When Fertilizing, Read the Label

You can’t judge fertilizer by appearance.  Fortunately, state law requires each fertilizer label to include specific content facts.  However, these can be confusing.To obtain the proper types of fertilizers for various applications, you must understand the label.  At the top you’ll find the identification of the manufacturer or distributor.  Of course, this doesn’t tell how well the fertilizer will help your lawn, ornamentals, or vegetables.

Next, if the term “organic” is used, these will be a statement identifying the type of material, as well as how much is natural, and how much is synthetic.  This is an important indication of how the fertilizer will react in your soil.  For example, natural, natural organic nitrogen is released slowly.  A fertilizer containing a high percentage of this material would be good for lawns, helping them stay green, without causing spurts of extra fast growth.

The key information is found in the guaranteed analysis section of the label.  A series of numbers, such as 8-8-8 or 10-10-10, tell you which, and how much, of the primary plant nutrients the fertilizer contains.  That is, the numbers show the guaranteed amount of nitrogen, phosphorus, and potassium.  For example, a fertilizer labeled 10-10-10 contains ten percent nitrogen, ten percent phosphorous, and ten percent potassium.  Thus, a hundred pounds of this product contains 30 pounds of plant food.  The other 70 pounds is conditioner and filler, required for even spreading.  These may include some incidental trace elements.  If the fertilizer contains significant amounts of secondary plant foods, such as calcium, magnesium, copper and others, they will be listed near the bottom of the tag.

The most difficult part of the label to understand is the information listed right after the total nitrogen figure, in the guaranteed analysis section. In addition to the total amount, the label gives percentages of each of several types of nitrogen in the mix.  This tells you a lot about how the fertilizer works.

You’ll see the terms nitrate nitrogen, ammoniacal nitrogen, water soluble organic nitrogen, urea nitrogen, and water insoluble nitrogen.  Plants use nitrate, water soluble organic, and urea nitrogen fairly quickly.  They might work well in a vegetable garden.  But, they won’t last very long, because they’re rapidly leached out of the soil by rain and irrigation water.  On the other hand, ammoniacal and water insoluble nitrogen will last longer in sandy Florida soils.

Following the basic analysis, is a statement of the maximum amount of chlorine the fertilizer contains.  Excess chlorine may be injurious to certain plants, both vegetables and ornamentals species.  Small amounts can be beneficial under some condition.

Unfortunately, I can’t fully explain anything this complicated in one short article.  I hope I’ve clarified a few of the basic points.  To obtain the proper fertilizer for your specific vegetable and ornamental gardening needs, you must understand the information on fertilizer labels when in doubt; we suggest you check with your County Extension Agent.

For More Information:

The Florida Fertilizer Label