The Truth About Potting Soils: Most Are Harmful to Your Houseplants
Julie Bawden-DavisMarch 23, 2025Spring is the ideal time to repot your houseplants. In March, April and May, they are ready to start growing rapidly. When you put them in new soil, they begin growing quickly and thrive.
Before you start repotting, however, listen up. The type of houseplant potting soil you use for your indoor garden is critical to their success. The fact is that the most important part of your houseplants is their roots. I know this isn’t the prettiest part or the part you admire, but the roots are essential. Without healthy roots, you will not have healthy houseplants.
That being said, it is vital you choose high-quality potting soil for your houseplants. But the truth is that good potting soil is hard to come by. Why? Because many soil providers cut corners by grinding up bark and trying to pass it off as “soil.” This ground-up bark is much better used as a mulch.
How to Spot Inferior Houseplant Potting Soil
It’s easy to spot such ground-up bark inferior soil when you know what to look and feel for. The soil will look like shredded bark and be very lightweight. It will also be rough, not fluffy to the touch.
To test soil before buying it, I always squeeze the bag and lift it. If it is soft and squishy to the touch and has some weight to it, the soil isn’t ground-up bark. However, if the soil is rough to the touch and feels as if it has chunks in it, and the bag is lightweight, it is ground-up bark.
Why is such ground-up bark potting soil bad for houseplants? Because it doesn’t hold water or nutrients. Both wash right through, leaving your houseplant thirsty and hungry. And what happens next? Plant failure. Big time.
What to Look for In Houseplant Potting Soil
Some top ingredients include peat moss or coir (or a combo of both). These products promote water and nutrient retention. Peat also acidifies the soil, which is good for many houseplants.
Other good ingredients to look for in potting soil include mycorrhizae, which is microscopic fungi that leads to healthy root production and nutrient and water absorption. Also look for organic nutritive ingredients like worm castings (vermicompost), bat guano, oyster shell, kelp meal and shrimp meal.
And all good potting soils have a draining and aeration agent, such as perlite or pumice. Check out my pumice product in my store.
Potting soil formulations vary. For that reason, it is best to read the package contents so that you can choose high-quality soil that fits your plants’ needs.
By now you’re probably wondering about houseplant soil brands. I only have two brands that I use on a regular basis. They are Promix BX and FoxFarm Happy Frog.
Specific Houseplant Potting Soil Mixes
For optimum growth, some houseplants require specific added ingredients in their soil. For example, if you are growing citrus indoors, you will want a potting mix that contains soil sulfur as well as the above ingredients.
Cacti and succulents also require a different potting soil than most houseplants. While there are cactus and succulent mixes on the market, I’m not always impressed with them, because they tend to be heavy on bark. This type of potting soil may provide good drainage, but it doesn’t provide high alkalinity, which cacti and succulents also need.
I make my own cactus and succulent mix by mixing 2-parts worm castings or regular compost, 1-part coarse, horticultural sand and 1-part 1/4-inch lava pebbles or pumice. The latter two ingredients provide especially sharp drainage. In 4 quarts of this mix, add 2 tablespoons dolomitic lime (to create alkaline conditions) and 1/3 cup charcoal, which will sweeten the soil and reduce odor.
When Bark is Needed in Houseplant Soil
There is one class of plants that do require a barky soil, and that’s many orchids. Because they are epiphytic (naturally growing on other plants for support with their roots exposed to the air rather than in soil) orchids should be grown in orchid bark instead of traditional potting soil. Such mixes are composed of a coarse blend of bark chips—often fir and pine.
So, there you have it. The dirt on good potting soil. If you have any questions, ask in the comments section. And if you want tutorials on repotting your houseplants this spring, including about choosing potting soil, I have an extensive Repotting Playlist on my YouTube channel.
