The Homeowners Column

The Homeowners Column

Don’t fail to take this test

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

We spend our lives with test anxiety. Math tests lead to driver's license tests, pregnancy tests and blood tests; we fret about them or avoid taking them. One test carries much less baggage, but is probably the most important test a gardener can take.

This is a good time to soil test. Soil samples can be taken anytime the soil temperatures are above 50 degrees F, but late summer or fall is the best. Soil testing can help determine the cause of problem areas. You know that spot "where nothing will grow." Also it may reveal why some plants are not growing well.

Sampling soil is relatively painless and takes just a couple tools; a clean bucket and a trowel or shovel. If your soil seems the same throughout, then take samples from 8-10 different areas of the test site and mix together in the bucket.

To take the sample use a trowel or shovel to dig a hole, then cut a thin slice down one side of the hole. Do not include roots, twigs, thatch or debris. For lawn areas the sample should be taken at 3-4 inches deep, for flower and vegetable gardens at 6-8 inches deep and shrub and tree areas at 12 inches deep. Multiple samples may be needed if soils appear different.

Spread the mixed sample on clean paper to air dry. Do not sample wet soils. The final sample should be about a half-pint of soil and a composite of the site. Check in the telephone yellow pages for soil testing labs near you. Be sure to list on the sample the intended use of the area. The results from soil testing labs are much more accurate than home kits.

Soil tests will show the soil pH. pH measures the acidity or alkalinity of the soil on a scale from 1-14 with 7 being neutral. Numbers above 7 are considered alkaline and numbers below 7 are considered acidic. Plants have ranges of pH in which they grow best because certain nutrients such as iron are more available at certain pH ranges. Most plants do fine with pH between 6.0 and 7.5.

Blueberries and rhododendrons, however, need a soil that is acidic at about 4.5. They can suffer from iron deficiency in our higher pH soils. Deficiency will show as stunted growth and the leaves may be yellow with green veins. Sulfur is used to lower the pH.

Lime is added to raise the pH. Always get a soil test before adding lime. It is not an annual recommendation in our area.

Once the results are returned, fall is also a great time to add soil amendments. Fall application allows a few months for the slow reacting amendments to work.

For instance if you are planning a blueberry bed or rhododendron bed, prepare the soil now for planting in the spring. Add lots of organic matter with peat moss or compost and add the recommended amount of flowers of sulfur. This should be mixed well into the planting area. How much sulfur to add? It depends. Soils with more organic matter take more sulfur to change the pH. For example an original soil pH of 6.5 of dark colored loam will require 112 ounces of flowers of sulfur per 100 square feet to change the pH to 4.5.

Soil tests will also give potassium, phosphorus, and organic matter levels. Confused by your test results? Contact your local U of I Extension office.

Don't Miss...

Saturday, September 23 at 10:00a.m.
Tree Walk along west University Avenue. Meet at corner of University and Victor in Champaign.

Tuesday, September 26 at 1:00p.m.
Statewide telnet "The Midas Touch-yellow leafed plants" at U of I Extension, 801 North Country Fair Drive in Champaign. PH: 217-333-7672 to register.

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