Choosing the right potting soil can be crucial to your plant’s growth and development. You might be confused by all kinds of soils, mixes, and different additives out there, so we will cover most of them and give you some recommendations so you can choose the best potting soil for your houseplant.
First, let’s figure out what some basic terms and factors mean when selecting the best soil for houseplants.
- Potting soil, or a potting mix – these two terms are often used interchangeably, the only difference is that potting soil sometimes contains real dirt, and potting mix never does. Potting mixes are basic substrates that serve to oxygenate and provide nutrients for plants and are typically composed of peat moss, shredded pine bark, and minerals like perlite or vermiculite. Peat moss and minerals provide aeration and are found in most of the potting mixes. The bark stops the soil from ‘slumping’ – sinking when watered.
- pH, or acidity. It is an important factor that shows how acidic or alkaline your environment is. If the soil pH is out of the recommended range, the nutrients will not be absorbed by the plant properly.
- Porosity. It is the space between soil particles. The roots’ ability to access oxygen depends on it. Porosity is increased by minerals, bark pieces, etc.
- The water-holding capacity of a plant shows whether the plant prefers a drier or more humid substrate.
- Water retention. This is a property of soil that indicates how much moisture it can hold between waterings. The plants with low water-holding capacity prefer low water retention, and plants with high water-holding capacity prefer the soil with a higher level of water retention – simple enough.
- Drainage. Good drainage means that soil will dry out at a moderate rate and will not retain too much moisture or lose all of the water too fast. It can be achieved by adding minerals, sand, orchid bark, etc.
- Aeration. Aeration shows how much airflow goes through the soil. It is linked to porosity and drainage – the more porous your soil is, the more aeration you have. To develop properly, plants’ roots need enough access to the air that goes through the soil.
There are two different types of soils: soil for indoor plants and outdoor plants. Understanding the difference between indoor and outdoor potting soil is essential for choosing the best houseplant soil.
- Outdoor soil is usually referred to as ‘garden soil’. Garden soil is supposed to be mixed with soil in the ground to improve its quality. Outdoor soil is usually dense and therefore too heavy for most houseplants. It holds too much moisture, which can cause rotting and other problems. So outdoor-plant-specific soil is not our choice for houseplants.
- Indoor potting soil is designed to have high porosity because indoor plants usually take longer to dry out between waterings and their roots need more access to the air. Therefore, soil for indoor plants contains perlite, vermiculite, moss, etc.
So, when choosing the best soil for houseplants, look for potting mixes labeled “indoor potting soil” or “well-draining houseplant soil.” As we mentioned, there is a spectrum, so you can often see mixes labeled ‘regular’ or ‘all purpose’. These mixes are suitable for both outdoor and indoor plants and are usually not plant-specific. They are light, pH neutral, pre-mixed with fertilizer, and have minerals for aeration.
You can also find out which one is better to choose soil for tomatoes in pots.
Many different soil additives affect drainage, porosity, humidity, and other things. Here is the list of the most common additives:
- Sphagnum moss and peat moss
- Coco coir
- Clay
- Minerals: perlite and vermiculite
- Sand
- Orchid bark
- Worm castings
Now we will review each one of them and explain how they improve houseplant soil quality.
Understanding Sphagnum Moss and Peat Moss for Houseplant Soil
Sphagnum Moss: Sphagnum is a genus of about 380 species of moss that grow in marshlands all over the world. Dead and dried sphagnum moss is used for growing plants. It has a great water holding capacity because of the small dense moss leaves.
Peat Moss: Harvested from the same sphagnum plant, peat moss is the layer of decayed sphagnum moss, which naturally occurs below the surface of the soil in natural peat bogs. It holds lots of moisture and enhances soil aeration and nutrient absorption. It can also affect the balance of microorganisms in the soil in a positive way.
Peat moss has a pH of around 4.0, which is pretty acidic. That is why it is often used to balance the pH levels of alkaline types of substrates such as clay. Peat moss is great for plants that prefer wet but not too damp environments.
