illustration of plant and soil

What’s in house plant potting mix?

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Bog standard house plant potting mix is almost always peat-based, with a bit of lime chucked in to adjust the pH, and fertiliser crystals added.

I would advise that you always bulk up the drainage of the soil with perlite, and a handful of orchid bark wouldn’t go amiss. Otherwise, when you water you’ll end up with, er, mud. Whilst this is fine if you’re happy to let it dry out, overwaterers among us end up with root rot, which is sad. Nurture should be rewarded.

I’m an underwaterer, so house plant potting mix has always been fine for me, but a couple of things have led to to pursue making my own potting mix.

I go into more detail later in the post, but there are 2 main reasons it’s a good idea to make your own potting mix:You can choose environmentally friendly ingredients

  1. A tailored potting mix can help your plant grow stronger roots.
  2. It’s much better for the environment

I’m not entirely sure if it’s cheaper to buy house plant potting mix or make you own. It probably is if you buy it in bulk, but I’m not making any promises.

Here’s a list of all the things that you may find/add to your house plant soil to help grow healthy plants:

  • peat moss
  • lime
  • fertiliser
  • perlite
  • vermiculite
  • bark
  • composted bark
  • pumice
  • coconut coir
  • activated charcoal
  • DIY fertiliser additives

Peat moss

Peat moss makes up a decent proportion of house plant potting mix, though obvs the amount varies from brand to brand.

So what is it? Well, it’s moss. From a peat bog. As it decays it becomes regular peat, and basically breaks down into soil.

Sphagnum moss is a genus of around 380 different mosses that are more commonly known as peat moss.

There’s a bit of controversy surrounding the use of peat moss in potting mix – used on its own it’s charged with breaking down too fast and compressing the roots of your plant. Mix it with perlite, however, and you’re golden.

But the real issue with sphagnum moss is the impact it’s removal from the ecosystem. The environment around peat bogs is rich, diverse, and provides a habitat that:

  1. Is pretty much exclusive to peat bogs and
  2. Takes hundreds, if not thousands, of years to form.

I plan on writing a whole article on why these ancient peat bogs must be preserved, but for now, just know that they’re one of those resources we’ll really really miss when they’re gone. If you’re interested in finding out more, check out this article.

I covered it a bit in this article about whether house plants are good for the environment

So yeah, if you can find a decent peat-free houseplant potting mix, let me know.

monstera leaf

Lime

Lime (as in limestone) is added to potting mix in order to correct the pH of the soil. Plants like to be in soil that’s got a pH of around 5.5 – 6.5 (fun fact: no one really knows why we call the acidity/alkalinity of stuff pH).

That’s the range when they can best absorb the nutrients from the soil.

monstera leaf

Fertiliser crystals

You know how you don’t usually need to fertilise plants for around the first year you have them?

That’s because the potting mix they come in in their nursery pot tends to have slow-release fertiliser crystals in them. If you can see little blue gritty bits in your soil, that’s probably fertiliser. I mean, definitely fertiliser. I think. What else would it be?

I googled what was in the blue crystals, and could only deduce that they’re made from a compound of nitrogen, phosphorus and potassium compounds. Fair enough.

Fertilisers are dyed blue so that you can see how much you’re putting on/can see if the plant already has fertiliser in the soil. Smart.

The darker blue the crystal, the more nutrients in the fertiliser.

monstera leaf

Perlite

Perlite is the white stuff that always floats to the top of your pots.

According to Wikipedia:

Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian.

And there was me assuming obsidian was black. Well. The more you know.

The reason perlite is added to house plant potting mix (I always add a load more) is that it has high permeability but doesn’t retain water – so it is great for a well-draining soil and really helps to prevent your soil from becoming too compacted.

monstera leaf

Vermiculite

According to Wikipedia, vermiculite has perfect cleavage. I have no idea what that means geologically speaking, but it made me chuckle because apparently I’m five.

Vermiculite is a type of rock, so what I’ll discuss here is how vermiculite differs from perlite, and when you’d use it.

Vermiculite is made from super-heated mica and is soft and spongy.

Perlite is made from super-heated volcanic glass, and is hard.

Whilst perlite traps water, vermiculite actually absorbs it, and can retain it for longer.

Long story short: add perlite to the potting mix for plants that suffer from root rot and for rooting cuttings (which are more susceptible to root rot. Also use perlite for plants that like to dry out quickly, like cacti and epiphytes. This is most common house plants.

