What makes a plant suitable for a terrarium
A terrarium plant must tolerate high humidity, low light, and confined space — conditions that would kill most houseplants. The best choices are small, slow-growing plants that thrive in the moist air trapped inside glass. Ferns, moss, succulents adapted to rainforests, and small-leafed vines all work well because they evolved in environments similar to what a sealed or semi-sealed glass container creates.
Size matters more than you might think. A plant that grows six inches tall in open air may reach the glass lid in a terrarium within months. Creeping fig, baby tears, and dwarf varieties of ferns stay compact. Larger plants like pothos or philodendron will eventually outgrow even a big terrarium and need pruning or removal.
The type of terrarium you have — open, semi-closed, or fully sealed — determines which plants will survive. An open terrarium with no lid dries out faster and suits plants that prefer less humidity, like certain succulents. A closed terrarium holds moisture and works for tropical plants that need constant dampness. Knowing which you own before choosing a plant prevents buying something that will rot or wilt inside it.
Key Takeaways
- Terrarium plants must tolerate high humidity and low to medium light, so ferns, moss, and tropical vines are better choices than sun-loving succulents or large houseplants.
- An open terrarium dries faster and suits plants that prefer drier air, while a closed or semi-closed terrarium holds moisture for plants that need constant humidity.
- Check the mature size of any plant before adding it to a terrarium, because slow-growing species can still outgrow the container within a year or two.
- Overwatering is the most common reason terrarium plants fail, so water sparingly and only when the soil is visibly dry at the surface.
- Condensation on the glass walls is normal in a closed terrarium and means humidity is stable; wipe it away only if it blocks your view.
Open versus closed terrariums and what each needs
An open terrarium has no lid or has a lid you remove regularly. It loses moisture to the air, so the soil dries out faster than in a closed container. Plants in open terrariums need less frequent watering — usually once every one to two weeks, depending on your home's humidity and temperature. Fittonia, peperomia, and certain ferns do well in open setups because they like moisture but not constant wetness.
A closed or semi-closed terrarium traps moisture inside the glass. Water that evaporates from the soil condenses on the walls and drips back down, creating a cycle that keeps the soil damp for weeks. These terrariums need water far less often — sometimes only once a month or even less. Moss, baby tears, and tropical ferns thrive in this environment. The trade-off is that closed terrariums can become too wet if you overwater, leading to mold or root rot.
If your terrarium came with a lid but you are unsure whether to use it, start with it off for the first week and observe the soil. If it dries out completely within a few days, your plants likely prefer a closed setup. If it stays damp, an open terrarium may work better. You can always switch later by adding or removing the lid.
Soil, drainage, and the layers that matter
Terrarium soil is not the same as potting soil for regular houseplants. Standard potting soil holds too much water and causes root rot in the humid terrarium environment. Instead, use a terrarium soil mix or create your own by combining equal parts potting soil, perlite, and orchid bark. The perlite and bark create air pockets that prevent the soil from becoming waterlogged.
Most terrariums need a drainage layer at the bottom, even though there is no drainage hole. Place a half-inch to one-inch layer of small pebbles or aquarium gravel at the very bottom of the container. Above that, add a thin layer of activated charcoal — this absorbs odors and helps prevent mold if the soil does get too wet. Then add your terrarium soil mix on top. This layering system keeps roots from sitting in standing water while still maintaining the moisture the plants need.
The total soil depth depends on your container size and the plants you are growing. Small ferns and moss need only two to three inches of soil. Larger plants like creeping fig may need four to five inches. Leave at least one inch of space between the top of the soil and the rim of the container so water does not spill over when you water.
Watering a terrarium without drowning it
Overwatering is the single most common reason terrarium plants fail. Because water cannot drain away, it pools around the roots and causes them to rot. The key is to water far less than you think you need to. For a closed terrarium, check the soil once a month by pressing your finger into it. Water only if the top half-inch feels completely dry. For an open terrarium, check every one to two weeks and water when the surface feels dry to the touch.
When you do water, use a spray bottle or a small watering can with a narrow spout. Add just enough water so the soil becomes moist but not soggy — you should not see water pooling on the surface or running down the sides. A few light mists from a spray bottle are often enough for a small closed terrarium. If you accidentally overwater, tilt the container to one side and use a paper towel to absorb the excess water from the bottom.
Condensation on the glass walls of a closed terrarium is normal and means the humidity cycle is working. You do not need to wipe it away unless it is so heavy that you cannot see the plants inside. If condensation appears constantly and the soil feels soggy, your terrarium is too wet — remove the lid for a few hours to let some moisture escape, then replace it.
Light requirements for terrarium plants
Most terrarium plants come from forest floors where they receive dappled or indirect light filtered through tree canopies. They do not need bright direct sun and often prefer shade. Place your terrarium near a window that gets indirect light — an east or north-facing window is ideal. If your only option is a south or west-facing window with strong afternoon sun, move the terrarium back from the glass or use a sheer curtain to filter the light.
