Indoor Potting Soil 101 & the Best Soil for Houseplants!

Are you a houseplant owner who is overwhelmed by soil choices? Sometimes getting the best soil for houseplants isn’t a matter of what brand it is—it’s about the additives you use. I’m sharing everything you need to know about houseplant soil and how to keep your plants happy and healthy.

Soil 101: Your guide to cultivating the best soil for houseplants

Hey all, this is going to be a monster of a post. And it will be all about soil! How long can I talk about soil for? A long time. I promise. But I’ll try to keep it to the basics you need to know.

Because if you’re wondering what the best soil for houseplants is…there are a few things you should know. Often store bought indoor potting soils are great right out of the bag. But sometimes you might want to throw in some more additives. 

Or you might just want to know what is in the bag you’re using! What is peat moss? How is it different from coco coir? And what about sphagnum moss? Oh God, there’s orchid bark, too? And what the hell is vermiculite?

Outdoor soil vs. indoor soil: Yes, there is a difference!

First let’s start with the basics. I’m going to separate soil into two groups: outdoor soil and indoor soil. Yes, that is a gross generalization and yes, I know it is a spectrum. But this will help us cover the basics.

Outdoor soil is, for lack of a better word, dense. It will often be labeled as “garden soil.” Garden soil is designed to be mixed with soil in the ground to improve it. Outdoor soil can also work as indoor soil if it’s designed for outdoor container gardening—but not always.

That’s why I generally buy a potting mix labeled “indoor potting soil” or “well-draining houseplant soil.” Look for those words. These are usually good to go out of the bag for houseplants because they have additives to help prevent soil compaction and facilitate aeration and drainage. 

But what makes outdoor/garden soil and indoor/container/houseplant soil different? Their ingredients. Outdoor/garden soil is way too heavy for houseplants. It retains too much moisture and is probably very dense. This can lead to root rot, among other issues.

Can I use container gardening soil for houseplants?

Indoor plants generally take much longer to dry out between waterings and require more air flow to their roots. Therefore, indoor soil mixtures designed for houseplants have certain additives in them that help address these needs. Things like perlite, moss, etc.

However, to help keep costs down for my spring houseplant repotting this year, I bought a big bag of soil designed for container gardening. I chose a high-quality soil from a local nursery (Foxfarm brand, but I’m not at all picky). 

It is actually a super light blend out of the bag with plenty of perlite already mixed in. However, for a lot of my plants, I added additional perlite and scoops of peat moss, worm castings, and occasionally orchid bark. If this sounds overwhelming—it isn’t. They all just contribute to drainage and air flow, and I learned literally through trial and error.

Let’s talk about the best houseplant soil additives

I’ve mentioned a few soil additives already, so let’s talk about them in more detail. You will start seeing words like “sphagnum moss” and “perlite” mentioned when reading my and other plant care guides. You’ll also see them mentioned in houseplant hobbyist forums and groups.

Big disclaimer here: I know houseplant people can have a lot of opinions on things. This is just what I use and what I’ve found works. Experimentation is great. If I’ve omitted something you love, it just means I haven’t personally used it so I can’t speak to it. No shade. 

ADDITIVE #1: SPHAGNUM MOSS

Sphagnum is a genus of mosses with hundreds of species. But I’m not going to get too far into sphagnum as a genus because as a soil additive, you’re dealing with the dead kind. 🙂

Alive, it grows in wet climates like the surface of swamps or bogs. It can be sustainably harvested because it will regrow without problems. Dried, it makes a wonderful additive or substrate for growing plants! I have a whole post on how to root plants in sphagnum moss.

Sphagnum moss vs. peat moss

But what about peat moss? Is it the same or different? Well, it’s actually from the same plant, it’s just a different part. I read on this brand’s website that it is the layer of decaying, water-saturated sphagnum below the surface. It has a finer texture.

However, despite its popularity, harvesting it isn’t sustainable. That’s because you have to dig up the swamp to get to it, and it can take hundreds of years for the habitat to regrow, regenerating at the agonizingly slow rate of 1 mm per year. 

I didn’t realize peat moss was environmentally problematic until very recently, so you’ll see it recommended as an additive in a lot of my posts. However, I am trying to move away from using peat moss, especially as an additive I keep a bag of at home. Know better, do better, right? 

