The topsoil layer is where nutrients are delivered to plants, where water is absorbed, where sunlight helps to aid the growing process, and where wildlife and microorganisms interact with the plant in various ways. In short, it is where the "magic" happens. In areas where weather conditions or deforestation have caused depletion of topsoil, agriculture can be negatively affected, leading to food shortages, starvation of wildlife, and other disastrous consequences.
What Is Topsoil?
Technically, topsoil simply refers to the top layer of soil in any garden or yard or field. Usually it refers to a depth of between 2 to 8 inches down. Topsoil is the most productive and important section of garden soil.
When Adding Topsoil Can Benefit Your Garden
If you're lucky enough to be blessed with perfect topsoil, you're probably the envy of the neighborhood (or at least your gardening neighbors). But generally speaking, most soils benefit from added topsoil on occasion. Topsoil can wash away in rainy seasons or get moved around during construction projects. Its nutrients can be depleted by too many weeds, too much foot traffic, or exposure to foreign substances.
You may have heard of crop rotation: this practice is intended to benefit topsoil retention and prevent soil erosion or depletion of nutrients by changing the types of plants or crops grown every season. For vegetable gardens, most gardeners like to add 1 or 2 inches of fresh topsoil very year. If your flower or vegetable bed tends to get dried out or is exposed to organic matter that increases its acidity (such as pine needles), adding fresh topsoil will improve its composition and raise the soil pH closer to neutral. To ensure optimal growing conditions, replenish topsoil as needed. Adding topsoil can improve drainage, enrich soil nutrients, and create better soil texture, making planting and weeding much easier.
Types of Topsoil
Topsoil is usually described based on its texture and composition, which are affected by what kinds of minerals and materials soil contains naturally. Oftentimes topsoil reflects the geological nature of its location. Soil types are also categorized based on the size of the particles they contain, which directly relate to their texture. There are six main types of topsoil.
This is a heavy type of soil that stays wet and cold in winter, but tends to dry out in summer. Some clay soils are so thick they're actually used for making clay pottery. Clay soils are often lacking in proper aeration and drainage. They can become easily compacted and is hard to dig in. A clay soil usually needs amendments added to make it suitable for gardening, but some vigorous plants grow just fine in it.
Silt is a fine textured soil. It's usually light in color, and retains moisture fairly well. It tends to have a neutral pH and be fairly rich in nutrients.
Sandy soil is light colored. It's usually fairly low in nutrients and lightweight. It can be useful to mix sandy soil into other heavier soils to get good texture, but sandy soil on its own can be prone to being washed or blown away easily, and erosion is a problem.
Loam combines sand, silt, and clay in a medium textured mixture. It is a desirable soil to have, often being rich in organic matter, with good texture for planting and good drainage. It is dark in color and holds its shape when squeezed together. Loam is usually either mostly sandy or mostly clay.
Chalky soil is light colored, porous, and contains large amounts of limestone or calcium carbonate, making it highly alkaline.
Peat is lightweight and contains organic matter. It has excellent drainage. Peat soils don't occur naturally in very many places, so peat is often harvested and exported for use in soil amendments and mixtures to improve the texture ad drainage of garden soil.
How Does Topsoil Differ from Garden or Potting Soil?
Generally topsoil is much heavier than potting soil. Soils sold commercially as garden or potting soils often have materials added to make them lightweight and fluffy in texture, such as vermiculite or peat moss. They can help lighten clay soils when mixed in; and they're useful for growing plants in containers. Some garden soils have extra organic matter added to give nutrients to food crops and flowers. Potting soils don't tend to hold together well on their own in a garden bed, because they're too lightweight to hold moisture effectively.
How to Apply Topsoil
You can acquire topsoil in various ways. For larger amounts, buying it in bulk can be a good and economical option. Some topsoils sold in bulk will have compost added. Or you can buy it in bags, usually weighing from 20 to 40 lbs.
You can apply topsoil at any time, but most gardeners like to add it in spring before planting. It may also be added in the fall as a top dressing that will allow nutrients to break down into the soil. You may add topsoil into plantings by adding to the holes where shrubs are planted. You may spread a layer of it over the garden before or after planting.
If the soil you purchase is somewhat lumpy you can mix it up in a wheelbarrow or on a tarp before spreading it in your garden. You can also mix in your own amendments beforehand, such as peat moss, compost, manure, or other organic matter. Mix with a small spade or trowel. You can spread the soil by pouring from containers, or applying with a shovel and then leveling it with a rake or a broom. Spraying down the layer of topsoil lightly with water after you spread it will help fix it in place.