How to Make A Terrarium

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Terrariums are as hard or easy as you make them.

The first tip I’m going to give is to NOT look up terrariums on Pinterest. They look beautiful but aren’t functional.

A frighteningly large number of the pins show succulents in terrariums, and whilst it’s not impossible to keep, e.g. a jade plant in a terrarium, it’s a bit like trying to keep your cat in a fish tank.

You CAN do it, but you’ll have a really unnecessary uphill battle that neither you nor the cat will enjoy.

What should you put your terrarium in?

I favour a large terrarium because you can create great humidity without needing a humidifier, and if you have great humidity, you can grow plants really quickly.

If anyone here is into tropical fish, you’ll know that bigger is always better when it comes to tank size, and the bigger it is, the easier it is to keep everything stable. Unlike fish, you can cram a tonne of plants in and they won’t start eating each other.

Anything glass will do. It doesn’t even need to be glass if you have a grow light, but it rather begs the question why bother if you can’t actually see it.

My current terrarium is HUGE:

As you can probably tell, it’s an old aquarium. The lid is a piece of plastic with the light and fan attached.

You can score old aquariums pretty cheaply off Facebook marketplace, and since it doesn’t need to hold water it doesn’t matter so much if they have chips and nicks.

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How to make a terrarium in a glass jar

…Or you can make a tiny terrarium.

Get yourself a glass receptacle (preferably with a lid to keep the humidity in) and a small plant – a single fittonia is perfect for a small terrarium.

I like to line the bottom with a layer of leca, then some filter fleece stuff (this just stops the soil leaking into the leca, and helps to stop the soil from being waterlogged), and then soil mixed with a bit of charcoal or carbon. Add your plant and you’re done!

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How to make a closed terrarium

There’s a lot of buzz around those sealed terrariums that last for years and years without anyone opening them, and that’s simply because they’re incredibly cool. Buuuut they’re not that practical.

Sure, you don’t need to water them BUT they become very overgrown very quickly, and once they become overgrown they’re hard to stop from rotting – if the glass has condensation on it (which it will) and then the leaves touch the glass…the leaves will end up rotting.

Also, airflow is very important to stopping plants from rotting. A sealed terrarium doesn’t have any airflow, meaning that you need to be pretty careful about getting the right balance of water, oxygen and bacteria.

Sealed terrariums ARE a thing, but it’d take EITHER a very skilled plant person to make one that worked OR one amateur a dozen or more attempts.

You need to ensure that the plants are releasing enough oxygen to sustain the bacteria in the soil that can convert dead plant matter into nutrients that the plants can absorb.

WAIT

Does this mean that sealed terrariums are basically structured so that a plant cannibalises itself? Horrifying, in a quiet sort of way.

A closed terrarium is a nice alternative. The lid ensures that humidity stays in, so you shouldn’t need to water that often (I have an article on how to water a terrarium here) but you can trim plants and remove any sludgy matter as and when you need to.

Again, bigger is better, because you don’t need to prune as often. If you like pruning your plants, grab yourself a mason jar and crack on.

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How to make a large terrarium

Step 1: get yourself a tank:

I used an aquarium because we’ve just moved and we need to do a LOT of renovation. It just doesn’t make sense to have a massive box of fish to move around (don’t worry, the fish have gone to a friend just up the road with a big fish room so we can go and visit them whenever we like).

You can buy ‘proper’ terrariums but they’re EXTREMELY pricey, so an aquarium might be a cheaper option.

Step 2: add a drainage layer

Obvs there are no drainage holes in a terrarium, so we need something to stop the bottom of the tank from getting all muddy and gross.

But Caroline, I hear you cry, why is it ok to add rocks to the bottom of this, but it’ll kill a house plant?

  1. It’s glass, so you can see the water line
  2. You don’t water terrariums the same way as you would a normal plant, so you’re less likely to end up with a reservoir at the bottom.

terrarium drainage layer

I like to use leca for this, because it absorbs water. That’s beneficial for a couple of reasons:

  1. the leca soaks up any standing water on the bottom of the tank, preventing it from getting all stagnant and gross
  2. the water within the leca will gradually evaporate, increasing the humidity in the terrarium

You can 100% use regular gravel. That’s what most people recommend. I use leca because we have a frog in the terrarium that NEEDS extremely high humidity to survive so we do everything we can to do that naturally so we don’t need to rely on things like foggers.

