Potting soil, soilless mix, garden soil, topsoil and compost – all these names can easily confuse not only a beginner but an experienced gardener too. Everyone is saying to use potting mix for containers and NOT to add garden soil to pots.
But why you can’t use garden soil for potted plants? And what happens if you accidentally used garden soil in pots? In this post we will tell why you shouldn’t use garden soil to plant in containers and what to do if you are already growing plants in the pots with garden soil.
Accidentally used garden soil in pots? Do this:
If you accidentally used commercial garden soil for pots, add coarse perlite and poke around with a chopstick to get it mixed. Then, pay attention to watering. If you dug out soil from your existing garden and used it in pots, you need to repot your plant.
Tip: Commercial garden soil is not the same as the soil in your garden!
There is no doubt that the soil in your garden can be of a high quality. However, it is not the same as a store-bought garden soil. Some of them can contain perlite, compost and sand. You would need to read the label carefully before amending it.
If you accidentally used garden soil from your backyard for growing in pots, you need to repot your plant. Don’t throw the garden soil away! If it is of a good quality, you can easily amend it and turn into a good potting mix. All you need to do is mixing peat moss, perlite and garden soil.
If you already amended garden soil with compost, then you don’t need to add compost to the mix. Grab 2 gallons of perlite, 2 gallons of peat moss and mix it together with 2 gallons of garden soil. You will get your own high quality potting mix!
These are the measures to produce a bunch of potting mix which you can then store. If you need to replant just one plant, then measure how much garden soil you have and add same parts of perlite and peat moss. I just take a pot of each medium and mix them together.
What is topsoil, garden soil and potting mix?
Let’s start with the quick definitions of what is garden soil, topsoil and potting mix. A topsoil is the top 12 inches of soil removed from the ground during developmental projects. It can consist of clay, silt, sand and other organic material depending on where vendor took it from.
A garden soil is basically a topsoil which vendors enrich with compost and organic matter. Both topsoil and garden soil can be used for direct planting. Garden soil tends to be more expensive because it contains nutrients that plants can use over years.
Potting mix is sometimes also called potting soil is a medium that you should use for potted plants. It can consist of peat or coir, pine bark, and vermiculite or perlite, but doesn’t contain soil. However, you should always check the ingredients when buying a bag of potting mix.
Some bags with potting mix that have a name ‘potting soil’ on them can actually contain soil. Put it away if you want to grow plants in pots. Potting soil is suitable for raised beds or to fill empty spots in the lawn. It is easy for a new gardener to make a mistake and pick a bag with soil to use it for pots.
Why you can’t use garden soil as potting mix?
You might have noticed on the bags with commercial garden soil a note saying ‘Not for containers’. Your first thought might be that it won’t drain well in pots. And you are absolutely right. Here is the thing. When plants are growing in the ground, the soil is deep enough so that excess water can drain away from roots.
As you know, apart from water roots also need air to grow. That is not a big deal when you are growing in the raised beds, on the farm or your garden. Soil is deep enough to ensure good drainage. In a limited space like in a container you can only rely on the potting mix.
It should drain well, offer enough air, provide nutrients and hold moisture at the same time. So, why I can’t use garden soil as potting mix? Garden soil is too dense and the pot is not deep enough, so water will accumulate at the bottom of the pot. Roots that sit in the water do not get enough air and cannot grow.
Let’s have a look at this in more detail. The particles in garden soil are very close to each other. That is because it consists of small clay and silt particles. For water to drain well in the soil with small pore spaces there should be more room (several feet or more deep in the ground).
So, should I use potting mix in containers?
If there is constantly a layer of water at the bottom where roots are, they don’t get enough air. As a result, your plant won’t grow. So, what is so different about potting mix? First, as you already now, it doesn’t contain any soil. Second, it consists of mineral aggregates that form larger pores.
These mineral aggregates are perlite, vermiculite, calcined clay and sand. If you look at the ingredients list of a commercial potting mix, you will find one of these elements. Mineral aggregates form large pores in the potting mix and carry water through the medium and out the bottom.
Then, these large empty pores fill up with air and provide oxygen to the roots. Many gardeners advise to buy a potting mix with perlite or vermiculite as these are volcanic rocks that already contain air and are very lightweight.
So, if mineral aggregates are responsible for aeration, what holds the water in the mix? Organic materials like peat moss, sphagnum moss or coir. They hold on tightly to moisture that mineral aggregates want to drain away. Also, they hold on to nutrients that can wash away.
You might be thinking where plants get nutrients from because potting mix is soilless. That is why commercial mixes contain small doses of fertilizer. Don’t forget about it because many growers put additional fertilizer which can lead to plant nutrient deficiencies.
Do you buy a potting mix or make your own? Let me know in the comments section down below!
Happy Growing 🙂