Have you ever heard that old saying that good gardeners grow soil, not
plants? Well, it's true. Before putting a seed or plant into the soil,
spend a few minutes with a shovel and take a soil sample for testing.
It isn't hard or expensive. In fact, it is probably the best money
you will spend on your yard all season. Understanding your soil will
help you put your money and energies in the right direction. Too often
people think that if their grass and trees are doing o.k. that they
don't need a soil test. It may be that by chance they are doing all
the right things. More likely, they are applying either too much of
some nutrients or too little. Who knows, if they had spent those few
minutes testing their soil every year or so, their grass might be
twice as nice, their trees twice as lush and their fertilizer bills
half as much. It just makes sense. Why leave it all to guesswork?
How Often Should
Soil Be Tested
Everyone should test their
soil at least once to know where their starting point is. It should
also be tested before you start any major planting effort including
sodding or seeding a lawn, installing landscape plants, putting
in a vegetable garden or adding a perennial border. Always test
first if you plan to plant something with very specific soil requirements.
Once you test your soil and have a baseline, soil should be tested
every few years. If you are experiencing any problems with your
plants (such as poor growth or lots of problems with insects and
disease) its a good idea to test the soil again.
Test Options
Home test kitsare available in most garden centers and mail order
gardening catalogs. These test kits usually run a few dollars and
are fairly easy to use. Unfortunately, their results are not very
accurate. If you do opt for using a home test kit, be sure to follow
the directions carefully. It's also important to use distilled water
with these tests. That way the nutrients and pH of your water won't
influence the test results.
Having your soil tested at the University Soil Testing Lab
is a great option. Their testing services are accurate, inexpensive
and fairly quick (usually a week or less). Here in Minnesota,
the basic soil test costs $7. Forms and soil sample bags are available
through the University, County Extension Agents and many garden
centers.
You can also send your soil sample to a commercial lab for
testing. There are commercial soil test kits sold in garden centers
and advertised in gardening magazines. Commercial tests are usually
very accurate and most offer you more information than the University
test but they are more expensive.
Taking a Sample
Soil samples can be taken
any time of year that the soil isn't frozen. Take the sample before
(or wait at least a month after) you have fertilized. For accurate
test results, it is important to follow a few easy steps to get
a good sample. Remove the debris and grass from the top of a small
area and, with a trowel or shovel, take out a slice of soil that
ranges from just below the surface to 6 inches deep. Take samples
from a couple of different spots and mix them together. If the
area you are testing varies quite a bit or will be planted for
different purposes (such as a flower garden and a lawn), you may
want to send in separate samples. If you can see any sticks, gravel,
bugs or worms, pick them out. Most soil tests only require a cup
or less of soil. If the sample is moist, let it dry a bit before
packaging. Be sure you fill out the form that accompanies your
soil test. Most forms will ask what you intend to plant so they
can customize their recommendations. Avoid taking your samples
from areas that are not representative of your soil such as along
the driveway, against the house foundations or the dog's favorite
spot.
The Results
Soil tests sent to either
the University labs or a commercial lab are usually tested for
soil texture (sandy, loam or clay) and the amount of organic
matter (may be described as high, medium, low or as a percentage).
It will also tell you the pH of your sample. The pH of
the soil tells you how acid or alkaline the soil is on a scale
of 0 to 14. Neutral pH is 7.0, higher numbers are termed alkaline
and lower numbers are termed acid. Most plants prefer a pH between
6.0 and 7.0 but there are exceptions. Some plants demand acid
soil and a few like theirs alkaline. Soils in Minnesota tend to
be alkaline. Nutritional levels are an important part of the results.
These results will probably be in ppm (parts per million) and
should be also evaluated from low to high. Results should be given
for phosphorus and potassium levels, but because nitrogen levels
can vary drastically within a sample and from day to day, nitrogen
isn't usually reported. Additional tests can be run on your soil sample if you
suspect a specific problem such as lead in the soil or excessive
salts. Some commercial labs automatically include results for
several other elements such as calcium, magnesium, sulfur, sodium
or others.
How to Use the Results
Soil test results are usually
accompanied by recommendations customized to your intended use.
Here is where the whole idea of testing your soil runs into difficulty
for the homeowner. The recommendations are likely to be something
like "apply .02 pounds of potassium per 1000 square feet".
Yikes! What you really want to know is which bag of fertilizer
to buy and what setting should you use on your spreader. So how
do you get from their recommendations to the bag and settings?
Don't panic. First of all, understand that you don't have to follow
the recommendations exactly, just as closely as possible. There
are usually some instructions on the results to help you convert
their recommendations into a product. And the University has an
information sheet available on how to make these calculations.
It can be really confusing because when a bag of fertilizer says
it is 10-10-10, that means 10% of the weight of the bag is nitrogen,
10% phosphorus and 10% potassium. So if the bag weighs 40 pounds,
that means the bag contains 4 pounds each of N, P and K. And your
recommendation says you need 1.0 lbs/N/1000 sq.ft. Now if your
yard is 7500 square feet, how do you know how much 10-10-10 to
buy and the setting for your spreader? At least one commercial
lab returns recommendations based on actual products.
A common test result in our area is that the pH will be too high.
For help with how to safely acidify your soil, pick up a copy
of our information sheet on that subject.
Don't let soil tests and trying to interpret their results intimidate
you. Keep in mind that you are welcome to bring your results to Bachman's
and ask a horticulturist to help. It may take them a few minutes to
figure it out too, so be patient.
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