What is peat moss used for?

I want to talk about what peat moss is actually used for before we move to another additive, which is a great alternative to peat moss. What is peat moss used for, and why is such a popular material to mix with soil?

Well, it retains a lot of moisture while remaining light. That means that it helps facilitate good drainage and is great for plants that like damp but not soggy soil. Peat moss is also physically light and a bit fluffy when it is dry. 

That means it helps prevent soil compaction and encourages good aeration and air flow to a potted plant’s roots. So it’s kind of a bummer to have to stop using it, right? Well, not necessarily! Let me tell you about its cooler and more sustainable friend coco coir. 

ADDITIVE #2: COCO COIR

Coco coir is fiber from the outer husk of coconuts. It’s what your doormat is probably made out of 🙂 It has tons of uses and is sustainable because it comes from coconuts. Which don’t take hundreds of years to regenerate. 

Peat moss vs. coco coir

Coco coir is a good alternative to peat moss because it provides many of the same benefits. It’s lightweight, even used in upholstery padding and mattresses. Because of this, it also increases air flow in the soil.

Also like peat moss, coco coir retains water without becoming too heavy. As a soil additive, it generally is harvested, dried, and packed into bricks. You can then crumble the coco coir off of the bricks and mix it in with your soil. 

Bonus points if you can find an indoor potting soil that uses coco coir instead of peat moss. I know most of the pre-mixed soils I see around here use peat moss. (Which is fine for your plants! Just iffy on the sustainability issues.)

ADDITIVE #3: PERLITE

Perlite is probably already in any indoor potting soil mix you’ll buy. It’s the little white bits that look like rocks but are really lightweight. And that’s why perlite is so fab!

Perlite itself is an amorphous volcanic glass that occurs naturally, which sounds very much like something you wouldn’t put in soil. But it is! And it’s great. It’s also used for a ton of things including construction, biotechnology, and beer making. 

What is perlite used for?

Perlite’s lightweight nature helps prevent soil compaction and generally loosens things up. It also has low water retention, helping water flow freely through soil and preventing overwatering. I like mixing perlite and damp sphagnum moss to root cuttings in my DIY propagation box.

ADDITIVE #4: VERMICULITE

Vermiculite is a hydrous phyllosilicate mineral which, I’m going to be totally honest, I have no idea what that is. But basically it’s a naturally occurring mineral used as a moisture-retentive medium for growing plants.

It does all the good stuff: help encourage good drainage, retains water without being too heavy, prevents soil compaction, etc. I do want to flag that some people have some health and safety concerns over vermiculite, but it’s generally not an issue at all as a soil amendment.

What is the difference between perlite and vermiculite?

Perlite is excellent for drainage. Therefore, you can often find it in soils that are great for plants that need to dry out between waterings. You’ll also usually find it alongside soil and sand in succulent soil.

Vermiculite, on the other hand, helps the soil retain water. Like peat moss and coco coir, it retains water without being too heavy. This is a great option for plants that like to be moist but not sopping wet.

ADDITIVE #4: ORCHID BARK

Orchid bark isn’t just for orchids—though orchids do love it! It’s just tree bark that comes in dried shavings and chunks. It’s a nice soil amendment for many plants.

I am starting to feel like a broken record when I say the additives help with aeration, soil compaction, and water flow. LOL. But that’s what orchid bark does. 

I personally am not a huge fan of orchid bark, so I do throw some into my bigger potted plants to help with aeration. Aroids (plants in the araceae family) generally like it. When I recently repotted my monstera deliciosa with a jute pole, I threw in a couple handfuls of orchid bark.

I find that using too much orchid bark can make the soil dry out too fast. When I repotted my heart-leaf philodendrons this spring, I included orchid bark. That was a mistake. 

They dried out too fast and actually ended up looking rather sad. Once I repotted with fresh soil and no orchid bark added in, they perked right up.

ADDITIVE #5: SAND

Sand is another soil additive that is commonly found in succulent soil mixtures. It’s great for cactuses, succulents, and some other drought-tolerant plants that do well in hardy soils. (See my post on how to make your own succulent soil.)

Sand helps with aeration and drainage, and it helps mimic the natural desert environment and its sandy soil. However, make sure to avoid things like play sand, which can actually compact in the soil and defeat the purpose.

