How to Keep a Moss Terrarium Alive: 9 Tips from Plant Experts

People have been spending a lot of time at home, working, watching all the streaming services and picking up a new hobby or two. One of the most popular pastimes has been putting in some plant time, whether it be starting a garden or adding a flower bed around the house. But the hottest trend growing is found encased in glass.

Yes, we are talking about terrariums. The self-contained, artful arrangements have become a plant lover’s paradise. They have a reputation for being low maintenance and add just the right earthy touch to any room’s decor. As a bonus, you can take yours with you if you move. (Try that with a vegetable garden!)

Though terrariums are relatively easygoing, they are still filled with living, growing plants and need some care to live their best lives. Here are a few tips from terrarium experts.

First, you need to know there are two types of terrariums: sealed and unsealed. Each has its own special needs. Traditional terrariums are completely sealed, says Dan Jones, founder of Terrarium Tribe and self-described “plant junkie and would-be terrarium wizard.” Modern terrariums have an opening where air can get in, so what might work well in a traditional setup could cause you trouble with the more trendy variety. 

1. Pick the proper plants

This is where the type of terrarium you have or plan to create becomes important. Jones is firm in his belief that arid varieties aren’t a good fit for classic, closed terrariums. “Sadly, cacti and succulents will quickly rot in high-humidity environments. Stick to tropical plants and you can’t go too wrong.”

However, the newer terrariums without lids embrace the succulents. “We only use succulents or cactus,” says Rachel Song of Modern Terrarium Bar in Rockville Centre, N.Y. “Our customers do not like to constantly water their plants.”

2. Feed the right diet

If your terrarium includes succulents, pay attention to what you feed it. “If you want to use a fertilizer, use the right one,” says Song. “There is specific plant food for succulents. Don’t use regular plant food.”

3. Don’t go overboard on water

Proper hydration is a big deal in the world of terrariums. That isn’t to say they are complicated. Their care just takes a little know-how. A closed terrarium requires less watering than does an open one.

“It is very easy to overwater a terrarium, and unfortunately it can be difficult to rectify once it’s gone wrong,” says Jones. He suggests using a spray bottle and giving the plants just a few spritzes when needed.

The size of your terrarium is a factor as well. “For something small, about 5 inches in diameter and 4 inches tall, you only need two or three tablespoons around the roots of the plants,” says Song. “Remember there is no draining, so if you water too much you are soaking the roots and the plant doesn’t like it.”

4. Figure out water time

“Being a closed ecosystem, terrariums don’t really operate on a regular watering schedule,” says Jones, who is based in England. “All of the water that’s added is trapped in a self-contained water cycle, and it’s our job to interpret and facilitate that cycle.”

Traditional terrariums will lose a little moisture to evaporation, Jones says. “It depends on how tight the seal is or how often you open it up.” In general, sealed terrariums need to have their water topped off about once a month. 

The more open types need a drink a little more often—about once or twice a week, says Song.

5. Keep an eye on the glass

If you are new to terrarium life, knowing exactly when your plants are crying out for help can be tough. Jones has a good tip to follow for that. “The best indicator of good moisture levels is the amount of condensation on the glass,” he says. “A healthy terrarium should show some light condensation on the glass through the day. So if your terrarium is looking clear and bone dry, then it probably needs more water. If it’s looking consistently soaking wet inside, then it likely needs airing out a little.”

Still not sure? Hold off a little while. “It can be challenging to judge at first,” he says, “but it’s better to underwater than overwater."

6. Let the sun shine in

The amount and type of light that you give your plants play big roles in how much they will thrive. Both types of terrariums have similar requirements. “Ideally, we recommend 6 hours of bright, indirect sunlight,” say Song. “The lighting is more important than the watering. If you forget watering, they are very forgiving but if you do not provide enough light, they will not do well.”

Jones concurs with the need for bright and indirect light. “It’s not always the easiest to interpret that in the home,” he says. “If you’re in the Northern Hemisphere, a north-facing window sill will provide this all day long. For rooms with strong light, you can just place your terrarium a few feet away from the direct light source.”

If you don’t have a place in your home that fits this description, you can always use grow lights, though natural light is always best.

7. Don't let it get too cold

Some terrariums do live outdoors, and for those, you will want to be aware of the temperature. Song says any temperature over 54 degrees is good and anything less is too cold. 

“There are some more hardy succulents that don’t mind winter, but in general, they just don’t like the cold. They prefer warmer weather,” she said.

8. More moss, please

Jones has nothing but praise for moss and its importance in the grand scheme of things. “For me, moss is the glue that binds a tropical terrarium together —both visually and sometimes literally—and I believe it should be used freely and liberally.”

9. It's a bug’s life

Finding bugs flying around your plants can be worrisome, and pests taking up residence inside your glassy garden might cause some alarm. Paying attention to what you use to create your terrarium is the trick.

“As long as you’re using high-quality materials that have been stored appropriately, pests don’t tend to be much of a concern,” says Jones. “They are most likely to come in with your substrate, so getting something that’s sealed and fresh is key.”

In fact, adding certain bugs can be very beneficial to your terrarium. “Springtails are tiny and love to feed on mold, so they do a great job at keeping a terrarium fresh and healthy.”

With a little care—and careful planning—your terrarium will thrive, all in its own little world.