While “dirt” is rarely the most glamorous part of plant care, choosing the right substrate lays the foundation for a happy houseplant. Houseplants originate from unique conditions all over the world, so your options for planting mediums go far beyond just the potting soil you would use in your garden – in fact, many houseplants thrive on soil-less mixes. Let’s dig in and learn more about how to choose the perfect mix for your plants’ root system!
Introduction to Houseplant Soils and Substrates
Words like ‘potting soil,’ ‘substrate,’ and ‘potting medium’ are often used interchangeably to talk about the material surrounding our plants’ roots. Substrate provides nutrients, holds the plant in place, and, perhaps most importantly, plays a strategic role in how much water and air is available to the roots. The right mix delivers everything your plant needs to thrive, while the wrong mix could lead your plant to accidentally dry out too fast or develop root rot from overwatering.
Ingredients for Planting Success
Most plants benefit from a mix of different substrate ingredients to create the right conditions for their root systems. Remember: potted houseplants are just a tiny microcosm of their natural ecosystem, so their needs are entirely dependent on what we provide them.
Organic materials: Bark, coconut coir, peat moss, rice hulls, compost, manure, earthworm castings, charcoal
Organic materials generally help hold onto moisture, while large additions like bark diversify soil structure and aerate the soil.
Mineral materials: Sand, perlite, vermiculite, pumice, LECA
Inorganic mineral materials aerate soil by introducing pockets of air and allowing for faster drainage so plants won’t become waterlogged.
Organic Fertilizers: Bone meal, kelp meal, fish meal
Natural fertilizers offer plants critical nutrients that support plant growth and greater resilience to stress.
You can create your own combinations with raw ingredients, but a premixed organic potting soil is a great place to start for leafy houseplants. The next section goes into specific mixes suitable for different types of plants.
How to Choose Houseplant Soil
For Aroids: Well-Draining Mix
Many popular houseplants belong to the Aracae family, also called ‘aroids’ – a group that includes pothos, monstera, philodendron, aglaonema, alocasia, and many more. These are typically tropical plants that can be grown in a well-draining potting soil. Your pre-mixed soil may include perlite (for aeration and structure) and peat moss (for moisture retention and acidity) but adding extra chunks of bark and perlite can provide airflow to these plants’ roots.
Best for: Monstera, Philodendron, Pothos, Anthurium
For Rainforest Lovers: Water-Retaining Mix
Few houseplants truly like to keep their ‘feet’ wet, but it’s a delicate balance to keep rainforest-adapted plants like ferns and African violets from drying out completely. Pre-mixed soils marketed for African violets will typically contain peat moss or coco coir mixed with perlite and vermiculite to balance moisture retention and airflow. To keep them blooming regularly, a balanced fertilizer is also beneficial. Ferns may enjoy the addition of acidic bark and a little conventional soil. Even though these plants appreciate frequent watering, they never want to remain waterlogged for long – choosing substrate with good drainage but enough organic material to hold onto moisture is critical.
Best for: Ferns, African Violets
For Desert Dwellers: Sandy Soil Mix
Succulents and cacti are adapted to drier conditions than most of the plants we keep in our homes, but that doesn’t mean they don’t need water – they just like fast-draining soil to mimic the occasional bursts of rain in their natural habitat. Garden stores like Cornell Farm sell specifically-formulated sandy, well-aerated soil mixes for succulents and cacti. If you’re mixing your own, add sand and large mineral elements like perlite, pumice, or LECA (condensed clay balls) to a lightweight soil mix. While succulents prefer a little bit of soil to retain moisture, cacti like their soil sandy and as well-draining as possible.
Best for: Cacti and succulents
For Epiphytes: Bark Mix
Epiphytic plants are adapted to cling onto trees, deriving most of their moisture from humidity and rain. These plants can be grown on bark, often sold as ‘orchid bark,’ and may benefit from sphagnum moss to retain moisture. Bromeliads and holiday cactus (Schlumbergera sp.) need fast-draining substrate but still crave a lot of water, so a mix of orchid bark, peat moss, potting soil, and an aerating mineral like perlite provides solid soil structure that can dry between frequent waterings. In general, fertilize in the spring and summer to give these flowering plants energy to sprout their impressive blooms.
Best for: Orchid, Bromeliad, Holiday Cactus
Sustainable Soils
While you should choose the substrate mix that works best for your plants’ needs, the sustainability of materials is another factor to consider for planet-friendly indoor gardening. Knowledge of these issues helps you make informed choices. Sphagnum moss and peat, for example, are largely harvested from wild sub-arctic wetlands in Canada and have a very slow rate of renewal — less than 1mm of growth per year. These ecosystems have been depleted in areas across Europe, but many North American companies try to employ sustainable harvesting practices when possible. A more renewable option is coco coir, which has a similar function in your soil but is a fast-growing byproduct of coconut cultivation. Similarly, mineral additives like perlite, vermiculite, and pumice are non-renewable mined volcanic materials that offer major benefits for soil breathability; rice hulls are an organic replacement that can serve the same function using a more renewable material.
It’s a delicate balance between function, sustainability, and availability. If sustainability issues are on your mind while choosing houseplant substrate, we recommend doing more research on your own and checking out the sustainability practices of the companies you’re buying from.
Soil Tips
- Use a moisture meter (or your finger) to gauge soil dampness between waterings
- Replace your plants’ soil every 12 - 18 months to replenish nutrients and flush minerals that may accumulate from your tap water. A great time to refresh soil is in the spring spring or any time you notice your plants getting rootbound
- If soil dries out completely, it can become so compacted and hydrophobic that water will run down the sides of the pot instead of nourishing your plant! In this case, try bottom watering – set your plant in a bowl with several inches of water and soak for 30 - 60 minutes to rewet the soil
Happy planting!
