Photo by Andrew Haworth
We extension agents are often ridiculed for constantly recommending soil testing.
“My plant died.”—“Take a soil sample.”
“My grass won’t grow.”—“When’s the last time you had your soil tested?”
“My dog ran away.” Maybe not, but you get the idea.
Gardening starts with the soil. Not knowing what’s in your soil or what needs to be added is like baking a cake without a recipe—guessing at the ingredients won’t give you the results you want. It’s the same with soil nutrients. You could guess how much lime or fertilizer to apply, but you probably won’t get the proportions right. You might over-fertilize, wasting fertilizer (not to mention money) and creating pollution from the excess that ends up in ground or surface waters.
If you wouldn’t bake without a recipe, why garden without a soil test? They’re relatively inexpensive ($6 per sample) and easy to do. Testing in the fall allows ample time to amend the soil before spring, but tests and soil improvements can be done any time of year.
Gather a few supplies: a sharp spade or garden trowel that’s not dirty or rusty; a clean, plastic bucket; and some soil sample bags from your local Clemson Extension office (or resealable plastic bags).
To get a complete picture of soil conditions across your landscape, you’ll need to take samples from each different area and order soil reports for each. The report for your lawn, for example, will offer little help for the vegetable garden, shrub borders, flowerbeds, shade trees or fruit trees.
A good sample for each area should consist of eight to 12 subsamples mixed together. Using your spade or trowel, dig a V-shaped hole 6 inches deep for each subsample. Take a slice from one side of the hole, collecting soil from the surface to the bottom of the hole. Repeat this for all subsamples, then combine them in a bucket. Break up dirt clods, remove rocks and plant debris, and mix well. What you’re doing is creating an average mix of soil for that area of your landscape. Scoop out about two cups to submit as your soil sample from that area, and pour it into your soil sample bag. Repeat this process for each landscape area you want to test.
Carefully label each bag to keep track of which area it came from. Take the samples to your county’s Extension office, and pay the $6 analysis fee per sample. Give them an ID name for each landscape area you sampled. Tell them what plants or crops you intend to grow there, what type of soil you have (sand, loam or clay), and your contact information.
In about two weeks, you should get your soil-test report back from Clemson University. A standard soil report will include your soil’s current pH, its levels of phosphorous, potassium and other essential plant nutrients, as well as recommendations for lime and fertilizer additions specific to the plants you are growing.
If this is your first soil test, you may be thoroughly confused by the report you get. Soil reports contain a lot of information that’s interesting to soil nerds like me but won’t mean much to the average gardener. You can download a PDF guide that illustrates how to find the info that will be most useful to you.
What if you can’t find the exact product recommended in your soil report? Try using the University of Georgia Fertilizer Calculator at aesl.ces.uga.edu/soil/fertcalc. It tells you how to blend common fertilizers to match the recommendation or at least get close. You can also use this tool to calculate quantities of organic fertilizers to apply, so long as you know the nutrient content (N-P-K) of those sources. Your local Clemson Extension agent can also help you interpret your soil test results and select soil improvements.
Test your soil about once per year until its pH and nutrient levels have stabilized to the desired ranges. Then you can wait two to three years between tests.
S. CORY TANNER is an area horticulture agent for Clemson Extension based in Greenville County. Contact him at shannt@clemson.edu.
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Make sense of your soil report – Your soil report contains a wealth of information, but not all of it is immediately understandable. Click to download a PDF guide with shortcuts to deciphering what you need to know.
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Get More
University of Georgia Fertilizer Calculator – aesl.ces.uga.edu/soil/fertcalc
Clemson Extension County Office Locater – clemson.edu/extension/county
Clemson Extension’s Home & Garden Information Center – (888) 656-9988