The secret to any thriving garden and lawn is their being rooted in good, healthy topsoil. But, what exactly is healthy topsoil? And what sets it apart from any old dirt?
Well, like dirt of all kinds, topsoil is essentially a mixture of sand, silt, and clay. Sand particles are the largest, while clay particles are the smallest. Silt is somewhere in the middle. The best soil has more silt than sand and clay. Sand tends to allow too much water to drain through, while clay often retains too much water. Silt keeps the moisture balance just right. Sand or clay can be added to soil in order to adjust the drainage as needed.
What sets topsoil apart from just plain soil is its organic matter content. Decaying plant and animal matter breaks down and releases a full range of organic nutrients into the soil, binding the silt, sand, and clay particles together into soil aggregates. In between all these particles are spaces of various sizes, which are called pore spaces. The larger of these allow water, nutrients, and air to enter the soil, and gases to escape.
In addition to the soil aggregates, nutrients, water, and air, topsoil also contains billions of microorganisms. These unicellular animals break down organic matter, releasing nutrients that the plants can then absorb. Most of these organisms require oxygen to live, which means that the soil must be well aerated. Healthy microorganisms lead to rich soil, which leads to plants having the best nutrition.
These are the main components that make up topsoil, making those top three to eight inches of your garden such a perfect environment for grass and other plants to thrive.