By Clint Waltz
University of Georgia
Volume XXVIII
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From hard-core gardeners to novices, most people know you
have to fertilize
your plants to get the results you want. But reading a
fertilizer bag can be
intimidating if you don’t understand what you’re reading.
Most folks have heard of 10-10-10, but they may not know what
the numbers stand
for.
So what are the numbers?
They refer to the percentage of nitrogen (N), phosphate
(P2O5)
and potassium (K2O). So in a
bag of 10-10-10,
10 percent of the weight of the bag is actual nitrogen, 10
percent is phosphate
and 10 percent is potassium.
Knowing how much nitrogen is in a bag of fertilizer is fairly
easy. The percentage
is listed right on the bag. However, it’s not as simple for
phosphorus and potassium.
To determine the actual amount of phosphorus (P) and
potassium (K) you have
to do a little math. Use these formulas: P2O5
times 0.44 equals P, and K2O
times 0.83 equals
K.
Complete fertilizers
A bag containing all three of these nutrients — nitrogen,
phosphate and potassium
— is considered a “complete” fertilizer. A product with any
of these three
missing is referred to as an “incomplete” fertilizer.
All plants need nutrients for proper growth and development.
But various nutrients
affect plants differently and are needed in varying amounts.
All essential nutrients
are required to sustain vigor so the plant can better resist
environmental stresses,
weeds, diseases, insects and other pests.
When it comes time to select a fertilizer, select a brand
that includes these
three primary nutrients.