I wouldn’t recommend going outside and grabbing some gravel from your drive, but if you do do that, WASH IT THOROUGHLY. BOIL IT. SET IT ON FIRE (obvs jokes re. the fire, but please, please wash it.

If you do decide to add leca, you’ll need to wash it first. If you have washed leca, give it a soak. Terrariums rely on humidity, and if you dampen everything BEFORE you add in plants, it won’t take as long to get the humidity up.

Step 3: add a membrane

This is a step that is definitely optional but if you DON’T do it, you’ll probably regret it.

We add a layer of filter membrane – it’s this fleecy stuff you put in aquarium filters. You can get it on Amazon.

It doesn’t look great tbh:

You might be asking ‘well, if it looks crap and it’s not necessary, why bother?’

The purpose of the membrane is to stop the substrate from falling into the leca. Once the leca is full of soil it’ll look gross and you could potentially get grim muddy water if you overwater.

It’s one of those things that is NOT a big deal until one day you think ‘I wish the drainage layer wasn’t full of dirt’.

Put in a membrane. Get a black one if it makes you feel better.

Step 4: add substrate

You can buy terrarium substrate. It’s pretty good. There’s no reason to make your own if you don’t want to.

I recommend adding a layer of charcoal before soil if your terrarium soil doesn’t have any in it, though most of the ones I’ve seen already have it mixed in.

terrarium substrate layer

In terms of depths, I go for about an inch of leca and an inch of soil, BUT it’ll depend on the size of your terrarium. As long as you have enough to cover the area properly it’s fine.

One thing I will recommend is to dampen the substrate before adding it. Don’t get it dripping wet, but definitely spray it down thoroughly. We need to get that humidity going asap.

Step 5: add decor

In a large terrarium, you’ll need some structural decor to add a bit of height and interest.

I used bogwood because I had it, and also I wanted something that the aerial roots of my plants could attach to.

terrarium decor

I also added lights at this point. You don’t need to add lights, but it’ll really elevate the look of your terrarium. If it’s in a sunny spot, then you don’t need them, but mine is in a dark corner.

Our lights are Fluval Aquasky 2.0s. repurposed from the aquarium. They’re controlled via Bluetooth and an app. I’m pretty sure you could find something cheaper, but I don’t have any recommendations that I’ve personally tried.

This aquarium doesn’t have a lid, so one was fashioned from some firm plastic sheeting that we could attach the lights to.

The lights have a blue, dusk setting that looks extremely cool:

Yes, we have a fogger because 1. we’re extra, and 2. it’s easier than spraying it down manually.

Step 6: add plants

As well as plants we added almond leaves, because they look cool and create a nice habitat for the springtails and isopods we have living in there.

In terms of plants, go for things that will really thrive in humid conditions. I love keeping Calathea in there, because they LOVE it. They don’t look that great atm because the slugs love ’em, but they grow so quickly.

Get a variety of ground cover plants and climbing ones. I currently have a Rhapidophora tetrasperma, some kind of small-leaved begonia, a Marble Queen Pothos, a regular green Pothos, a Calathea velvet touch, a Calathea Beauty Star, and pink Aglaonema.

Dave’s snuck a fern in at the back

It’s extremely tempting to get as many plants in there asap but I prefer to put a few in and wait for them to get established and start growing. I think it’ll end up looking more striking if I have a few big plants rather than a tonne of tiny ones, but ultimately it’s personal preference.

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What supplies do you need to make a terrarium?

Basics:

  • A terrarium
  • Drainage layer
  • Membrane
  • Substrate
  • Plants

Nice to have:

Make sure you buy wood for terrariums, otherwise it’ll rot. I use bogwood. You can get it online, but you’re better off to going to an aquarium supplies shop and finding pieces that you like.

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Is it cheaper to make or buy a terrarium?

It really depends on what you’re going for.

You can buy AWESOME terrarium kits from shops like this one on Etsy but they’re much pricier than the terrariums you usually see in shops. But they’re good. Like, really good. Not foolproof, because nothing in this hobby is, but worth the money if you do a bit of research.

The cheap ones you can buy in shops are often filled with inappropriate plants that will die pretty soon unless you’re gonna give it a TONNE of attention (which for me negates one of the main attractions of terrariums, which is that they pretty much care for themselves).

