Digging up the dirt

The Baltimore Sun

As most gardeners have learned, you are only as good as your dirt.

A surefire way to know the quality of your soil is to send a sample to a laboratory for analysis.

Even experienced gardeners, experts say, should test their soil every five to 10 years to see if any nutrient imbalances have developed. Garden soil, they say, is like a fine-tuned engine: The chemicals and nutrients have to be working in balance so plants can make food.

I have often felt that testing your soil was a lot like changing your diet or starting a new exercise regimen. It is one of those things you promise yourself you are going to do, someday soon, but never quite seem to get around to.

But after years of procrastinating, I recently took up the trowel and took samples. The gray days of March present opportune times to sample soil. First of all, it is logical that you should ascertain the health of your ground before you start putting plants in it, so you don't wonder if they are going to thrive.

As Coleen McCarthy, head of City Farms, a program that rents garden plots to folks in seven Baltimore locations, put it: "Testing your soil is a lot easier than going through the growing season using trial and error."

Logic, of course, is not always a big factor in gardening. Especially when it runs up against the overwhelming urge felt on warm spring days to dig and plant with abandon.

Fortunately, Maryland's weather does a good job of keeping such urges in check. On most days of March - a month God invented, according to author Garrison Keillor, to show people who don't drink what a hangover feels like - a short session outdoors digging up a few soil samples is all a body can stand.

That certainly was the case one day this week as I stood shivering in the cold, watching John Polhemus demonstrate how to take a soil sample. Polhemus now is a recreational gardener in Druid Hill Park, but for 37 years he cultivated 100 acres in New Jersey's Warren County, growing corn and other vegetables. In his farming days, Polhemus regularly took dozens of soil samples, using a special tool called a soil probe. These days, he uses a shovel and garden trowel to draw a sample at the "tillage level," about 6 to 8 inches below the surface for vegetables.

Getting your earth analyzed gives a grower two advantages, he told me. "One is you actually know how much fertilizer you need to use." Overfertilizing, the experts say, is the bane of many gardeners and can throw off the chemistry of your soil. Moreover, because of runoff, excess fertilizer can make its way to waterways, damaging aquatic life.

Another advantage of the test, Polhemus said, is that the analysis gives you "a feeling for your soil."

Chafing under a harsh wind, Polhemus drew four samples from random spots in his three 10-foot-by-15-foot garden plots. After opening the earth with a shovel, he used a trowel to remove a slice of soil about 6 inches below ground level. He tossed each of these slices into a plastic bucket, then stirred them with a wooden stake. The stirring, he explained, mixed the soils so that the test results would reflect the condition of his entire garden, not just one spot.

The next step was drying the soil indoors near a radiator (never in the oven). You don't want to send wet dirt to a testing lab. Wet dirt weighs more than dry dirt, which means the postage is higher. Besides, the lab workers frown on wet dirt, which is messy to work with.

The one-cup sample of dried dirt, free of rocks and clumps, from my garden was poured into a reclosable plastic freezer bag. I marked the bag with the name of my sample and enclosed a form detailing what I was growing and what tests I wanted. I opted for the standard soil test with an organic matter measure, a $13 expense. And I mailed it to the University of Massachusetts Soil Testing Laboratory in Amherst, one of about eight labs (none are in Maryland) that charge a modest fee for soil tests.

When I presented my parcel to the clerk at the Hampden Post Office, she asked if there was anything of value in the brown manila envelope. "Just dirt," I replied. "Dirt?" she said, looking puzzled as she weighed it. She said I owed Uncle Sam $1.13 for postage.

Less than a week later, the two-page results arrived in the mail. One page was the analysis of my soil. The other contained recommendations.

The news was good. The pH level, the measure of the acidity or alkalinity in the soil, was 6.9, almost ideal, Steve Bodine, director of the lab, told me over the phone. The pH should fall between 6 and 7 for most vegetable gardens, he said. So I did not need to add any lime, which you do when your pH is low, or aluminum sulphate, which you do when the pH is high.

As I looked over this report, I initially glowed like a school kid who had received a good report card.

My plot's potassium and phosphorus were "sufficient," the organic matter was "desirable," the micronutrients were "normal," and the lead level was "low."

Perhaps a little composted manure or dried blood could be added to the soil, the report said, to elevate its nitrogen levels. But the report warned me, don't over do it, just add a touch.

Later, Bodine told me that "more often than not, I tell gardeners to back off rather than add more."

After initially feeling proud, a wave of melancholy swept over me as I read the report a second time.

I came to grips with the fact that I had paid $13 and had put myself through the soil testing paces to learn that my ground did not need my help. The soil test was telling me to do nothing. This is a difficult message for a gardener to accept, especially in the spring. So I didn't accept it.

Instead, I poked around in garden books until I found something I could do for my soil. Rodale's Garden Problem Solver book said that in the spring I could add organic matter, a top dressing of an inch or two of composted leaves, that could be worked into the garden soil, provided the ground was not too wet.

My soil has a fair amount of clay in it. When clay gets wet, it can resemble cement. Adding organic matter breaks up the clay and lets more nutrients reach the plant roots. In soil lover's jargon, this is called giving the ground good "tilth."

Another way to give good tilth is to let the worms do the work. That is what Michael Weisman suggested in his 2006 book, The Victory Garden Companion. Weisman wrote that counting earthworms was an accurate way to assess how you are doing in the battle for good dirt. Excavate a one-foot-square piece of ground to the depth of 6 inches, he wrote, place it in a wheelbarrow and count the worms. No worms means you need to dig in 4 to 6 inches of organic matter. "Finding more than 10 worms means you are on your way to victory," he wrote.

Once the weather clears, I guess I will start a worm census.

There was another troubling aspect of getting a good report card for my garden soil. If the ground is in excellent condition, then there could be one explanation for any crop failure. That would be the gardener.


How to take a soil sample

1. After opening the ground with a shovel, use a trowel to take a slice of soil from the tillage level, where the plants will feed. For vegetables this is about 6 inches below the surface.

2. Take several such samples, about four for a 30-by-45-foot plot, and mix them in a clean plastic bucket.

3. Air-dry the mixture and remove rock and dirt clods.

4. Place a 1-cup sample in a soil bag or a labeled zip-top plastic bag and mail the sample, the accompanying paperwork and payment to the lab.

The truths about soil sampling

Why do it:

It helps you determine before you plant if you have nutrient deficiencies in your soil. It also helps in making decisions about fertilizers.

When to do it:

Take samples in the early spring, before you plant and before the soil testing labs get busy.

How to find a testing lab:

The University of Maryland Cooperative Extension Service has compiled a list of regional soil test labs. It is available online at hgic.umd.edu or by calling 800-342-2507 from 8 a.m.-1 p.m. weekdays.

What to do when you get the results:

Garden soils have their unique needs, and the soil testing labs send recommendations for what steps to take to improve the soil for your crop. When you send in your dirt, tell the lab what you are planning to grow in it.

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