DIY Mini Terrarium: Build a Tiny Glass Garden in an Afternoon
There is something a little magical about a tiny garden sealed inside a glass jar. You look in and there is a whole miniature world: soft green moss, a pink-veined fittonia, a baby fern unfurling against the glass. A mini terrarium is one of my favorite projects because it takes about an hour, costs very little, and gives you a living piece of green you can set on a desk, a bookshelf, or a kitchen windowsill.
It is also a great project for Arizona, where the air is so dry that a lot of humidity-loving houseplants struggle. Inside a closed jar, those same plants are perfectly happy, because the glass traps moisture and creates its own little rain cycle. Here is exactly how I build a mini terrarium, step by step, from choosing the container to keeping it healthy for years.
Closed vs. Open Terrariums: Pick Your Style First
Before you gather anything, decide which kind of terrarium you want, because it changes the plants you choose.
Closed terrariums have a lid, cork, or stopper. Moisture evaporates from the soil, condenses on the glass, and drips back down. They are ideal for tropical, humidity-loving plants like ferns, fittonia, moss, and baby tears. Once balanced, they need water only every few weeks, sometimes months.
Open terrariums have no lid. They work well for plants that like drier air and good airflow, like small succulents, cacti, and air plants. Succulents in a closed jar almost always rot, so do not mix the two styles.
This guide focuses on a closed mini terrarium with moss and tropical plants, since that is the classic version and the one most people picture. I will add notes for a succulent version near the end.
What You Need
The supply list is short, and you may already have half of it around the house.
A clear glass container with a lid: A mason jar, a cookie jar, an apothecary jar, a large pickle jar, or a thrifted glass canister. Anything from about one quart up works well.
Drainage layer: Small pebbles, aquarium gravel, or LECA clay balls.
Activated charcoal: Horticultural or aquarium charcoal helps keep the terrarium smelling fresh.
Barrier layer (optional): A piece of mesh, landscape fabric, or a thin layer of sphagnum moss to keep soil from sifting into the rocks.
Potting mix: A light, airy indoor mix. You can blend regular potting soil with some coco coir and a little orchid bark.
Live moss: Sheet moss or cushion moss from a garden center or terrarium supplier.
Small plants: Two or three slow-growing tropicals in 2-inch pots.
Tools: A long spoon, chopsticks or a wooden skewer, scissors, a small spray bottle, and a paper funnel or rolled-up piece of paper.
Decor (optional): A small stone, a piece of driftwood, or a tiny figurine.
If you want everything in one box, a terrarium starter kit with charcoal, pebbles, and tools is an easy shortcut: https://www.amazon.com/s?k=terrarium+starter+kit+activated+charcoal&tag=greenthumbh0a-20
Choosing Plants That Stay Small
The secret to a terrarium that looks good for years is choosing plants that grow slowly and stay small. Here are my favorites for a closed jar:
Fittonia (nerve plant): Pink, white, or red-veined leaves. It loves humidity and is almost made for terrariums.
Mini ferns: Button fern, lemon button fern, or small maidenhair ferns.
Baby tears: A soft, creeping groundcover that fills in around the moss.
Polka dot plant: Speckled pink or white leaves. It grows quickly, so pinch it back.
Small peperomia: Many compact varieties do well in humid jars.
Moss: Cushion moss or sheet moss for the carpet.
For a one-quart jar, two plants plus moss is plenty. For something bigger, three or four. It is tempting to cram in more, but plants need a little space to grow.
Step-by-Step: Building Your Mini Terrarium
Set up on a table covered with newspaper or an old towel. Terrarium building is a little messy, and that is part of the fun.
Step 1: Clean the Glass
Wash the jar with warm soapy water, rinse well, and dry completely. Any leftover residue can encourage mold or bacteria later. Wipe the inside with a little white vinegar for a streak-free finish.
Step 2: Add the Drainage Layer
Pour in about 1 inch of pebbles or LECA. In a tall jar, you can go up to 2 inches. This layer gives excess water somewhere to collect so the roots do not sit in soggy soil. Use a paper funnel to keep dust off the sides of the glass.
Step 3: Add Activated Charcoal
Sprinkle a thin layer of activated charcoal, about a quarter to half an inch, over the pebbles. It helps absorb odors and impurities in a closed system.
