In 1829, a 23 year old botanist named Nathaniel Ward had a hobby of studying insects kept in jars. In one, he had placed a moth chrysalis on damp soil and covered it with a lid, only to come back some time later and find a fern and some grass growing in the soil. He continued his experiments with this so-called “Wardian Case” and published his results. A few years later, a man who regularly shipped plants between Australia and Britain named George Loddiges (whose family maintained a very reputable plant nursery as well as having great influence in several horticultural societies) began planting his shipments in Wardian Cases before shipping them. This skyrocketed his success rates, and plant enthusiasts have been in love with what we now call terrariums ever since!
Contrary to the conditions of their discovery, today the world of terrariums has somehow developed a bit of a reputation of being high maintenance! We’re here to tell you that keeping your plants under glass is actually one of the easiest ways to care for and maintain your plants so long as the basic components are set up properly. If it wasn’t easy, good ol’ Nathaniel Ward wouldn’t have accidentally discovered how effective terrariums are at cultivating plants while bug collecting.
The idea behind a terrarium is that the glass captures all of the moisture and nutrients to be reused over and over again by the plant and the soil. It goes like this:
- The plant absorbs water and nutrients from the soil. The nutrients are stored in the plant or used for growing, and the water evaporates off of the leaves once the plant is done using it.
- The water that was evaporated makes the air much more humid and eventually collects on the inside of the glass. It then runs or drips back down into the soil, where it can be reused by the plant countless times.
- The nutrients that the plant uptakes are reintroduced into the soil once old leaves fall off and decompose. The soil also has its own micro-ecosystem going on, where bacteria die and decompose and are used again and again by the other microbiota.
This system could theoretically go on indefinitely - in fact, a man named David Latimer from Cranleigh, Surrey, has had a closed terrarium since 1960 and in all the years since has only added more water to it once!
Terrariums can be made as either open or closed ecosystems, and both styles have their pros and cons. We generally construct open terrariums for beginners. While it’s true that closed terrariums have the potential to maintain themselves indefinitely, open terrariums are usually more suited for decor and are much easier to access if they need anything plus require much less careful setup in the beginning
How to build an open terrarium
Here’s everything you’ll need before starting:
- A piece of glass with an opening
- Pea gravel
- Organic potting soil
- The plants you want to put inside (we recommend choosing tropical foliage plants over succulents, as succulents are easily overwatered in containers that lack a drainage hole and don’t generally appreciate humidity)
- Biochar (activated, PH balanced, nutrient enhanced charcoal)
- Tweezers, chopsticks, or some other apparatus along those lines (we highly recommend chopsticks). You may also find a small spoon helpful.
- Bacterial inoculant
- A small mister
- To begin, add just enough biochar to cover the bottom of your glass. This layer is here as a defense against overwatering. If you accidentally overwater your terrarium and the extra water collects in the bottom, the biochar will keep that water acidic enough that bad things like mold and mildew will have trouble forming. It can also help maintain the size of your plants inside your new ecosystem.
- Next, add your pea gravel. This layer can really be as thick as you want, so long as it’s at least twice the depth of your biochar layer. The gravel’s main purpose is to act as a defense against overwatering - it gives all the runoff somewhere to go that isn’t the soil, where it would otherwise rot. If you want to do any aesthetic landscaping (such as making a hill or a valley) this is the layer to do that in. Pro tip: making the gravel in the back taller than the gravel in the front will angle the plants forward nicely.
- Your soil goes directly on top of the gravel layer. This soil layer doesn’t need to be as thick as you might expect! Make it as even as you can and only about an inch deep. It won’t seem like enough to you when you look at it, but restricting this layer keeps the plants working together for nutrients instead of fighting for domination. And don’t worry about mixing in perlite or anything like that: this layer is thin enough that it’s going to drain pretty well no matter what, and if the roots need more oxygen they can get it from the gaps in the gravel layer. If you’re worried about that, just fluff the soil instead of tamping it down so that it has plenty of air flow.
- Lastly, plant your plants using your chopsticks or other apparatus. Clear the soil from the roots, and grab the plants at their base, just above the root mass. Then push their roots down into the soil layer so that none of their roots are showing. If you’re having trouble getting the plants to stand up straight, it’s okay to push them down into the gravel layer a little bit.
- Be gentle if you can, and try not to mix up the soil and gravel too much - but a little bit of mixup is ok.
- Make sure you plant everything close together! You want their roots to be touching. To that end, it’s a very good idea to have enough plants to completely fill out your terrarium without big gaps between the plants. This will help prevent any of your plants from dominating or monopolizing the space in the terrarium.
