What is in Potting Soil Mix?

By Ashleigh Smith

Soil is something that appears so uniform yet is made up of many different components. Each year, these different components work together with your seeds to produce your flowers, fruits, and vegetables. But what's in it? And why are there so many different mixes available?

Basic soil is a mix of sand, silt, clay, water, air, and nutrients. These components create different soil qualities based on how much each part is present. This results in differing colors, water drainage, nutrients, and compaction that affect how your plants grow. But if you have ever bought soil before, you may have noticed some mixes such as potting or bedding available to you.

What makes these so special? They utilize other materials such as perlite, vermiculite, compost, and other materials to improve your growing experience. These can help improve the retention of nutrients or water, maintain a balanced pH, and stabilize the plants without weighing them down too much (bulk density).

Perlite - A lightweight, pH-neutral granule that is used to increase porosity as it expands with water absorption. You will often see it in potting mixes ideal for cuttings or starting seeds. Its white appearance makes it often mistaken as fertilizer by those unfamiliar with its purpose.

Vermiculite - A group of hydrated laminar minerals with an accordion shape that maintains a neutral pH. Like perlite, vermiculite can increase water and nutrient retention while increasing the porosity of the soil. This allows for better drainage and root development. However, it is not as effective in this purpose as perlite, making it ideal for plants that like more water.