All The "Dirt" About Dirt

It is the foundation of our gardens, and the place where gardening success or failure can often be traced: Soil. We all know about soil basics: loam, clay-based, sand, and silt. There are other factors that influence the health of soil, including mineral content, pH, climate, temperature, and microbial activity. If we want to have more successes than failures, we will need to start understanding everything we can about soil.

In our region, soils can vary from heavy clay in the interior parts of the region to sandy near the lakes. In between are the muck soils of the wetlands and the loamy soils commonly found in forested areas. Sometimes a gardener is faced with several different soil types on his or her property. For example, there may be clay soils in the open areas of a yard, with loamy soil in the woodland areas of the same property.

Soil is actually several layers deep. Each layer is called a horizon, and each horizon can be further subdivided. For simplicity's sake, I will call them all layers, and just discuss the three major layers in broad terms:

The top layer is known as, naturally, topsoil. It has a small, thin layer made of decaying material. Below this is the majority of the topsoil layer. This is the layer where most plants gain their nutrients. Top soil can vary in depth from several inches to more than several feet in depth. It is composed of rock fragments and dust, clay and sand particles, decayed and partially decayed plant and animal material, which is known as humus, and finally, microbes and insects.

The next layer of soil is subsoil. This typically is about 18 inches to 2 feet below the topsoil layer. As many new homeowners know, subsoil is often what is encountered when one first tries to establish a new lawn or garden in the yard of a newly-built home. Subsoil is typically heavier, often with more clay particles than what is found in topsoil. It doesn't share the microbial activity of topsoil, and may not have the nurtrient content and very little humus needed to support plant growth. Plant roots are often scarce in this layer as a result.

The last layer of soil is called the parent soil layer. This is the layer from which other layers are derived, and this basement layer is made of indigenous rock or material that was brought in from glacial activity or volcanic activity. So, if the basement layer is limestone, as it is over much of our region, the subsequent layers above would tend to be more alkaline in nature.

This brings up the question of pH. Without going into scientific detail about hydrogen ions, a simple definition of pH refers to the acidity or alkalinity of a substance. Our soils tend to be overall "sweet". That means that they are calciferous, with a more alkaline pH. This is due to the fact that a good portion of our region's soils are over a limestone substrate. In areas of wetlands and woods, the soils will generally be more acidic. Also, as one travels further north into the region, the soils do tend to be more acidic in nature. What this means to the gardener is that choices in plants will be affected by the pH. For example, if we choose to grow a plant that has different pH requirements than our native soil's pH, we can then amend the soil pH to allow plants that require a different acid-base environment to grow. Why all the fuss? Quite simply, plants will not thrive if they are grown in an acidic or alkaline environment that they cannot tolerate. The uptake of minerals and nutrients will be affected. For example, if we try to grow a rhododendron in acidic soils, it will do fine. If we place it in an alkaline or chalky soil, it is unable to take up critical nutrients; they are "locked up" in the soil and are unavailable for the plant to access due to the pH.

Clay soils are made of many fine particles. These tend to aggregate together, forming a very tight soil structure. Clay soils are often high in mineral content, so they should not be entirely dismissed as being worthless. The basic problems with clay soil is that water takes longer to drain, the soil takes longer to dry out so it can be cultivated, and less oxygen is available for the plants, soil insects and microbes. It is more difficult for plant roots to penetrate and it can become easily compacted by cultivating when it is too wet.

Sandy soils have larger particles. Sand can absorb large amounts of water, but then will drain fairly quickly or dry out sooner than loam or clay. Comprised of silica particles, sandy soils often are not as fertile as clay or loamy soil types.

Loamy soils are soils that have a high humus content and a good balance between sand and clay in structure. This allows the soil to be more friable, or easily worked. Humus content also influences the microbial activity within soil, and encourages beneficial soil insect populations such as earthworms. This is the type of soil that most gardeners strive for.

There are some simple tests that gardeners can do to test their soils. One is to have a soil analysis done. These tests will check pH, fertility, and help analyze soil types. There are many kits on the market for the do-it-yourself types, and there are soil labs where soil testing can be done for a nominal fee. These tests will help determine fertility, soil type, and pH. If you decide to have an analysis done by a lab, they will often give recommendations for soil improvements along with the results. Your county extension office can help you find reliable labs for soil testing in your area.

Another simple test for drainage that a gardener can do is a simple percolation test in several areas of the lawn and gardens. Take a large coffee can or large fruit drink can, cut the bottom out and mark the can with a dry marker in one inch increments starting about 3 inches from the bottom. Place the can into the soil, until the first mark is even with the soil level. Fill the can to the uppermost mark with water, and take timings for each minute up to twenty minutes. After the time has passed, divide the total number of inches drained by twenty minutes to determine the rate of percolation per minute. If your soil drains in less than twenty minutes, then divide by that time in which the water has totally drained.

One simple way to see what the compostion of topsoil is would be to fill a large clear glass quart jar, such as a mayonnaise jar , with water until it is about 2/3 full. Fill the rest of the jar with a soil sample, shake for about two to three minutes. The first layer to settle is usually the sand layer. You can then mark this point. The next layer is the silt layer, and it typically will take an hour or so to settle. Mark the jar at this point. The last layer to settle will be the clay layer, and it can take a day to a day and a half to settle. This will give you a rough idea of the proportion of each of these materials present in the areas that were tested. Each area of yard or garden soil needs to be tested separately. If the bottom layer, or sand layer, is the bulk of the soil sedement, then your soil is sandy in nature. If about 35-50% of the middle layer is silt, your soil is loamy by nature. If the top or clay layer comprises the largest layer that has settled, then your soil is clay based.

Another test that gardeners everywhere are familiar with is to test the soil to see if it is dry enough to cultivate. Take a clod of moist, not soggy soil. Form it into a one or two inch ball, then poke it to see if it falls apart easily. Moist, sandy soil doesn't hold a ball shape easily, it falls apart almost as it is formed. Loamy soil will hold its shape, but then break up easily when poked. Clay soil will resist falling apart when it is prodded.

Both clay and sandy soils need to be amended. Fortunately, the cure for both of these soil types is the addition of large amounts of organic matter. Compost, shredded leaves, manure, and peat moss all help to improve the structure of soil. These need to be incorporated thoroughly into the soil, particularly peat moss, which will repel water absorption if it is not completely worked into the soil.

It can take years to build a decent soil for growing plants successfully. We can speed the process by adding all the amendments that are available, but if we want to get a leg-up on gardening, raised beds and berms can offer a good planting medium for gardens. By adding amendments and topsoil to the raised area, we can start gardening in a given area no matter what the structure and fertility is like in the rest of the yard.

When turning over vegetable gardens in the fall, gardeners can take advantage of the effects of climate in conditioning the soil. Add copious amounts of shredded leaves and compost to the vegetable garden in the fall. Turn the garden over, and leave the soil in large clods. The action of rain, snow, and frost will help to improve the tilth of the soil. You will see a definite improvement in soil structure the following spring!

There are rock dusts and minerals that can help boost soil fertility without harming the microbial and insect activity of the soil. These organic products will not, as a rule, leave trace heavy metal elements or mineral salt build-up in the soil, and many such as seaweed and kelp actually encourage soil microbial activity. pH can be adjusted with the addition of ground limestone, to raise the alkalinity, and the use of sulfur, coffee grounds, and cottonseed meal to acidify the soil.

By understanding our soils and how they work, we can expect more successes than failures in our gardening efforts. Get to know your soil today, make friend with it, help it along! By doing so, you will see an improvement in plant performance and health, and will suffer fewer frustrations when gardening!