How to Water A Terrarium

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There are loads of different ways to water a terrarium (ok, loads might be a stretch, but there’s probs like, 3), but I favour the spray down method, which consists of misting the terrarium twice a day.

That sounds like a lot, but if you keep a spray bottle by the terrarium and attach the task to another one (for example, after you feed your dog/have your dinner/whatever) it’s the work of seconds.

My terrarium looks like this:

It definitely looks better with the lights on (they’re on a timer and I don’t want to mess with them – Ill try to take a photo tonight but no promises that I’ll remember) but you can how happy the plants are.

Look at the aerial roots on those heartleaf philodendron!

How often should you water a terrarium?

This will depend a lot on the type of terrarium you have.

If you go for a totally sealed terrarium, you pretty much never have to water them.

In all honesty, you may need to unseal it a couple of times to make changes (or release any slugs that have inevitably gotten in there) but because sealed terrariums recycle all their water, you shouldn’t need to add any water.

The terrarium mentioned in the article I linked above hasn’t been watered since it was last opened in 1972. My kind of terrarium.

What’s the best way to water your terrarium?

That all depends on the type of terrarium you have.

We mist ours every day to keep up humidity levels for our frog. However, misting can cause the same issues as it does with misting plants outside of the terrarium.

Some plants, such as maidenhair ferns do NOT like to be misted.

If you want to maintain humidity levels but don’t want some of your plants to brown off, you can buy foggers that will mist your terrarium with a much finer spray (it looks like clouds – pretty cool) than a spray bottle.

The problem with these is that they’re almost too efficient. We had one, but it was too strong and our terrarium was bathed in cloud – and we don’t want to freak out the frog. If you have a very big terrarium, it’s a great option though. You can set them to a timer to make the whole run automatically.

For those of you that have open terrariums with succulents in (not advisable but you do you), neither of these options will be any good.

You’ll need a VERY well-draining soil mix, drainage at the bottom (I’d go for a layer of leca) and a watering can that completely fits into the terrarium so you can water the substrate without wetting the plants.

Water the substrate very slowly and stop as soon as you see the water dripping into the leca – you don’t want a puddle at the bottom.

If you’re intent on having a succulent terrarium, it’ll need to be open, and I’d advise having it under a grow light. I have this one from Mars Hydro, and it’s ideal because as well as providing light, it provides a little bit of warmth too – perfect for evaporating excess water.

Should you mist terrariums?

I’m pretty anti-misting when it comes to house plants, and yet I mist my terrarium.

The difference is that a terrarium is MUCH smaller than a whole room. You can increase the humidity of a terrarium by misting it very effectively.

HOWEVER, not all terrariums need misting. Place a hygrometer in the terrarium and if it reaches your desired humidity without additional misting, great. No need to mist.

Terrariums are essentially closed units, so the water from the substrate will evaporate and condense inside the box without leaving – so you shouldn’t need to add water.

Except realistically, we do need to open and close it for various reasons – cutting it back, rearranging, removing slugs (I assume the eggs get in on the plant leaves – attract them with a piece of cucumber and stick them back in the garden), whatever.

I find that misting is the easiest way to water terrariums, but it’s not without its drawbacks. Some plants will brown off if misted too frequently.

My calathea, pothos, and rhapidophora tetrasperma are fine being misted, but my maidenhair fern fronds brown off.

It doesn’t kill the plant – there’s always plenty of new fiddleheads, but the older fronds go brown and look quite grim. You could easily go in and remove them, but I don’t need the hassle.

For frog-related reasons we add de-chlorinator to the water that we use to mist with.

I definitely need to upgrade to an amber spray bottle and get a label maker for them all.

It’s probably not necessary for plants, but depending on the quality of your tap water, it might be something you want to try – it certainly won’t hurt.

How often should you mist your terrarium?

Somewhere between twice a day and never.

It depends on the kind of plants you have in there.

I use the terrarium as a way to grow plants that like to have higher humidity*. The frog needs humidity of 90% plus, so we mist twice a day.

If you just have plants in there, 70% humidity should be fine – unless you have something like a Monstera obliqua (not to be confused with adansonii).

How often your terrarium will need be misted to maintain humidity will vary depending on the substrate you use, the size of your terrarium, the lighting you have etc etc.

Invest in a hygrometer (they’re usually about £10/15) and see how long it takes for the humidity to reduce below 70% and mist it then. So if the humidity reduces every week, mist it every week.

*Though it’s worth putting in plants like Pothos, that typically aren’t fussy, just to see the crazy aerial roots.

pothos with fuzzy aerial roots climbing up the back of a terrarium
Grim, ya?

What type of water should you use in a terrarium?

It really depends on what you’re growing in there.

If you’re growing plants such as pothos, which don’t really seem to care about water quality, tap water is fine. Add a bit of de-chlorinator, you know, for a treat.

seachem prime dechlorinator
Why for aquarium products? Why?

For those of you using terrariums to grow fancy, expensive plants, it’s probably worth going for filtered water, especially since the majority of the water is going to be recycled anyway.

You could also use filtered water in the spray bottle since so little is used.

If your tap water is good enough for your house plants, it’ll probs be fine for your terrarium.

Terrariums are one of the few times I wouldn’t use rainwater on plants, only because it’s a great way to add bugs to your terrarium.

We already get caddis fly larvae, slugs, and various other nematode-type critters turning up – we don’t need more.

How much water should you put in a closed terrarium?

When you’re just starting out, start by watering your substrate before you put it in.

Dampen it, and squeeze out excess water – not aggressively, just enough that it’s not sopping wet.

Scape your terrarium, and add a humidifier. Spray it down if it drops below 60%. If it keeps dropping significantly, water your substrate but sloooowly. You can always add more water, but removing it from a terrarium is a pain in the bum. Just add a bit at a time.

How do you tell if your terrarium is overwatered?

Everything will rot, and it’ll smell rotten.

Terrariums smell AMAZING. Ours smells like a forest BUT it is bioactive. We introduced springtails and isopods that eat all the decaying matter and fungus.

If your terrarium starts to smell musty or damp, it may be overwatered.

Unfortunately, but the time this happens, there’s not really a lot you can do about it. Terrariums move at a much faster rate than normal house plants- they grow a lot faster, but they rot a lot faster too.

You’ll have to take everything out, dry out the soil, and start again.

As a general rule of thumb, the substrate never needs to be wet – it should just be slightly damp.

Due to the high humidity, the soil shouldn’t ever dry out completely – I literally never water the actual soil – I just spray down the terrarium. Overwatering *shouldn’t* be an issue.

If you’ve decided to go for an open terrarium, you’ve basically got a big plant pot without drainage. The only way to not overwater is to be veeeery careful about adding water in the first place.

Am I trying to convince you not to have an open terrarium? Yeah, kind of. I get that they look cool, but they don’t have the benefits of a closed terrarium (high humidity, low maintenance) and it can be struggle to get plants to thrive.

How do you keep moisture in an open terrarium?

An open terrarium is no different to having a normal house plant.

Ergo, the only way to keep moisture in an open terrarium is to get a humidifier or put it in a humid room.

The only things you could do to help are pretty hit and miss, such as:

  • Covering it at night
  • Putting in a little bowl of water, especially if you…
  • …Put a heat mat underneath

Aaaand that’s all I have to say about that. If you have any questions about watering terrariums, please leave me a comment below!

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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