How to Get the Dirt
On Your Yard's Soil
It's a dirty job, but many are eager to do it.
Today's home gardeners have been learning the hard way what their rural forebears knew all too well: Good plants need great soil, or, in gardening vernacular, a $1 plant needs a $10 hole.
There are a few plants that don't need soil to grow, but you wouldn't want them around your house. Dirt is most plants' equivalent of bacon and eggs or burgers and fries -- except plants prefer nitrogen, phosphorus, potassium and other minerals to stay healthy, to bloom and to reproduce. Because so many Americans live in new houses, where dirt has been removed for construction and then replaced, the quality of their soil can range from fecund to barren.
Traditionally, soil analysis was done by agricultural colleges for farmers, who need to know what kind of fertilizer to use for maximum yield. Now, a cottage industry of commercial testers has sprung up to give home gardeners the dirt on their earth.
This particular cranky consumer fared poorly in science classes and liked the idea of shipping a soil sample to professional laboratories for analysis. But many gardeners prefer the do-it-yourself kits sold at most garden centers and by mail order. We tried some of each: two labs, one at a university and one commercial, and three home tests, all of which promised to be user-friendly even to chemistry dunces.
We collected the soil sample from our Garrison, N.Y., garden according to rigorous guidelines prescribed by the University of Massachusetts at Amherst: digging down about six inches in a dozen parts of the garden, mixing the samples and letting them dry. We harvested enough dirt for all five tests.
We shipped about two cups of soil to the university and requested the standard soil test. Two weeks later, a report arrived in the mail. Our soil is too acid, has medium levels of phosphorus and potassium, and its nitrogen (NO(3)-N) level is "10 ppm." Huh? Although the explanatory pamphlet emphasized that nitrogen "is essential" to plant growth, there was no indication whether our 10 ppm (parts per million) was low, medium or high. Steven Bodine, director of the lab, says testing for nitrogen is tricky and only extreme results, such as 50 ppm, are useful for making recommendations.
The lab's advice for amending our soil had a one-size-fits-all quality and involved mixing in copious amounts of manure, wood ash and bone meal. In our neck of the woods, putting bone meal in the garden is like laying out a smorgasbord for woodchucks.
A St. Louis laboratory, EarthCo, offers a basic soil test whose results can be easily downloaded from the company's Web site. The report is colorful and easy to understand, offering both numerical data and an interpretation: Our 4.8 pounds of potassium per 1,000 square feet is low. But the results were significantly different from the university lab. EarthCo found the acidity of our soil "adequate," the phosphorus high and the potassium low. And although the report included a two-page list of fertilizers to correct a nitrogen deficiency, the lab doesn't test for nitrogen. The two labs' measurements of organic content in our soil differed by more than 100%.
Our home-chemistry experiments began with the No-Wait Soil Test Kit, which required some waiting. Ordered by mail from Heirloom Seeds in West Elizabeth, Pa., the kit demanded, not just suggested, using distilled water, which required a trip to the grocery store. All of the do-it-yourself kits involved some variation on comparing the color of test fluids to an enclosed palette. Again, with No-Wait, the nitrogen was the fly in the ointment; after four attempts, the test fluid remained stubbornly clear when it needed to turn pink or, even better, red. In direct opposition to EarthCo, No-Wait found our phosphorus low and our potassium high.
The Rapitest Soil Test Kit, made by Luster Leaf Products Inc. in Woodstock, Ill., isn't particularly rapid if, like ours, your soil is more clay than sand. To create a liquid sample, your soil must settle in water, which can take as long as 24 hours. Then you mix some of the liquid and capsules of mysterious powder in four containers and match the resulting hues with the patented "color comparators." Once again, we flunked nitrogen. We had surplus potassium and adequate phosphorus.
AccuGrow Soil Test Strips, made by Environmental Test Systems in Elkhart, Ind., came with a 24-page manual introduced by a cartoon gardener named "C. Moore Green." This was by far the simplest test. After a brief preparation of soil with solutions identified only as M and A, two strips (each with two test patches) were inserted in the fluid for a minute or less. All four patches roughly turned the desired colors, although some of the gradations were subtle indeed and required squinting. (This test in turn showed low potassium and nitrogen and too much phosphorus.)
Sylvie Brouder, associate professor of plant nutrition and soil fertility at Purdue University in West Lafayette, Ind., explained why the tests showed such different results. Most soil-testing labs were developed for regional growers, and their methods and equipment have evolved to support different areas' growing conditions. Choosing a lab close to home is most likely to yield useful results. Ms. Brouder also suggests asking for recommendations from a local nursery or garden center.
The home kits can point arrows in the right direction -- especially regarding the acidity of your soil -- but shouldn't be regarded as exact science. A balanced fertilizer (we use organic because we have omnivorous dogs), healthy additions of compost and a layer of mulch will treat most soil problems. And don't forget to water.
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