The most important test a gardener can take is a soil
test. A soil test is used to determine the level of nutrients and pH in the
soil. Soil tests can reveal why some plants aren’t growing well in a
particular area.
Soil sampling can be done any time of the year.
However, the ideal time is now, when the garden season has ended in the
late summer to early fall. It is desirable to take samples before soil
temperatures drop below 50 degrees Fahrenheit. Be sure to wait six to eight
weeks before testing a recently fertilized area.
The pH value is the measure of acidity or alkalinity
of the soil. The pH scale ranges from 0 to 14, with 7 being neutral.
Numbers less than 7 are considered acid and numbers greater than 7 are
alkaline. Soil pH directly affects nutrient availability. Most soil
nutrients are readily available when soil pH is at 6.0 to 7.5. When pH
rises above this value, nutrient elements such as phosphorous, iron,
manganese, copper and zinc become less available. This explains why pin oak
trees suffer from iron chlorosis.
Plants thrive best in different soil pH ranges. For
example, blueberries and rhododendrons need a soil that is acidic, about
4.5 pH. Soil pH values above or below the optimum range may result in plant
symptoms of nutrient deficiencies.
Soil test results are only as good as the sample
provided to the testing lab. Here are a few steps to follow.
Divide your property into sections according to use
and soil type. Submit a sample for each area of the yard — vegetable
gardens, flower gardens, lawn. In addition, each sample should represent
only one soil type.
Use a clean soil probe, spade, hand trowel or shovel
to collect samples. Avoid using brass, bronze or galvanized tools because
they can contaminate samples.
A soil sample must be representative of the area
being tested. So a soil sample is a composite of numerous subsamples.
Randomly select and evenly space subsamples. Collect at least eight
subsamples from a 100-square-feet area.
Soil sampling depths depend on what plants are
growing in that location. Recommended depths are: established lawns, 4
inches; vegetable and flower gardens 6 to 8 inches; and trees and shrubs, 6
to 12 inches.
When testing the area under a tree, take subsamples
from the trunk to the outer edges of the branches.
If using a shovel, spade or hand trowel, dig a hole
and set the soil aside. Then cut a 1/2 to 1 inch slice of soil from one
side of the hole. Place the slice in a clean, plastic container. Remove
leaves, roots, thatch and debris from the sample.
Repeat this process within the sampling area. Mix
subsamples. Spread the sample on a clean paper and allow the soil to air
dry. Place about 1 pint of thoroughly mixed soil in a bag or box. Then
place packaged sample in a sturdy mailing carton.
Be sure to label each sample with name of area being
sampled, i.e. lawn, vegetable garden, flower garden, rose garden, fruits,
pin oak tree, etc. Also include your name and address. If the soil is from
a bare area, indicate what will be grown in the area.
Mail your sample to a soil testing lab. Expect soil
test results within two weeks. Results should indicate the amount and type
of fertilizer or other soil amendments to apply to the soil.
While soil test results provide a great deal of
information, a standard soil test will not identify poor soil drainage,
soil compaction, over-watering or under-watering or environmental
disorders.
Here are addresses and telephone numbers of nearby
soil testing labs.
Ingram’s Soil Testing
13343
Fitschen Road
Athens, IL 62613
217-636-7500
Sparks Soil
Testing
PO Box 841
Lincoln, IL 62656
217-735-4233
This article appears in Oct 2-8, 2008.