Harvesting peat moss isn’t sustainable though, because one has to dig up the swamp in order to reach the moss, and it takes hundreds of years for the habitat to regenerate. That is why some indoor gardeners try to avoid all peat moss products and look for alternatives. One of the best alternatives is coco coir, which we will discuss down below.
Coco Coir: The Sustainable Alternative for Indoor Plant Potting Mix
Coco coir is basically the outer fiber of coconuts. Coconuts can be collected without harm to the habitat they grow in. Coconut coir provides pretty much the same benefits as peat moss. It is lightweight, which also increases airflow in the substrate, and has neutral pH, which makes it different from moss.
As a separate additive, coco coir is dried and packed into bricks. But you can also find potting mixes that contain coco coir instead of moss, making it an excellent sustainable choice for the best soil for houseplants.
Using Clay in Houseplant Potting Soil
Soil with added clay is pretty dense. It retains lots of moisture and has a high pH of about 8-10 (alkaline range). Plants develop slowly and remain compact in clay soil. Many species of grasses, petunias, and hostas prefer soil with clay mixed in.
Perlite and Vermiculite: Essential Minerals for Well-Draining Houseplant Soil
Perlite. Perlite is found in almost any potting soil for indoor plants. You can see it in the form of little white pieces. Perlite is volcanic glass collected and heated to high temperatures to make the compound more porous. Due to its porosity perlite has low water retention and is lightweight, which prevents soil compaction and sinking.
Vermiculite. Vermiculite is a naturally occurring mineral generally used as a moisture-retentive substrate. It is less porous than perlite, so it holds more water and provides less aeration for the plant roots. Despite this, vermiculite is still not too heavy for indoor plants and doesn’t retain too much water. Just like perlite, it prevents soil compaction.
If your type of plant doesn’t prefer lots of moisture and needs to dry out between waterings, you should choose perlite. That is why it is often found in succulent mixes.
If the plant prefers moist but not too soggy soil, then you should choose vermiculite for your indoor potting soil mix.
Sand as a Drainage Additive for Succulent and Cactus Soil
Sand is a soil additive that is usually put in succulent soil mixes for plants that naturally grow in sandy environments. Obviously, it is good for cactuses, succulents, and other drought-tolerant plants. Sand improves drainage and aeration. The sand alone cannot serve as a self-sufficient substrate, because it drains quickly and does not hold nutrients as moss or dirt does.
You should also avoid products labeled ‘play sand’, which are not designed for growing plants. Sandy soil is often used in commercial cacti and succulent mixes for optimal drainage.
Orchid Bark: Natural Additive for Aerated Houseplant Soil
Despite its name, orchid bark is not used just for growing orchids. It is basically dried tree bark usually collected from softwood trees: pine, cedar, or spruce. It can be used as a great soil additive for many plants. And orchids are the ones that like it indeed.
Orchid bark has all of the features that many other additives have: it helps with aeration, water flow, and soil compaction. Using too much orchid bark can make the soil dry out too quickly though. Bark has a slow decomposition rate and can serve as a cheap filler for your potting mix.
Worm Castings: Natural Fertilizer for Nutrient-Rich Houseplant Soil
Not exactly an additive. Worm castings also act as a fertilizer. Worm castings are worm feces containing some nutrients and bacteria. These microorganisms help fight plant diseases and might repel some insects; nutrients also improve the soil.
The castings, just like sand or minerals, should not be added to soil in large amounts. If you are using a soil mixture in an 8-inch pot, you can add about 8 – 16 tablespoons of worm castings – this would be more than enough.
Even though using worm castings is just as easy as using diluted fertilizers, they might not be enough for some plants. Picky species of plants may need specific fertilizers instead of just worm castings, and you should figure it out for every picky plant individually. Most of the indoor plants will accept the castings though.
Top Recommendations for the Best Houseplant Soil and Potting Mix
Best Standard All-Purpose Potting Mix for Indoor Plants
1. Miracle-Gro Premium Potting Mix (8-quart)
