Everything You Need To Know About House Plant Substrate/Soil/Potting Mix

New houseplant people, listen up:

• Soil is not anywhere near as important as getting the light/water correct
• Those pre-made species-specific potting mixes MIGHT work for you, but they might not
• Keep things simple
• When people refer to a ‘chunky’ soil mix, they’re talking about orchid bark/leca/pumice

What I keep in my soil ingredients arsenal

• Store-bought houseplant potting mix
• Perlite
• LECA
• Orchid bark

I have dabbled with worm castings and charcoal in the past. I personally think charcoal is a waste of time, but worm castings are great for adding nutrition. I have LOADS of coir but switched to using just store bought soil because… I’m lazy.

Any houseplant potting mix is fine. Don’t buy anything for outside plants for two reasons:

1. It tends to stay too wet for too long
2. There’s often compost/manure in them that can attract flies

The soil by itself is usually too dense and retains too much water. I add leca, perlite or orchid bark to increase the airflow.

Why not just use houseplant soil on its own?

It’s too dense. This is bad for two reasons:

1. The soil stays wet for two long
2. There isn’t enough airflow

Roots need oxygen. If your plant is in soil it will have soil roots, which can absorb oxygen from the air (like we can). If the soil is staying too wet for too long and there are no chunks to create air pockets, the roots will rot.

If your plant is established in water, it will have water roots, which can absorb oxygen from water (like a fish). Like soil, water can get deoxygenated and can also cause rot.

I do think houseplant soil is getting better, BUT it’s still cheaper to cut it with leca/perlite.

My soil recipe

You won’t go far wrong with equal parts houseplant potting mix, perlite and/or orchid bark and/or leca.

I don’t use an exact recipe. I don’t even usually mix it, I just add different ingredients in layers and then hope it mixes itself over time.

All of the quantities are determined by how much I have of any one ingredient at the time. If I find it dries out too quickly (within a couple of days, depending on season), I add more soil. If it stays wet for too long (three weeks) then I’ll add more bark/perlite.

A more ‘traditional’ houseplant soil recipe is this one, which I used to use, but don’t feel is worth the hassle:

• 5 parts coir (soak it in water then squeeze out the excess)
• 3 parts perlite
• 3 parts orchid bark
• 1 part charcoal
• 1 part worm castings

Why I don’t buy fancy plant-specific soil mixes

I don’t like these mixes, not because they’re bad, but because they’re pushing a false narrative that certain plants need specific soil mixes.

If a new plant person has an Alocasia and they put it in a soil formulated for Alocasia they mentally tick the soil box. They KNOW the plant has the right soil – it says it on the label.

But it might not suit their needs/conditions. The people who make it are making something that suits their environment. Also, they know what they’re doing.

I like the Grow Tropicals Philodendron mix because it suits my plants, care type and home environment. I don’t buy it often because it’s cheaper for me to buy houseplant mix and cut it with orchid bark and perlite. And I certainly don’t keep it for my philodendrons.

It doesn’t make enough difference to be worth the price.

It’s nice, and it’s convenient but it is NOT necessary.

How bad is the soil that comes with the plant?

Either I’ve been very lucky or it’s not as bad a people make out. I rarely repot my plants straight away and if i do I usually incorporate the old soil into the new.

My hoya bella still has a ‘plug of death’ and it grows fine. Obviously your mileage might vary but I’ve bought literally hundreds of plants and I’ve NEVER bought a plant with soil so bad i had to repot it from a nursery.

I have been given plants by friends to revive and it’s almost always in outside potting soil. Those i will repot, but tbh they’re usually so far gone I chop and prop.

Reusing soil

As I said, all my plants go into a weird frankenstein of whatever ingredients I have. I also rarely throw out soil (because wasteful) and I get surprises like this:

Yes, that is a Calathea growing in a Philodendron brasil pot.

People worry about pests in the soil but the pests I don’t want to get (mealybugs, thrips, spider mites) don’t live in the soil. Gnats are a result of providing them with a gnat-friendly environment (and as an underwater I do NOT do that).

If you don’t want to reuse soil, don’t, but I do and it’s fine.

How to tailor soil to particular plants

By and large, most houseplants will be totally fine in a very similar soil mix.

You don’t need to tailor soil to plants because you should be tailoring the light and water to the plant.

For example, Calathea need less light than hoya and like to stay consistently moist. A hoya in a bright window will dry out faster than the Calathea in a darker spot because it’s hotter and drier.

After a week or two, the Hoya might be bone dry and ready for watering. The Calathea (in the same soil) won’t be as dry but would still appreciate some water because they prefer to stay damper.

If you’re an underwaterer, add more water retentive ingredients to your soil, such as leca.

Overwaterers add more bark.

Do NOT try to replicate what is happening in the wild, substrate wise. Plants grow in a variety of substrates and conditions and appealing to nature in this way is a waste of time. Alocasia can grow in water in the wild, but they rot in the blink of an eye in hydroponics unless you’re on the more experienced side.

The only exception I have to this rule is:

• My maidenhair fern don’t get any bark or leca – they’re in perlite mixed with soil
• My orchid is kept bare root
• Succulents/cacti for most people – I keep them in the same soil but I also whack them outside at any opportunity. They need the brightest light you can offer, lots of water frequently but then dry out SUPER quickly. Professional cactus growers water daily but dry out the soil with a hair dryer.

In conclusion

Soil isn’t that big a deal IF you have the light and watering needs down. If you don’t have the light and watering needs covered, the best soil in the world won’t help.