You tend to get what you pay for, is what I’m saying.

If I just wanted one small terrarium, I’d spend the money on a good kit, like one from the Etsy shop I linked above.

If you’re making a big terrarium, price isn’t the issue (I don’t mean that I’m rich but that it’s not even a consideration here). You can’t really buy them already made up, and the few that pop up are PRICEY.

And they’re not cheap to make. If I bought everything that I used for the one pictured here now, I’d be looking at over a grand’s worth of gear and still only have the tank, stand, and lights.

You could easily halve that by buying a used aquarium, but you’d have to factor in collecting it (hire a man with a van or something – aquariums often sell for 75% cheaper than they were bought for because people exit the hobby so frequently, the only issue is moving the damn things).

Uniquely though, you could MAKE money with a terrarium. I’m not saying you could operate a business from it, but you could buy, say, a rhapidophora tetrasperma and sell cuttings, and recoup your losses. The plants grow quickly and cuttings root quickly, so you could cover your costs in about a year.

That may sound a bit, er, crap BUT there are VERY few hobbies that allow you to make a bit of money for relatively little work. Things like breeding fish or teaching classes can’t really be done as casually/easily as propagating plants.

BUT THEN

If you want a small terrarium and have about a tenner, you could add some gravel and soil to a large mason jar, stick in a fittonia and be done. You could do this on a bigger scale with a plastic box.

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Do you need to put charcoal in a terrarium?

You don’t NEED to put charcoal in a terrarium, but charcoal stops mold from growing.

That being said, you might not need to buy extra charcoal to put in your terrarium, because a lot of terrarium soil mixes already have carbon/charcoal added.

Charcoal isn’t something to cheap out on, so don’t miss it out as a way to save money, because it’ll come back to bite you in the ass. The place to save money on terrariums is the vessel itself, because as long as it lets in plenty of light and is fairly sturdy, you can use whatever you like.

There are alternatives to charcoal – so you can add things like springtails that will eat mold, but charcoal is the easiest and cheapest thing to use. I use aquarium carbon, because I can steal it from my boyfriend it’s pretty affordable and less messy than charcoal.

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Do you need to water terrariums?

Yes, you need to water terrariums, but it’s not the same as watering normal house plants.

It’s actually kind of the opposite: generally with house plants you give them a lot of water occasionally, but with terrariums, you add a little water regularly.

I have a whole article on watering terrariums here, which I recommend you read (but then I would, wouldn’t I?) but here’s the tl;dr:

Most people won’t need to spray their terrarium down every day. We do to ensure humidity stays up for the frog BUT ALSO do NOT underestimate getting into a routine. If spraying your terrarium becomes part of your daily routine you’re less likely to forget.

But also if you go away for a couple of weeks your terrarium is unlikely to dry up to the point that it affects your plants.

You can get a fogger that goes on automatically so you don’t need to spray (this is great if you want plants like ferns that do NOT like getting water on their fronds) or you can put a hygrometer in

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How do you fertilise a terrarium?

We have a bio active terrarium, so we have little bugs (springtails and isopods) that eat decaying matter and then poop out nutrients. This means that we don’t have to fertilise.

If you don’t want to do that, then I would recommend adding fertiliser to your spray bottle every month or so. Because the spray will inevitably hit some of the leaves, you don’t want to use a harsh chemical fertiliser, because you’ll risk damaging the leaves. Instead, use a foliar spray (an orchid spray would work) or a natural fertiliser like seaweed emulsion.

Fish emulsion will smell. You have been warned.

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What happens if you overwater a terrarium?

If you overwater a terrarium it will rot, and pretty quickly. If you use the spray method you shouldn’t overwater though, because the soil never gets particularly wet, it’s just damp.

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How long will a terrarium last?

Terrariums last the same amount of time as a lot of house plants: until you get sick of them.

A well-maintained terrarium can last forever. Sure, plants may die occasionally, or you’ll have to trim them back, but there’s no reason why it shouldn’t last forever.

There’s a sealed terrarium that’s been around since the 60s, and there’s no reason why a closed shouldn’t last a lifetime.

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And that’s it! Drop a comment if you have any questions, or if there’s something I haven’t explained very well. There are probably a myriad of different ways to make a terrarium, so I’m not saying that this is the right or only way – it’s just what I did.

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