If your home does not have a naturally bright spot, a small LED grow light placed six to twelve inches above the terrarium works well. Terrarium plants do not need intense light like succulents do. A standard LED bulb rated for plants, run for twelve to fourteen hours a day, is enough to keep ferns and moss healthy. Some people use a straightforward timer so the light turns on and off automatically.
Watch your plants for signs that light is too low: pale leaves, slow growth, or leaves that look smaller than they should. If you see these signs, move the terrarium closer to a window or add a grow light. Conversely, if leaves turn brown or bleached, the light is too strong — move the terrarium back or increase the shade.
Temperature and humidity in a terrarium environment
Most terrarium plants prefer temperatures between 65 and 75 degrees Fahrenheit. They tolerate the temperature swings in a typical home, but avoid placing a terrarium directly above a heating vent, air conditioner, or radiator. Sudden temperature changes stress the plants and can cause leaves to drop or growth to slow.
Humidity inside a closed terrarium stays high naturally — often between 80 and 90 percent. This is why closed terrariums work so well for tropical plants. An open terrarium has lower humidity, closer to the ambient humidity of your home, which varies by season and climate. If your home is very dry (below 40 percent humidity), an open terrarium may not hold enough moisture for ferns or moss, and you may need to mist the plants by hand every few days or switch to a closed setup.
If you live in a very humid climate or your home is naturally damp, a closed terrarium can become too wet. In that case, leave the lid off or crack it open slightly to allow some air circulation and moisture to escape. The goal is to find a balance where the soil stays moist but not waterlogged and the plants look healthy.
Pruning and maintaining terrarium plants over time
Terrarium plants grow slowly because of the confined space and lower light, but they do grow. Every few months, check for leaves that are touching the glass or vines that are creeping toward the lid. Pinch off the growing tips of vines to encourage bushier growth instead of long, leggy stems. Remove any dead or yellowing leaves as soon as you notice them — they can trap moisture and encourage mold.
If a plant outgrows the terrarium despite your pruning, you have two choices: remove it and replace it with a smaller species, or take it out and grow it as a regular houseplant elsewhere. Some people rotate plants in and out of terrariums seasonally or as they grow. This keeps the terrarium looking balanced and gives plants a chance to grow larger in a bigger container if you want them to.
Mold or algae sometimes appears on the soil surface or glass, especially in closed terrariums that are too wet. If you see a white or green film, reduce watering, increase air circulation by opening the lid for a few hours, and remove any affected soil from the surface. A small amount of mold is not harmful to the plants, but heavy mold growth means the environment is too damp and needs adjustment.
Common terrarium plant choices and their needs
Ferns are among the most popular terrarium plants because they love humidity and tolerate low light. Maidenhair ferns, button ferns, and rabbit's foot ferns all stay relatively small and do well in closed or semi-closed terrariums. They need consistently moist soil but not waterlogged conditions.
Moss thrives in terrariums and requires almost no maintenance. It does not need soil — just a thin layer of moist substrate like bark or peat moss. Moss grows slowly and adds texture and green color to a terrarium. It tolerates very low light and high humidity.
Peperomia and fittonia are small-leafed tropical plants that prefer warm, humid conditions. Both stay compact and have attractive foliage. They need bright indirect light and consistently moist (but not soggy) soil. Both do well in closed terrariums.
Creeping fig and other small-leafed vines add height and visual interest to larger terrariums. They grow slowly in the terrarium environment and can be pruned to shape. They prefer bright indirect light and humid conditions.
Succulents can go in terrariums, but only in open setups with infrequent watering. Echeveria, jade plants, and other drought-tolerant succulents rot quickly in the moist environment of a closed terrarium. If you want succulents, use an open terrarium, water very sparingly, and choose a location with bright light.
Frequently Asked Questions
Can I use regular potting soil in a terrarium?
Regular potting soil holds too much moisture and causes root rot in terrariums. Use a terrarium soil mix or make your own by combining potting soil, perlite, and orchid bark in equal parts. The added perlite and bark create air pockets that prevent waterlogging.
How often should I water a closed terrarium?
Check the soil once a month by pressing your finger into it. Water only if the top half-inch feels completely dry. Many closed terrariums need water only once a month or even less, because the sealed environment recycles moisture. Overwatering is far more common than underwatering.
What does condensation on the glass mean?
Condensation is normal in a closed terrarium and shows that the humidity cycle is working. Water evaporates from the soil, condenses on the glass, and drips back down. You do not need to wipe it away unless it is so heavy you cannot see the plants. Heavy, constant condensation with soggy soil means the terrarium is too wet.
Can I put a terrarium in a dark corner?
Most terrarium plants prefer indirect light and tolerate shade better than sun-loving plants, but they still need some light. A very dark corner will cause slow growth and pale leaves. Place the terrarium near a window with indirect light, or use a small LED grow light on a timer for twelve to fourteen hours a day.
What should I do if my terrarium plant is rotting?
Root rot happens when soil stays too wet. Remove the plant, cut away any soft or blackened roots with clean scissors, and repot it in fresh terrarium soil mix. Reduce watering frequency and increase air circulation by opening the lid more often. If the plant is severely rotted, remove it and replace it with a new one.