Topsoil vs potting soil, which one do you use, and when, and can you use them interchangeably? And what is the difference between topsoil and potting soil? Those are questions every beginner gardener asks themselves. To answer those questions, we need to learn the functions of the three soil types.
In this article, we will discuss the difference between the two common soil types and how they function.
Topsoil vs Potting Soil
First, let’s discuss the appropriate uses for topsoil vs potting soil.
Top soil is for garden beds and landscaping and improves overall soil quality because of its nutrient richness. It makes up for the upper layers of soil and is the most fertile part of a garden bed’s soil.
Additionally, when gardeners use top soil, they mix it with the preexisting dirt and earth at the planting location. Despite its fertility and nutrients, those aspects can dissipate quickly. This type of soil is unsuitable for sowing and germinating seeds, as this process requires a certain amount of moisture and oxygen that top soil cannot provide.
Potting soil’s sole purpose is for growing plants in pots or containers, and it helps plants maintain moisture around their roots. And unlike top soil, it also does not compact. Instead, it allows plants to receive proper drainage growing in the confinement of a pot. Potting soil also goes through a sterilization process to help prevent fungal growth, other harmful organisms, and weeds. 
Now, let us discuss the contents of each soil mixture and how they benefit the plants growing in them.
Top soil typically comprises of clay, sand, humus, and slit. Humus is microscopic fragments of dead bugs, decayed plants, and old leaves, and these pieces of organic matter offer a significant amount of nutrients to the plants growing in top soil. Some of those nutrients include phosphorus, potassium, magnesium, and calcium. Despite topsoil having a high nutrient profile, fertilizer is still necessary in many cases. And that is because of topsoil’s fast nutrient depletion, and it may not offer everything a plant needs.
Potting soil mixtures typically comprise of bark, peat moss, and perlite. That means that potting soil is actually soilless. Perlite is the small white pellet-like fragments you see in potting mixtures; they are made from volcanic glass and prevent the soilless mix from becoming dense. Because potting soil delivers little to no nutrients due to its lack of humus and minerals, amendments and fertilizer are beneficial in many situations.
The differences between topsoil vs potting soil comes down to what their contents are and their uses. And we must mention that you should not use the two soil types interchangeably, as each serves a unique purpose.
Frequently Asked Questions
Can I mix topsoil and potting soil?
You can mix potting soil and topsoil to save money. But for forewarning, using any amount of topsoil in container planting can cause too much moisture retention. It is best to mix topsoil with potting soil for container plants that require heavy amounts of moisture or need support from a denser base.
What is better potting soil or topsoil?
You cannot compare potting soil vs topsoil. Firstly, topsoil is for garden beds and landscaping to improve pre existing soil quality. And it is dense and does not perform well for planting in containers. Secondly, potting soil mixtures are for growing plants in containers and offer a free-flowing dirtless substrate containing peat moss, perlite, and bark.
How do you turn topsoil into potting soil?
You can turn topsoil into potting soil by adding the proper soil amendments. Adding one part peat moss and one part perlite pellets to your topsoil mixture will help prevent it from becoming too dense, and it allows for the proper drainage that container plants need and traditional potting soil offers.
Is garden soil and topsoil the same thing?
Garden soil is essentially topsoil that has more soil amendments, including bark, peat moss, compost, fertilizer, and or shredding. Essentially, it is for garden beds with plants that need even more nutrients than topsoil can offer.
Wikimedia Foundation. (2022, November 11). Potting soil. Wikipedia. Retrieved November 13, 2022, from https://en.wikipedia.org/wiki/Potting_soil#Sterilization