Tom Ingram: Ask a Master Gardener
Sunday, June 7, 2020
Q: With all the different fertilizers out there,
how do I know which one I should be using? AR
A: Fertilizers can be confusing. They come in a variety of
strengths with a variety of numbers and for the beginner or novice, it can be
overwhelming. So let’s break it down.
The fertilizers you find at the store
have a series of numbers on the bag. These numbers can be something like the
following: 10-20-10, 19-19-19, 3-17-17, 31-0-4, 46-0-0, etc. Those numbers
coincide with the percentage of nitrogen, phosphorus, and potassium in each
particular product. So, if a product says it is 10-20-10, that means it
contains 10% nitrogen, 20% phosphorus and 10% potassium. If it says 46-0-0,
that means that it contains 46% nitrogen, 0% phosphorus and 0% potassium.
So how do you know which one you should
use?
The best way to know for sure is to have
your soil tested. This may sound a little intimidating, but it is a simple
process.
First, you will need to collect the soil
sample. You can collect this sample using a specialized soil sampling tool or
just use a garden trowel. A bulb planter works well also. The trick is to get
between 15-20 samples from the area you want tested. These samples need to
contain soil to a depth of 6 inches. If this is your yard, get 15-20 samples
from various points in your yard, put them in a bucket, mix it up, remove the
twigs and fill something about the size of a sandwich bag from the soil in your
bucket. If you are wanting a soil test for your vegetable garden or your flower
bed, get your 15-20 samples from those areas.
Once you get your soil sample in a bag,
bring it to the OSU Extension office, 4116 E. 15th St. Even though the office
is closed, there is a black mailbox on the south side of the building (in the
back) where you can fill out a form and leave your sample. There is a $10
charge for a soil test. We will pick it up and forward it to OSU, where they
will test for pH, nitrogen, phosphorus and potassium. Once tested, you will get
a recommendation on what nutrients are needed for your situation. These
recommendations will vary depending on what area you are sampling and what you
are growing.
Once you have the results of your soil
test, you will know how much of each nutrient you need to add to your soil for
best results.
So back to the fertilizer. Let us say
the test revealed your soil only needed nitrogen, and it was recommended that
you add 1 pound of nitrogen for every 1,000 square feet. In this case, you
could purchase some 46-0-0 fertilized because it is 46% nitrogen and does not
contain phosphorus or potassium. This means that if each pound of fertilizer is
46% nitrogen, you would need about 2 pounds of fertilizer to give you 1 pound
of nitrogen. If you purchased 10-20-10, you would need 10 pounds of this
fertilizer to give you the 1 pound of nitrogen. Plus (in this case) you would
be purchasing phosphorus and potassium that you didn’t need and which might
also be harmful to your growing environment.
Yes, you may need to use a calculator,
but odds are that getting a soil test will not only be good for your soil but
also will ultimately help you save money by not having to purchase nutrients
you don’t need.
Garden tips
•Do
not work soil if it is too wet. Tilling it while wet will cause damage to the
structure and it will take a long time to recover.
•Thatch
is a layer of dead and living stems, shoots and roots which pile up on top of
the soil at the base of lawn grasses. If it is over ½ thick it should be
removed with either a core-aerator or power-rake. Now is the time to de-thatch
Bermuda and zoysia. De-thatch fescue, if needed, in the fall.
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