fertilizer, one must know the area of turf to be treated (in square feet); what rate needs to be applied and what is the analysis of the fertilizer.  For example, if you chose the above fertilizer to supply 1 lb of N per 1,000 square feet and your lawn is 8,000 SF, how much fertilizer do you need?  You need 8 pounds of nitrogen [(1 lb /1,000 SF) x (8,000 SF)].  Divide the amount of nitrogen you need by the decimal percent of the fertilizer (8/0.36) and you will need about 22 pounds of this product to supply 1 lb of N to 8,000 SF. 

Another important bit of information is how much Water Insoluble Nitrogen (WIN) is in your fertilizer.  This is an indication of how much of the nitrogen is in a slow-release form.  A higher percentage of slow-release nitrogen means it will be less likely to cause burn to the lawn and will give a steady supply of nitrogen to the lawn.  Water-soluble nitrogen typically lasts 4 to 6 weeks in the lawn and slow release forms can extend the time between fertilizer applications.

Beware Of That Middle Number

One of the most important things to know about lawn fertilizer in Massachusetts is that you cannot apply any fertilizer that contains phosphorus except on new lawns being established on bare soil or a complete renovation of an existing lawn.  Applications of phosphorus may only be done the first growing season.  The only exception to this is if a soil test shows your soil to be deficient in phosphorus.  State law requires that phosphorus-containing fertilizers be displayed apart from other fertilizers and the law clearly stated on signage. 

Watch The Soil Conditions Too

There are more laws to be aware of regarding the fertilization of your lawn in Massachusetts.   Fertilizer cannot be applied to flooded, saturated, frozen, or snow-covered turf.  These laws apply to both homeowners and professional applicators.

Get More Info From The Pros!

Looking for more information on fertilizer or just ready to let the professionals take over your lawn care needs? The Grassmaster Plus team is ready and willing to answer any questions you have and can provide you a free quote on your lawn care services for the season. Contact our local office today!