Open terrariums, or as I like to call them – bowls of plants.
Just kidding. They may not be a terrarium in the truest sense of the word, but there’s still a place in my home for interesting collections of plants, curated in beautiful containers.
Besides, open terrariums come in many forms. Most people (quite rightly) think of succulent and air plant terrariums, but some of the more forgiving terrarium plants can still grow in an open terrarium too.
Generally speaking, open terrariums are much simpler than a functional closed terrarium – making them a versatile choice for the home.
That being said, they do have their own unique requirements. If you plant your succulents like you do your ferns, you’re going to have a problem.
So, in this article you’ll learn when to plant an open terrarium vs a closed terrarium. Which plants to choose, and how ultimately to build and care for your open terrarium.
Why Make an Open Terrarium?
Open terrariums are popular, and for good reason.
They’re a great way for people to get started with terrariums and I’m 100% behind that. You still get all the experience of planting and building a terrarium, but you don’t have to deal with many of the factors that can easily kill a terrarium.
That makes open terrariums a more versatile when it comes to home decor. Hence the rise of hanging air plant terrariums and geometric succulent terrariums.
They’re often more ornamental than horticultural, but they come with plenty of direct advantages:
- Better airflow for plants
- No condensation issues
- Lower risk of mould and rot
- More forgiving, higher chance of success
What you gain in simplicity, you lose in utility.
Open terrariums are not self-sufficient, and many wonderful tropical plants are closed off to them (and personally, I don’t find growing succulents nearly as rewarding).
When to Make an Open vs Closed Terrarium
To open, or not to open – that is the question.
Though in reality, it’s an easy one to answer.
In terms of appropriate plants, open terrariums are the polar opposite to closed terrariums. So, depending on which plants you’re looking to grow, there is generally only one suitable choice.
If your plants like moisture and humidity, you need a closed terrarium. If your plants don’t, you need an open terrarium.
Simple stuff, though there are still versatile plants that can do fine in both.
Open Terrarium Plants
Plants suited to life in open terrariums tend to be mostly succulents, air plants and cacti.
Essentially all the kinds of plants can thrive without humidity and consistent moisture. So naturally, people go straight to the other end of the scale to the plants that thrive in arid environments.
Succulents and cacti have similar care requirements too, so it’s easy to put them together in an interesting mix of textures and shapes.
Though, you’re not limited to arid plants (even if Pinterest suggests otherwise).
We don’t have to cater to the extremes, there’s a lot of grey area between desert and jungle plants.
Remember, an indoor open terrarium has the same environmental conditions as your house. If your houseplants are thriving in a pot on the windowsill, they’ll do just fine in an open terrarium too.
There are lots of houseplants that I’d love to put in closed terrariums (e.g. Philodendron, Maranta, Monstera species) but they’ll grow too big and burst out the top. Not a problem for open terrariums…
In fact, open terrariums can be a great option for the more aggressively growing plants. Vining plants like Syngonium Podophyllum, Pothos, and English Ivy are great choices for mounted open terrariums where they can spill out and hang down the walls.
Open Terrarium Moss?
If you frequent Pinterest, you’ve probably seen many an open terrarium full of tropical mosses. Lush, wavy tufts of moss nestled between succulents?
Looks good, sure. But I can guarantee they didn’t last longer than a week.
The reality is that moss is very difficult to grow in an open terrarium environment.
Looking at the above example, you can see a cactus planted on a bed of lush, green moss. That’s like storing your ice cream on top of your radiator, two very different worlds.
Keeping one happy will kill the other.
Moss (almost universally) likes constant moisture. Without the humidity and moisture trap of a closed terrarium environment, it dries out real fast. Though I guess if you keep your open terrarium near a humidifier and water it super regularly, you might have a fighting chance.
You’re better off using some preserved moss like this reindeer moss. It can still look vibrant (though it often looks a bit dry) and adds that extra fluffy texture, without any care required at all.
Open Terrarium Layers
The composition of your open terrarium will vary depending on which style you’re going for and which plants you choose.
Open houseplant terrariums for example, can be very forgiving. Some may need a drainage layer, but many can be as simple as substrate + plants. After all, they’re essentially just a glass pot right?
Arid terrariums however (e.g. a cactus terrarium), require a very different structure and substrate.
Good drainage is an important part of any terrarium substrate, but with arid plants – drainage is critical.
Succulents and cacti will quickly succumb to rot if the roots are sitting in moist substrate. So, that’s why arid substrate mixes containing lots of sand and rock work well.
You can buy premade cactus and succulent mixes too, but the experts over at Succulents and Sunshine recommend adding a significant amount of perlite or pumice to these mixes (like 50:50) in order to achieve the right level of drainage.
Plus, a false bottom is always recommended. When growing arid plants in pots, you always have a drainage hole at the bottom. We can’t do that with terrariums, so we need to create a reservoir inside instead.
Open Terrarium Care
To be honest, there’s no real science to open terrarium care.
Without the need to finely balance a tiny ecosystem, you’re essentially just trying to keep your plants fed and happy. It’s no different to looking after your houseplants, but often that’s hard enough right?
So, if you’re used to keeping succulents or houseplants in pots around the house, you can usually treat your open terrariums in much the same way.
Seeing as open terrariums have no natural water cycle, it’s going to fall to you to keep it topped up. Sorry!
Watering requirements and methods will vary with your plants.
Succulents have their own watering preferences. Experts advise that they like to have their roots soaked with water, but then being allowed to dry out again for a few days. So unlike closed tropical terrariums, misting isn’t recommended.
Air plants enjoy a good dunking in water every now and again, and houseplants will need as much water as is usually necessary.
Where closed terrarium plants are almost all shade-loving plants, open terrarium plants are often the opposite.
Which means you can actually put these by the window and show them off!
Succulents like to have several hours of direct sunlight a day, so they’re best placed on a windowsill where they’ll get some morning rays. Houseplants will vary.
Being open to the environment, open terrariums are much more susceptible to bugs, pests and infestations.
Sadly, mealy bugs and gnats have been the death of many noble houseplants. So you’ll need to be extra vigilant on that front.
Generally, if you see your plants rapidly declining, there’s a good chance it’s down to an insect of some sort. Give them a good inspection, try to identify the little buggers causing the problem (here’s a good resource) and treat accordingly.
Terrariums containing houseplants and vines tend to quickly outgrow their vessels. Some intentional spill-over can look great but you might also have to trim a lot more aggressively than with closed terrariums.
Arid plants on the other hand, will require almost no pruning… ever.
You don’t need to deal with condensation in open terrariums – so that’s a plus – but unfortunately now you do need to deal with dust.
I find that you can generally just buff the glass with a microfibre class to get it clean and shiny again. Though if it’s particularly dirty, you can wipe with a wet cloth first (using distilled water so as to not leave calcium deposits on the glass).
If you’re using top stones or gravel on top of your soil, I find a small brush is best to gently dust them off.
Open Terrarium FAQ
Generally no. You’ll have a hard keeping it alive, as moss in an open environment dries out very quickly. Most people use preserved moss in open terrariums instead.
Arid plants like succulents, cacti and air plants are all great choices. Though houseplant varieties can often work well too.
Over to You
I’m interested to hear how you feel about open terrariums.
Do you have any of your own, or maybe even prefer them? Maybe you’ve managed to grow some cool plants that other people haven’t?
Let us know in the comments.