New Homeowner’s Guide To Soil

We don't give it much thought, but the soil beneath our feet is critical to the success of our gardens. Here's what to know about the soil in your yard.

“It’s alive!” Imagine this line from a horror movie describing what’s beneath your feet. If the soil in your garden is healthy — meaning it’s not drenched in chemicals, eroded or over-tilled into a powder — it most definitely is alive. In fact, a teaspoon of healthy soil has more microorganisms in it than the Earth has people. And those microorganisms play an important role in plant health, so we should always keep them happy.

So, What Is Soil?

Geologists will tell you soil is the mineral or organic material covering the Earth’s surface. But to gardeners, soil is simply what plants grow in. It anchors their roots and serves as a storehouse for all the elements plants need: nutrients, organic matter, air and water.

How Is Soil Formed?

Soil is formed through the weathering and disintegration of rock caused by physical, chemical or biological forces. Over tens of thousands of years, this process creates multiple layers of soil, called horizons. The top layer, or A horizon, is the most important one. It is composed of topsoil and has the highest amount of organic matter and microorganisms.

Topsoil’s thickness can range from a few inches to well over a foot. Unfortunately, soil erosion has depleted much of this layer.

Why Is Soil Important?

Soil is the medium in which most plants are grown. Without it, only plants that could be raised hydroponically would exist, leaving no large-scale agriculture to feed the world.

Soil also serves other functions, including modifying the atmosphere by emitting and absorbing gases and dust; providing habitat for insects and animals; absorbing, holding, releasing and purifying water; and recycling nutrients to make them available to new generations of plants.

Types of Soil

Garden soils are generally limited to four types. Many soils are a combination, so you’ll hear terms like “sandy loam” or “silty clay.”

Clay soil feels sticky when wet, rock hard when dry. It is heavy to cultivate and drains poorly because it has few air spaces. However, it holds nutrients better than other soils, so clay soil can be productive if drainage is improved. Plants suitable for clay soil include those that can take excess moisture and those with thick, vigorous roots to break through the hard-packed soil.

Sandy soil is lighter and grittier to the touch. It drains freely, is easy to cultivate and warms up faster in spring. Unfortunately, sandy soil dries out quickly and does not hold nutrients because water washes them away. Plants that can withstand drought and are not as dependent on nutrients are good for sandy soil.

Silty soil is smooth and fine, with smaller particles than sand but larger than those of clay. It holds water better than sand and is more fertile than other soil types.

Loamy soil is a combination of sand, silt and clay. It is considered the best soil for gardening because it retains more moisture and nutrients.

What is Soil Testing?

Soil testing provides insight into a soil’s fertility and condition. You can have a soil test done by your local cooperative extension office for a nominal fee. Or you can test it yourself with a pH meter or a home test kit from a garden center. A soil test can tell you whether your soil has any nutrient deficiencies. It can also tell you what the pH is.

What Are pH Levels?

The pH is the measure of acidity. With 7.0 being neutral, a pH below that is considered acidic; above that, alkaline. Most plants do well in a slightly acidic soil, 6.0 to 6.5 pH. The pH can be made more acidic by adding sulfur and more alkaline by adding lime.

How Do You Improve Soil?

Two of the best ways to improve soil are to aerate and amend it. Aeration loosens compacted ground so water and oxygen can penetrate to plant roots. It can be done through tilling, using an aerator or turning soil by hand with a spade fork.

Amending soil is best done by adding a three- or four-inch layer of compost, then digging the compost into the topsoil. Also, keep soil covered to prevent erosion. Mulching with shredded leaves will help prevent erosion and slowly feed the soil.

Where Can You Get the Best Soil?

The best soil is the one best suited to your needs. If you are filling holes or low spots in the garden, bagged topsoil from the garden center is your best bet. Larger amounts for big projects, like installing a new lawn, can be purchased by the truckload and delivered to your yard. Search “topsoil for sale” and the name of your town.

Topsoil is not suitable for containers. Instead, pick a soilless potting mix (sometimes called potting soil). For raised beds, look for a mix labeled for raised beds. Or make your own with one part topsoil and two parts each peat moss and compost.

Luke Miller
Luke Miller is an award-winning garden editor with 25 years' experience in horticultural communications, including editing a national magazine and creating print and online gardening content for a national retailer. He grew up across the street from a park arboretum and has a lifelong passion for gardening in general and trees in particular. In addition to his journalism degree, he has studied horticulture and is a Master Gardener.