(Originally published in the April, 2012 edition of the Bayview Bylines, edited by Mandy Skala)

As I look out my window at the fat, fluffy snowflakes piling up (Yes, it’s time to shovel off the deck again!), I find it hard to believe that spring has sprung and that a new planting season will soon be upon us. It is the end of March, however, so now is a good time to take stock and get ready for a successful garden.

In my last post, I talked about organizing your seed and plant purchases which is one of the most enjoyable parts of gardening (unless you count eating warm, ripe strawberries straight out of the garden!). Today, I want to talk about something all our plants depend on but which we generally take for granted: the soil beneath our feet. Notice I said “soil” not “dirt.” “Dirt” is something my dogs and kids drag into the house that has to be swept or vacuumed up. “Soil” is the rich, complex structure which supports plants and, as a result, all life on the planet.

We often think of soil fertility in terms of nutrients – nitrogen, phosphorus, potassium and the other nutrients need for plant growth, but fertility is a bit more complex than that. Soil fertility really has four components:

* Structure
* Organic Matter
* pH
* Nutrients

Soil structure is determined by the proportion of sand, silt and clay in your soil. Good garden loam is usually made up of roughly equal parts of these three soil types. You can determine the structure of your garden soil with a simple squeeze test. Get a handful of soil from your garden and moisten it with a spray bottle. It should be moist enough to hold together in a ball but not soaking wet. Give the ball of soil a hearty squeeze, then open your hand.

If the ball of soil holds its shape, poke it with your finger. If it crumbles, you have the classic garden loam we all dream of! If, when poked, the ball stubbornly refuses to crumble and holds its shape, your soil is heavy on the clay side. If, when you open your hand, your ball of soil immediately falls apart, you have sandy soil. These last two types of soil can be improved and corrected by applying organic matter like compost to the soil. Compost will “lighten” clay soils and improve the water holding capacity of sandy soils.

Mentioning compost as a means of improving soil structure brings us to the next component of soil fertility – organic matter. According to the Soil Ecology and Management website of Michigan State University, soil organic matter is defined as, “already decayed plant materials after they are no longer identifiable as the original plant and have been biologically degraded to a humus material or soil organic matter. “ Organic matter is important in soil fertility because it:

* is a source of plant nutrients (for example, nitrogren),
* improves soil structure (see previous paragraph),
* holds water and dissolved nutrients next to the plant roots for better absorption, and
* helps control erosion.

Organic matter can be increased in the soil by adding compost or well-rotted animal manure or by growing and plowing under green manure crops like vetch or clover.

The third factor in determining your garden soil fertility is pH. Has anyone else ever wondered what those two little letters really mean? Well, they stand for
“p”otential “H”ydrogen. My husband, the PhD in chemistry, would tell you that
pH describes a substance’s ability to attract hydrogen ions. This is very nice, I’m sure, but doesn’t help me a lot unless I get that question in Trivial Pursuit.

To a gardener, pH tells us whether a soil is more acid or more alkaline. We care about this because some plants – blueberries, evergreens, azaleas, etc. – won’t flourish unless the soil they’re grown in is very acidic (less than 5.0). On the other hand, crops like asparagus and lilacs require a more alkaline soil to do their best. For most garden purposes, though, the ideal pH is right in the middle between 6.5 and 7.5 or neutral.

The final category of garden fertility – nutrients – is what most people think of when they talk about “fertility.” The three major nutrients that all plants require are nitrogen, phosphorus and potassium. The percent of these three elements are displayed in N-P-K order on every bag of fertilizer you buy.

Plants require other nutrients in smaller amounts. Micronutrients like sulfur, calcium boron, magnesium, etc. are also provided by many complete fertilizers, but you have to read the fine print on the label to find out what and how much.

If you have never done so or haven’t done so in the past 3-5 years, this spring it may be time for a soil fertility test. These tests are very useful in determining existing soil nutrient levels in your garden as well as identifying plant nutrients that may be deficient. This helps you spend your fertilizer dollars wisely and also guards against over fertilizing that can be toxic to your plants as well as contribut to ground and storm water pollution.

To take a good soil sample, you’ll need to collect soil from 10-12 different locations in your garden. Using a spade or trowel, collect the samples in a random or zig-zig pattern over your entire sample area. Make sure each sample is 6-8 inches deep (as deep as the topsoil in which your plants will grow). Discard any plant material, thatch or stones and mix your samples together in a plastic (not metal!) bucket. Dry your sample thoroughly and put 1-2 cups of your mixed sample in a properly labeled soil sample bag. These soil sample bags can be obtained from your local Extension Office for sending to the state testing laboratory. In Idaho, that’s the Analytical Laboratory Service (ALS) at the University of Idaho. The ALS charges $35.00 for a Standard Fertility Test (N-P-K and pH) and $47.00 for an Extended Fertility Test (N-P-K, pH, organic matter and boron). Private labs offering soil test services can be found on the web. Let the buyer beware, however! Avoid soil test services that sell their own soil amendments. You may not get an accurate and unbiased evaluation from someone who is trying to sell you something!

When you receive your soil test report back from the lab, you can take it to the Extension Office for help with interpreting results and fertilizer recommendations. It’s up to you whether you use organic or inorganic fertilizer. Just remember: inorganic fertilizers feed only the plant while organic fertilizers feed the soil.

Well, I could talk “soil” all day, but, now that it’s stopped snowing, I have to go shovel off the deck. Happy first week of spring everyone!

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