This is the time of year when people discover that they should have sent in for a soil test. Their tomatoes aren’t doing well, or maybe it’s the dahlias. The plants look yellow and sick, and they aren’t producing flowers or fruit as they should.

Maybe you haven’t had a soil test in a decade or more (at least I haven’t) because one, it’s the same darn garden; two, you’ve been gardening for years, so you know what you’re doing; and three, you keep forgetting to get one of those soil test kits from the state.

Bruce Hoskins, coordinator of the soil testing program at the Analytical Soil Testing Lab at the University of Maine, said home gardeners should do a soil test every two to three years, and they have two options. The standard test checks soil pH (acidity), organic matter, all important minerals except available nitrogen, and whether you have problems with lead. It costs $15, unless you send in your samples from Jan. 1 to March 1 while the lab is less busy, when it is $12.

The comprehensive test does all of that, adds available nitrogen, and costs $22. The soil for the comprehensive test should be dug and sent in between Memorial Day and Labor Day, Hoskins said, because nitrates dissipate from the soil quickly.

Now through Labor Day is a good time to get a test done, he said, because you can till in most of the recommended products in the fall and add the nitrogen in the spring.

Soil tests can be done for vegetable gardens, flower gardens, lawns, forests or for specific crops. You should take soil from several areas of the plot you want tested, go as deep as the roots go (6 to 8 inches for vegetables and flowers, 3 to 4 inches for lawns) and mix the samples from each plot together in a clean container before putting them in the box to ship to the lab. You also have to measure how large the garden plot is, so the testers can tell you how much of each soil amendment you should add.

When requesting the test, you need to tell the testers whether the garden is organic or conventional. Hoskins said about 75 percent of the tests are for organic, with 25 percent conventional. Some people request both.

The results report is easy to interpret. Bar graphs describe whether results for specific materials are low, medium, optimal or above optimal. It then tells what amendments to put on, and how much.

For nitrogen in an organic garden, for example, the recommendations offer options of blood meal, soybean meal, crab meal and commercial organic fertilizers such as those put out by Espoma and North Country. Nancy and I use Fertrell organic granular fertilizer that we buy from Fedco, and Hoskins said my mentioning that product was a reminder that he had been meaning to add that to the calculations he offers.

The lab does about 15,000 tests a year, and Hoskins said that he is finding many gardens with low nitrogen this year. This is caused partly by a cool spring and early summer, with periods of heavy rain, which wash out nitrogen. But it is more than that, Hoskins believes.

“There’s kind of an urban legend that you can grow things on compost and don’t need anything else,” he said. “There are lots of nitrogen shortages in gardens where people use compost and nothing else.”

Coincidentally, shortly after I interviewed Hoskins, Nancy got an email from Suzanne Bushnell of Harpswell, recently elected president of the Garden Club Federation of Maine, on a variety of garden-club topics.

At the end, she included this: “We’re having trouble in our veggie garden this year. Sent a sample to the soil-testing folks and it came back that everything is out of whack – the pH, nitrogen (too low), phosphorous (way too high) as well as everything else way too high. Very depressing and probably too late in the season to dig up the garden and start over. We didn’t do anything different except add some compost” from a local garden center. She wondered if the compost was bad. Probably not, but she needed something in addition to the compost.

At least now, she knows what to do for next year. And if I were gardening in Suzanne’s soil, I’d take some time to add nitrogen right now. Gardeners are always optimistic, and I’d be thinking that the nitrogen might get into the plants before frost hits. But – and she knows this now – Suzanne should have had a soil test sooner.

Right after that email and the Hoskins interview, I requested the soil-test form and boxes to test the vegetable garden, at least one flower garden and maybe the lawn. Yes, our garden is doing pretty well this year, but I want to keep it that way.

Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at [email protected]