Vermiculite is useful for plants that like to retain a bit of moisture, such as ferns, but I personally don’t use it, because it doesn’t aerate the soil as perlite does. Also I can’t be bothered to buy both.

monstera leaf

Bark

Orchid bark is commonly found in garden centres, but I’d encourage you to go for the bark sold in pet shops for lizard bedding – check out my resources page to see the stuff I buy.

You can get big bags of bark chips from garden centres considerably cheaper than orchid bark. I’m trying that next year, unless some comments telling me why it’s a bad idea.

Surely they’re the same, bar a bit of orchid food?

I’m all for saving a bit of cash.

monstera leaf

Composted bark

Like bark, but older. You can buy composted bark, or compost your own. Be aware that it breaks down and loses its nutritional value quickly, so you may need to add fertiliser.

monstera leaf

Pumice

Pumice adds aeration, drainage and nutrition to the soil like perlite. It’s heavier though, and doesn’t float to the top.

However, before you run off and swap your perlite for pumice, be aware that pumice, unlike perlite, isn’t sterile. God only knows what could be lurking in those porous rocks. It’s also pretty heavy.

I’m happy with perlite at the moment, but pumice could be a solution for those of you with chronic over watering problems. Pumice is more difficult to get hold of, but if you can get it, feel free to use it instead of perlite if you use my potting mix recipe below.

monstera leaf

Coconut Coir

Coir is from coconuts – the hairy outside bit all the way to the bit you can eat. The useless bit – until gardeners came along. It’s amazing:

  • Environmentally safe (we’re using coconuts flesh anyway – may as well use the bit we can’t eat)
  • Insects don’t really like it
  • Retains moisture
  • Effective growing media

It is inert though, so you’ll have to provide nutrition for your plant in other ways.

monstera leaf

Activated Charcoal

This is added to potting mixes for a variety of reasons. You don’t need it, but it has its benefits, namely that it helps prevent mould and fungus, and repels bugs. It also absorbs water, so another friend of the serial overwaterer.

monstera leaf

DIY fertiliser additives

I’m planning on using bunny poop in my house plant potting mix – it’s rich in nitrogen, doesn’t smell, and, crucially, I have a vast supply being created as I type within my home.

If you don’t have a bunny you could try worm castings, which is worm poo. Either make your own wormery or buy them from Amazon.

monstera leaf

Should you buy or make your own?

It’s really up to you.

At the moment, I buy pre-made potting mix and add my own bark and perlite. However, due to the environmental issues thrown up by peat moss, I’m going to try this year to make my own potting mix using perlite, coir, bark, and whatever else I discover. Oh, and bunny poo.

Reasons to make your own house plant potting mix

  • I’m on the fence as to whether it cheaper. It really depends how much you buy, because many of the ingredients are cheaper inf you buy in bulk. Oh, and those little coir bricks grow SO MUCH once you add water
  • Homemade potting mix is much chunkier than house plant potting mix, which encourages plants to grow thicker roots so that they can better support themselves. Finer soil mixes can lead to plants producing thinner, weaker roots
  • Chunky, homemade potting mix allows a lot of airflow around the roots, which is great for semi-epiphytic plants such as monstera.
monstera leaf

How to make house plant potting mix

Wow, I never thought I’d have a recipe blog.

You will need:

Coco coir – 4 parts. You could use sphagnum moss here, and to be honest nothing beats it for growing good roots, but we’re here for a long time, not a good time, so I prefer to use coir rather than ravage ancient peat bogs.

Bark chips – 5 parts

Perlite – 5 parts.

Activated charcoal – 1-2 parts – if you have an aquarium, you may already have some – a lot of filters use it

Worm castings – 1-2 parts. I’m going to start using one part worm castings, one part bunny poo. Anything that adds nutrients to the soil goes here. You can use compost if you like, but CHRIST you’ll get a lot of gnats.

(I got all this stuff from eBay because it’s cheaper, but if you want to get it from Amazon, there are links on my resources page).

I measure everything into a bowl or deep sided tray and mix. With my hands. Because it’s the best way.

The ratios shown above make a perfect aroid mix. For Calathea I would use 6 parts coir and 3 parts bark chips, but use your own judgement. Calathea like to have more moist soil than aroids, so the chunkier the mix, the more watering you’re going to have to do.

