Fertilizer Explained

by Roy Carter | Nov 4, 2013

Fertilizer Spreader on lawn.  Image Credit UF IFAS Extension FYN Program

Fertilizers are manufactured from a wide variety of materials to supply plant nutrients.  Once these materials are mixed, it becomes difficult to distinguish the materials present.  In the past, a few unscrupulous manufacturers have taken advantage of this to increase their profit. To protect consumers and legitimate manufacturers from such practices, The Florida legislature enacted the first fertilizer law in 1889 and has amended it many times since enactment.  These laws regulate the manufacture and sale of fertilizer in the state.

The law requires that the manufacturer purchase and affix a label to each bag, package, container, or lot of fertilizer offered for sale in the state.  The law requires that each label show specific information about the analysis and composition of the mixture or material.

Image Credit UF IFAS

The key information comes in the guaranteed analysis section of the label.  It tells the home gardener the ratio by percentage of the primary plant nutrients. The number s are in the order of these primary nutrients; Nitrogen, Phosphorus and Potassium.  For example an 8-8-8 fertilizer would be eight percent nitrogen compound, eight percent phosphorus compound and eight percent potassium compound.

There’s some other information in this section of the label that may seem even more complicated but it’s also important.  The label explains how much chlorine the fertilizer can contain.  Chlorine can reduce the quality of some vegetable and flowers.

It informs the buyer what materials the primary plant nutrients are derived from.  This can assist in determining the quality of the fertilizer.

Probably the most difficult part of the label to read, certainly the hardest part to describe, is the information listed right after the total nitrogen figure in the guaranteed analysis section.  In addition the total amount of nitrogen, the label gives the amount of each of several types of nitrogen present in the fertilizer.  This information will seem confusing, but it also offers a glimpse into how the fertilizer will work in specific types of soil.

Terms such as nitrate nitrogen ammoniacal nitrogen, water-soluble organic nitrogen and/or urea nitrogen can be used by plants fairly quickly.  These nitrogen forms in fertilizer are great for a vegetable garden.  But nitrate and water-soluble organic nitrogen are rapidly leached out of the soil so they don’t last very long.  Ammoniacal and water insoluble nitrogen will stay longer in sandy soils.

Fertilizer with a high percentage of natural organic nitrogen is used by the plants slowly over a fairly long period of time.  This kind of slow release fertilizer would be good for lawns helping them stay green without causing spurts of extra fast growth.

This is a complicated subject, hard to fully explain in one article.  This is the take home message: almost any fertilizer purchased in Florida is a good one if it has the ingredients required for plant health and if the price is fair in terms of the total amount of plant nutrients it contains.

For more information on Florida fertilizer label contact your local UF IFAS Extension office or read this publication on the Florida Fertilizer Label.