Soil sampling can be done any time of the year; however, the
ideal time is 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 F. Be sure to wait six
to eight weeks before testing a recently fertilized area.
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
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
Different 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-foot area.
Soil sampling depths depends on what plants are growing in
that location. Recommended depths are 4 inches for established
lawns, 6 to 8 inches for vegetable and flower gardens, and 6 to
12 inches for trees and shrubs.
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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 half-inch 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 to indicate the 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 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
For a list of soil labs, visit the University of Illinois
Extension Soil Testing Labs website at
[By JENNIFER FISHBURN, horticulture
University of Illinois Extension, Logan-Menard-Sangamon Unit]