If you’re growing in containers, chances are good you’re using some kind of potting soil for your precious plants.
But what if I told you that the “soil” in your pot isn’t technically “soil” at all? What if I told you that it’s a mix made of composted tree materials, peat moss, and a myriad of other ingredients?
Well, it’s true. Potting soil is a man-made creation that is in some ways superior to normal garden soil when it comes to growing plants in containers or pots.
In this article, you’ll learn exactly what potting soil is, what makes good potting soil and recommendations for different types of plants.
What’s In Potting Soil?
Standard potting soil is generally comprised of three things:
Composted tree bark
Sphagnum peat moss
Vermiculite or perlite
While there can be many more ingredients, these are the base three that make up the bulk of most potting mixes.
These three ingredients are meant to hold nutrients and moisture while still giving your plants plenty of air.
What Makes a Good Potting Soil?
The simplest definition of good potting soil is this:
The best potting soil is one that offers the perfect amount of stability, nutrients, moisture, and air.
Let’s go over each of these, one by one.
Nutrients
Quality potting soil will contain all of the nutrients that your plants need to thrive. They will include humus, finished compost, and / or gypsum and other ingredients to ensure optimal nutrition.
Aeration
High quality potting soil will be light, fluffy, and not compact easily. It will allow the roots to access air and oxygen so they can develop optimally.
Moisture Retention
While aeration is important, the best potting soil must balance aeration with water retention. They need to drain well to avoid mold or rot, but hold on to some moisture so your plant’s roots can drink.
Structure
Good potting soil will have a consistency that makes it easy for plants to anchor their roots. It provides stability for a plant’s root system, preventing them from falling over or being torn out by the wind.
Weight vs. Quality
It’s important to understand that the quality of your potting soil is not directly related to its weight.
It’s easy to mistakenly assume that the heavier your potting soil is, the better it will be for your garden. In actuality, potting soil only ever becomes heavy due to two reasons: it is very wet, or it has lots of sand in it. Some companies also add in normal dirt or sedge peat, weighing the mix down.
None of these things are good, and it is best to avoid them.
Mold or Fungal Growth
Potting soils available for sale at garden centers are almost always sterilized and treated, meaning they should be free of mold or fungal issues. But once you open up the bag, you’re exposing it to mold, fungus, and mildew.
Generally speaking, light mildew, fungi, and mold are not big issues. They usually will be dried up by the sun without ever causing any harm to your plants, and they are simply a sign that your soil might be too moist.
If you do want to prevent them from growing, though, simply spread out your potting soil on a sheet and let it dry in the sun for a few days before use.
Fertilizer Types: Slow Release vs. Starter
When you look at all the different types of potting soil available, you will most likely notice that many of them will mention fertilizer and use phrases such as “starter charge” and “slow release.”
Starter Charge
If a potting soil says that it has a “starter charge” of fertilizer, this simply means that it contains enough fertilizer to last your plant through the first few times it is watered. You will still most likely need to add your own fertilizer to the soil, but the starter charge at least helps your plants to get through the initial stages of their growth.
Slow Release
If a potting soil says that it has “slow release” fertilizer, this means that it contains slightly more fertilizer, but only enough for approximately a month.
Again, you will have to eventually add your own fertilizer, but slow release will last for at least a few weeks.
Maintaining Moisture
In addition to fertilizer, many potting soils will also contain added chemicals or ingredients that are meant to help retain moisture. This is a great feature, and it allows you to water your plants a little less often than normal.
You still will need to keep an eye on everything and make sure that you do not leave your garden for too long, but it does give you some breathing space.
An important thing to keep in mind with potting soil that has water retaining features is that you must avoid overwatering. Because the soil holds more water than normal, you will have to make sure that your normal watering patterns do not leave it too saturated.
Mulch, Manure, & Garden Soil
A question often asked by new gardeners is:
“Can I use mulch, garden soils, or manure as a replacement for potting soil?”
The short answer to this question is no.
Garden soil is basically potting soil, but it is made up of worse materials like sand, unfinished compost, and heavier materials.
Mulch is composed entirely of raw wood products, and is meant to be placed on top of soil in order to prevent the evaporation of water. This does not work well with flower pots, and is better suited in outdoor gardens and landscaping.
Manure also does not work well as a base mix for potted plants. It contains high amounts of nitrogen, and should be mixed into soil to prevent it from being too concentrated. This product is better suited for outside gardens as well.
Potting soil, on the other hand, can be used for both flowers and vegetables, and it almost never runs the risk of harming a certain type of plant.
Special Potting Soil Mixes
While the basic mixture of pine bark, peat moss, and either perlite or vermiculite is sufficient for many people, there are two common situations where you might require a different mix.
Orchids
Orchids require a large amount of drainage, meaning that regular potting soils are generally too heavy for them. If you plan on growing orchids, make sure to look for a specialty potting mix that is specifically meant for this flower.
Cacti and Succulents
Cacti and succulents require soil with increased drainage. You can either look for a potting soil that is meant for these plants, or you can make a mixture of 50% regular potting soil and 50% sand.
Mixing or Making Your Own Potting Soil
Everyone likes to do things differently, and some people find that it works best when they add certain additional ingredients to their potting soil.
Plants are generally forgiving as long as they receive the right amount of water, so feel free to experiment with adding things such as plant clippings, sand, clay, and different types and amounts of fertilizer.
If you start to run out of one type of potting soil and would like to switch to another, it is also possible to mix them. Make sure that you blend them together as much as possible, and simply use your new creation as you normally would.
Make sure to comment below and tell us your favorite type of potting soil to use, and feel free to ask us any questions you might have!