12 thoughts on “What’s in house plant potting mix?”

  1. I recently came across your blog and so appreciate it. Your writing style is creative and informative and I love the “er”s you put in. Feels like it’s a conversation.
    I have some Snake plants and left over cactus/succulent mix. I’m interested in the charcoal. Would you suggest putting some of that into the succulent mix for my Snake plants too?
    Thanks in advance!

  2. Thanks so much, that means a lot!

    I do put charcoal in my potting mix but I wouldn’t use it with snake plants, simply because they’re pretty disease-resilient and don’t really need it.

    If you have charcoal to use up then by all means put it in, but your snake plant probs won’t care one way or the other. You might be better if saving it for a more delicate plant.

  3. Hallo, is this good for pretty much any houseplant? I’ve a mix of cacti, succulents and actual plants and have enough to do without 14 different soils! Also, your worm cast link doesn’t work, but I found another one 🙂

    Thank you, these are very funny and interesting articles (I’m reading through a bunch)

  4. I just adjust the quantities perlite and bark to increase/decrease drainage. I use less bark for Calathea And ferns and more for epiphytes and philodendron. I do add sand to succulents, but everything else goes in broadly the same mix and I haven’t had any issues.

    You can adjust the soil mix to reflect your watering habits too – if you’re an underwaterer, adding more coir will stop your plants drying out so quickly, but use less if you’re more likely to overwater.

    Thanks for pointing out the link, I’ll change it!

  5. I love this article, I got a lot of good information from it and will use it to make my own potting mix now. But we do know why it’s called pH. It stands for potential of Hydrogen–it measures the concentration of Hydrogen ions in a substance. I learned this in nursing school. :0)

  6. Hi i have a small monstera albo (currently 5 leaves) I am so worries about it as it was rather pricey. i noticed yesterday that on one leaf it got large dark brown splodges, mainly on the white part, but my ‘investigation’ seemed to suggest over watering :(. i have cut a couple of roots off, thankfully it wasn’t too damaged re-potted into a better growing medium and not watered it. have a done the right thing? is there more i can do, or do i need to wait.

    Also it had a small infestation of spider mite that i have removed and am monitoring. Are the leaves easily damaged as it seems to get brown marks on it very easily. I feel like a terrible plant parent to this plant (please can need to point out i have lots of other plants that seem to be perfectly happy), i thought these plants were rather easy to look after but i feel mine is rather temperamental. Any help is really appreciated

  7. The white parts do brown really easily, but because they’re dark brown I suspect you’re right about the overwatering. My rule of thumb is that I don’t start to worry unless the green parts are starting to brown.

    It will take time to regrow some roots – I’d consider putting it in something that will let you easily check the roots – water, perlite, moss, or even just keeping it in potting mix but switching to a clear pot.

    They are temperamental, and slower growing that green monstera, but it should be fine. I’d recommend increasing your humidity- not only will it help your plant grow faster but it’ll discourage spider mites.

    If it makes you feel better, my Thai constellation is a nightmare. It had root rot, trapped leaves that need extracting (and now look super ragged) thrips…you name it. The thing that helped me the most was keeping it in my bathroom window. It liked the light, the humidity, and I could pick bugs off it whilst I was showering. It took a good few months to start producing healthy leaves, but I think I’m getting there!

  8. Thanks so much.
    A very small part of the green has a mark on it so thats a concern.

    I think i need to change the growing medium as i have it in soil approx 50%, perlite about 25% and bark 25%, i done that about 3 hours ago, do you think i should get it out of that and do something else?

  9. That mix is fine (monstera typically aren’t that picky, and perlite and bark will give plenty of aeration), but if the roots don’t look healthy I’d rehab them in water – wash off as much soil as you can so the roots can absorb as much oxygen as they can. Tap is fine, just let it sit for a few hours to bring the temperature to room temp.

    Keep it in water (change every 3 days or so) until it’s grown another inch or so of roots.

    If the roots look ok it’s just a waiting game. Increase light, humidity, and temperature to promote optimal growth.

  10. The roots looked reasonable to be honest, there was maybe a centimetre of one that i trimmed to be on the safe side but it wasnt mushy. ill keep an eye on it over the next day and if it looks to be deteriorating ill follow you recommendation. Thank you so much, really appreciate it

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