- Fill in any empty spaces between plants. For foliage terrariums you can use moss or ground cover. Props, rocks, and pebbles are also great options. Don’t use moss for terrariums with arid plants (mainly cacti and succulents).
- Pro tip: plant the tallest plants first in the back and then work your way towards the opening with the shorter plants. Any future care is going to be a lot easier if you make sure the tallest plants are not between the opening and the shorter plants, plus it results in a more natural looking landscape.
- You can add crystals or small props or whatever you’d like to the terrarium at this stage. This is where you get to really personalize your creation and show off your style!
To care for your terrarium:
- Mist the inside of the glass all around your plants to allow the water to trickle down. You’ll know you’ve watered enough once the soil layer looks darker and “sticky” all around, and stop watering as soon as you see any water building up in the bottom. How often you water depends on the plants you’ve chosen, but it’s easier to just check on it a couple times a week than it is to try to follow a strict watering regimen. Because the needs of your terrarium will fluctuate as the seasons and conditions in your home change, we encourage you to have a “check on it” schedule rather than a watering schedule. Watch for drooping or crisping as indicators of thirst, and we can’t stress enough to avoid water pooling in the bottom.
- If in doubt, we recommend using water that has been filtered, distilled, or otherwise purified, but simply leaving tap water out overnight to let the harmful chemicals evaporate off will make a big difference. Many people just use water from their Brita pitcher, and that works just fine so long as the water is not still cold when you put it in the terrarium. Plants don’t like cold feet!
- To make sure your terrarium has enough food, give it some bacterial inoculant once a month. Steep a pinch of inoculant in the water you’ll mist your terrarium with to make a sort of “tea” and then water as normal. It doesn’t keep once it’s hydrated, so use a new pinch of inoculant each time. Alternatively, you can apply a pinch to the topsoil sprinkled evenly across the surface monthly.
- Most foliage plants that you would place in a terrarium want bright but indirect light, so place your terrarium near but not directly in front of a window that gets sunlight for at least a good chunk of the day. The leaves that the plants grow will reflect how happy they are with their lighting situation: if the leaves are pale and sickly, they would like more sunlight; if the leaves have yellow or crispy spots that are unevenly distributed, they are being sunburned. But don’t fret! Plants grow new leaves to tolerate reasonable differences in lighting - it’s usually only when the lighting situation is dramatically incorrect that they’ll display these signs of stress.
- Like any other living thing, your plants are not going to like being too cold or too hot. The temperatures they can handle are the same temperatures that you would like your house to be, which is between 65 and 85 degrees.
To summarize: mist your terrarium when it starts to look thirsty, feed it once a month, and don’t cook or freeze it! Plants are very good communicators and you’ll almost always know right away what it needs if you check on it once a week.
Once it’s built and placed, your terrarium will be a beautiful, low-maintenance decor piece that’s fascinating to watch develop over the coming months. Plants that outgrow the space a little are usually safe to trim back, and if you keep up with your once a month inoculant you’ll see many plants flower! It’s an amazing feeling to witness something you’ve cared for thrive and bloom.
The nice thing about terrariums is that if one plant dies, it usually is just the one plant that dies and it can then easily be replaced. Ecosystems that have many plants share nutrients and water across their roots (which is why you want your plants to touch roots when you’re planting them), and they’re very good at recognizing what plants in the system need nutrients. If one plant dies, chances are it got cut off from the network for some underlying ailment that the ecosystem quarantined to keep from spreading to the other plants. Isn’t that incredible? If you see a plant die, just remove it and inspect the terrarium to see if anything obvious is going wrong. If everything seems okay, the rest of the plants will swoop in to fill the space and everything will be perfectly fine.
Because we limited the depth of the soil layer, your plants are going to have a hard time outgrowing your terrarium and will stay close to their original size for a very long time, so no need to worry about repotting.
Once you really get into terrarium building, you start to see just how much easier it is than maintaining individually potted plants. Plants look out for each other once they get to know each other. Terrariums, like gardens, forests, and other plant collectives, are incredibly resilient and will generally come back to life no matter what life throws at them, but plants that are by themselves in their pots don’t have friends to back them up. It’s inspiring to see the plants in your new terrarium support each other over the coming months!
If you have any questions about terrarium building or want some help doing it, don’t hesitate to come into the shop and ask for assistance! We love building terrariums and always enjoy teaching others how it’s done. Good luck, and don’t forget to show us your creations by tagging us on Instagram @urbansproutsstore when you’re done!