The Real Dirt on Potting Soil

Posted by on Jun 10, 2014 in Gardening | Comments


When I first started gardening, I assumed that soil is soil, and you can use any type for any need. Oh, how wrong I was. I had no idea that you couldn’t succeed at growing plants in containers using soil from the garden. I knew that potting soil existed but had no idea of its importance until I failed at container gardening too many times. If you, too, have failed at growing plants in pots, your soil might just be to blame, and you need this article just as much as I did.

tomato seedling

For starters, let’s go over the different types of soil you’ll find at the garden center, then we’ll jump right into the specifics of potting soil.

Garden soil

This is the soil in your garden, or at the store. It’s soil that’s specially formulated to be used in the garden for growing vegetables, herbs and other plants. It has the necessary nutrients for plants to thrive on.

Topsoil

This is the top layer of soil. It can be harvested and bagged up from any site and there’s no guarantee as to what’s inside. Topsoil is usually bagged up with no consideration as to nutrients, so it’s not recommended for use in the garden. Topsoil is generally used to mix with existing soil in the yard for landscaping.

Compost

Compost is made from decomposing organic waste, such as leaves, yard waste, kitchen scraps or wood chips. It is used to improve the nutrient quality of your soil.

Manure

Manure is animal feces or decomposed plants. When aged, manure is used like compost, to enrich the soil in your garden or containers to improve plant growth.

colorful leaves

Potting mix

Potting mix is simply a medium in which to grow plants in containers. It’s special because it contains the perfect mix of ingredients to both hold and drain water while feeding plants. It can contain soil or be soil-less. When it is purchased commercially, it is sterilized to ensure it’s free of fungus and weed seeds.

The components of potting mix:

  • Peat: Decomposed sphagnum moss, used for it’s ability to retain water.
  • Perlite: Highly porous volcanic glass. Aides in aeration of the soil. This is the white Styrofoam-ball-looking things you’ll see in potting mix. It allows water to drain quickly from the pot.
  • Vermiculite: Made from mica, acts a sponge to soak up water, will hold more water than perlite and is great for very thirsty plants, as it creates a potting mix that retains water.
  • Composted tree bark: Provides organic matter for plant nutrients and aeration for the soil.

There are more than 15 types of potting soil at our local garden center, and all of them are different. Some contain various fertilizers to guarantee great crops, some include sand to keep plants from blowing over in the wind, some contain chemicals to keep away weeds, fungus, bacteria and insects, and others contain more filler than nutrients. They can be basic and they can be complicated. When in doubt, go basic. You can always add things later on if you feel the need. I recommend Dr. Earth brand organic potting soil. They are chock-full of organic nutrients and we’ve yet to see a plant fail to thrive in their soil.

Why can’t I use garden soil in containers?

Garden soil tends to contain too much clay to be used in pots. Excess clay prevents rapid drainage and aeration of the soil, two essential characteristics of a good potting soil. Some people do find success with making potting mix with their garden soil by adding perlite and compost, but it won’t work on its own.

You might be thinking: “but it drains perfectly fine in the ground, why wouldn’t it in pots?”

In the ground, soil can drain horizontally as well as into the depths of the ground. There is really no limit to where the water can spread. In pots, with clay-based soil, the water moves very slowly through the pot and collects in the bottom while it slowly drains, leading to all sorts of troubles with rot, fungus and bacteria in your soil. The heavy soil also doesn’t allow roots to easily grow and spread, which will inhibit growth.

Mixing potting soil in a bucket

Why make your own potting soil?

There are two good reasons to make your own potting soil. The first is to save money. If you need large amounts of potting soil, making your own can save you money. High quality organic potting soil is very expensive. If you only need to fill a few small pots, by all means, invest in the good stuff. However, if you’re looking to fill a whole container garden, homemade might be the way to go.

The second good reason is to have control over the ingredients. Making your own potting soil mix means you can customize it to the specific needs of your plants. If you’re growing heavy feeders like tomatoes, you can add in a handful of slow-release fertilizer. If you’re growing cactus, you can be sure to add more perlite to allow for quick drainage. This element of control is also great for keeping your soil free of chemicals like pesticides and fungicides that you may not want there.

The fact is, when you buy potting mix from the store, you never really know what’s in it. Not all potting mixes are created equal, some are incredible, and some are so full of filler you wonder how they can get away with claiming you can grow plants in it. Unfortunately the only real way to know if a mix is good is to try it, or take someone’s word for it. It’s a sad thing indeed when the end of the growing season comes and you realize the reason you have no tomatoes to eat is because you bought the wrong potting soil.

If you make your own potting soil, you get to take one more step toward taking complete control of your garden.

How to make your own potting soil

Mix up all the ingredients in a bucket, garbage can, or bin. Using a receptacle with a fitted lid is helpful to save soil for future projects. If you’re anything like us, you can never have enough potting soil! Be sure to wear a dust mask so you don’t inhale the particles.

The following is a very basic recipe for potting mix. It can be used for a variety of vegetables, herbs and decorative plants. You can also dress it up with your favorite fertilizer!

Basic potting mix:

  • 1 part peat
  • 1 part vermiculite or perlite
  • 1 part compost

Tip: If your peat moss is dry when you get it, be sure to soak it for a few hours before mixing your soil.

Choosing or making the right type of soil for your gardening project is essential to its success. Good soil grows strong plants and when you’re growing plants in containers, it’s especially important to use the proper medium. Whether you choose to buy or make your soil, you’re now equipped with the knowledge to do it right the first time.

Good luck and good gardening!

What’s your go-to formula for potting soil?

Comments