ADDITIVE #5: Worm castings & how to use worm castings in potted plants

Worm castings are worm poop. Yum. Here’s how it works: Worms eat waste, worms digest and poop out glorious castings that are chocked full of good bacteria and nutrients. You can buy it by the bag.

Benefits of worm castings in houseplant soil

Diluted houseplant fertilizers are pretty easy to use, but I don’t like having to worry about another thing. Worm castings won’t burn your plant’s roots and lead to damage. And the good stuff they bring with them helps the soil too, not just the plant.

I’ve read that they help protect the plant from pest issues, but I’m not sure how true that is. If so, great! If not, still great, because worm castings are easy to use. I just throw some in to my soil mixture before I pot the plant up. I don’t measure.

Disadvantages worm castings in houseplant soil

You don’t want to do like, a 50/50 ratio of worm castings to soil. I just said I didn’t measure, but to give you an idea of how I ballpark it—if I am repotting a plant with a soil mixture in an 8-inch pot, I’d probably mix in about a handful or two of worm castings.

Worm castings are also not enough for some plants. BUT. They have seemed to be more than enough for all of my houseplants! If you have a picky plant, you may need to supplement with a special tailored fertilizer. (Like African Violets, for example. I don’t have any of those.)

Other houseplant soil issues explained

I’ve gone over 5 of my favorite soil additives to create the best soil for houseplants, including what they are and why I like to use them. Now I want to touch on a few other houseplant soil issues that I have experiences.

White fungus in houseplant soil

If you notice a white powdery looking mold growing along the soil line of your plant, it’s almost certainly saprophytic fungus. This will not hard the plant, but it’s possible that the underlying cause of the white fungus could be problematic.

Saprophytic fungus feeds on decomposing stuff in damp soil. There is so much stuff living in your soil that it’s entirely possible the fungus exists but only shows itself when you overwater your plant. That’s because saprophytic fungus feeds only on wet soil.

If you’d like to get rid of it, simply scrap it off the top of the soil, chuck it, and aerate the top layer of soil a bit using a fork or chopsticks. This will help increase air flow. If the plant will tolerate it, let the soil dry out before watering it again.

Giving your plant more like will also help nuke the white mold since it helps dry the soil out faster. If the problem is persistent, repot the plant using fresh, high-quality soil. Clean the pot thoroughly before repotting the plant and do not reuse the old soil. (That’s always a good rule though!)

Yellow mold in houseplant soil

Yellow mold bothers me way more than the white mold does. This kind of mold has kind of a slimy look to it with small bright yellow “balls” in it. Ugh. I’ve read it’s also a kind of saprophytic fungus that feeds on un-decomposed material.

While it looks gross, it isn’t harmful to the plant. However, much like the white fungus, it could indicate you are overwatering or not letting the soil dry out enough between waterings. I have experienced this type of yellow mold in some of my lower light plants, specifically a snake plant I had in Ramona’s room.

I simply scooped the spot out, trashed it, aerated the top layer of the soil with a fork, and let the soil dry out. When I eventually repotted the plant, I threw the old soil out and repotted with fresh soil.

Mushrooms growing in houseplant soil

Occasionally you might even get cute little mushrooms growing in your houseplant soil. It might be startling the first time you see it, but remember—mushrooms are just fungus. They don’t hurt the plant. I saw a bunch of little cuties in some rhaphidophora hayi plants at Lowe’s recently.

Simply pluck the mushrooms out and throw them away. DON’T EAT THEM! Since the mushrooms need damper-than-normal conditions to sprout, aerate the top of the soil using a fork or something similar. Then let it dry out.

Consider reassessing your watering routine to ensure you don’t start a mushroom village again. It’s usually a sign that the soil is remaining too damp. When you eventually repot the plant, throw the soil away and use new soil.

Speaking of…can I reuse soil for houseplants?

I mean, I have told you guys like 100 times to throw out old houseplant soil. Theoretically you could sterilize it and reuse it, but why risk it? Throw the old soil away and repot your plant with fresh soil.

Besides, it’s likely that any fertilizer that came in your soil is long gone by now, so giving it the fresh stuff will make it happy!

Pin my indoor potting soil 101 post about the best soil for houseplants!