In this week’s tip, we’ll be scratching the surface when it comes to topsoil, garden soil, and loam. Entire books can and have been written on these topics, but in the interest of brevity, more detailed descriptions will be omitted.
Topsoil generally refers to the top 2 inch layer of ground. This is where the highest concentration of nutrients and microorganisms live. Topsoil can reach up to 12″ deep, with the depth measured down to the subsoil, which is the next layer of hard packed soil underneath the topsoil. While the term is often used very loosely, in Ontario, topsoil has certain requirements it must meet in terms of texture, pH and salt content.
Garden soil is similar to topsoil, but typically refers to soil that has been prepared or amended to be suitable to grow a variety of plants. These amendments can include, but is not limited to composted manure, worm castings, fertilizer and peat moss. Like topsoil, the texture can vary based on the composition of sand, clay, silt, and organic matter. Often the terms topsoil and garden soil are used interchangeably.
Loam refers to a balanced soil with almost equal parts of sand, silt, and clay. The amount of organic matter in loam doesn’t make a difference in classifying soil as loam.
Loam, topsoil, and garden soil are terms that are often loosely used and other interchangeably. Topsoil can be loamy soil, if it is found in the top few inches of the earth and made up of equal parts of sand, silt, and clay. It can also be called loamy garden soil if used in the garden.
To add to the confusion, some garden centers we’ve talked to generalize top soil to mean a product that is inferior to garden soil. In addition, some of the topsoil and garden soil bags commercially sold don’t specify the ratio of sand, silt, clay, and organic matter so you don’t always know what you are getting.
We recommend that if you are looking for soil for your garden, ask as many questions as you can about the composition of what you are buying. Here are some of the things you should ask:
- What kind of soil is it (ex. clay, loam, sand, sandy-loam, clay-loam)
- What is the pH of the soil?
- What kind of ingredients are in the mix?
- Is it certified for use in organic agriculture? (ex. is it OMRI listed)
- Is it tested for heavy metals or other harmful ingredients?
While some soil companies will claim their blend is proprietary and won’t share exact details, the more questions you ask, the better informed you will be. Also assess your needs and requirements. Seeding a new lawn will require different soil than a vegetable garden. If your garden has drainage or flooding issues, different ingredients can potentially help minimize certain issues.