Step 4: Add a Barrier Layer
If you are using mesh or a thin layer of sphagnum moss, lay it over the charcoal now. This keeps soil from washing down into the drainage layer over time. It is optional, but it keeps those layers looking crisp through the glass.
Step 5: Add the Soil
Spoon in 2 to 3 inches of slightly damp potting mix. Damp soil is easier to shape and less dusty. Build it up a little higher in the back so the finished terrarium has depth. Press it lightly so it is firm but not packed.
Step 6: Plant Your Plants
Gently remove each plant from its pot and tease away some of the old soil. If the root ball is large, trim it back a little with scissors. Use a spoon or your fingers to dig a small hole, set the plant in, and firm the soil around it with a chopstick. Place the tallest plant in the back or off to one side, and keep leaves from pressing flat against the glass.
Step 7: Lay the Moss
Tear the moss into pieces and press it onto the soil around the plants, tucking the edges in with a chopstick. Leave a little soil visible if you like the look, or cover everything for a lush carpet.
Step 8: Add Decor and Clean Up
Tuck in a stone, a bit of driftwood, or a little figurine. Then use a paper towel wrapped around a skewer to wipe soil smudges off the inside of the glass.
Step 9: Water Lightly and Close the Lid
Mist the plants and moss a few times with a spray bottle. You want the soil damp, not wet, and you should not see water pooling in the pebbles. Close the lid and you are done.
The First Two Weeks: Finding the Balance
A new closed terrarium needs a little time to settle in. Watch it closely for the first couple of weeks.
A little fog in the morning is normal. Light condensation that clears during the day means the water cycle is working.
Heavy fog that never clears means too much water. Open the lid for a few hours, or a whole day, to let some moisture escape. Repeat until the glass is mostly clear by afternoon.
No condensation at all means it is too dry. Give it a few more spritzes and close it back up.
Once you find the balance, a closed terrarium can go weeks or even months without water. I check mine about once every two weeks and mist only when the moss starts to look a little pale.
Where to Put Your Terrarium
Light is where most terrariums go wrong, especially in Arizona.
Bright, indirect light is best. A spot a few feet back from a north or east window is ideal.
Never put a closed terrarium in direct sun. Glass magnifies heat, and an Arizona afternoon can cook the plants in a single day.
Grow lights work great. A small LED grow light on a timer for 10 to 12 hours a day keeps plants compact and green.
Keep it away from heat and AC vents. Steady room temperatures between about 65 and 80 degrees are perfect.
If the plants start stretching toward the window or losing color, they need more light. If the leaves look scorched or the jar feels hot, move it out of the sun right away.
Ongoing Care and Troubleshooting
Terrariums are low-maintenance, but not no-maintenance. Here is what to watch for:
Mold: A little white fuzz on soil or decor is common early on. Remove it with a cotton swab and air out the jar. Persistent mold usually means too much water and too little airflow.
Yellow or mushy leaves: Usually overwatering. Open the lid and let it dry out a bit.
Crispy brown moss: Too dry or too much light. Mist and move it to a shadier spot.
Leggy plants: Pinch or trim them back with long scissors. Trimming keeps plants small and bushy.
Plants outgrowing the jar: Swap them out for a fresh, smaller plant and replant the big one in a pot.
Some people add springtails, tiny harmless bugs that eat mold and decaying leaves. They are optional, but they work like a little cleanup crew.
Making an Open Succulent Version
If you love the look of succulents, you can use the same basic layers in an open container. The changes:
Use a wide-mouthed bowl or vase with no lid.
Use a gritty cactus mix instead of regular potting soil.
Choose small succulents like haworthia, baby echeveria, or small jade, and skip the moss.
Top-dress with sand, small pebbles, or decorative gravel.
Water sparingly, only when the soil is completely dry, using a squeeze bottle aimed at the base of each plant.
Give it bright light, including a little gentle morning sun.
Succulent terrariums need more light and much less water than closed ones. If you love tiny succulent gardens, our fairy garden planter project is another fun way to play: https://www.greenthumbhobbies.com/post/fairy-garden-planter
Fun Ideas and Variations
Once you have built one, it is hard to stop. A few ideas:
Gift jars: Small mason jar terrariums make thoughtful, inexpensive gifts. Add a ribbon and a care card.
Kid-friendly builds: Kids love picking their own plants and figurines. Use plastic containers for young builders.
Themed terrariums: Build a forest scene, a tiny campsite, or a beach with sand and a shell.
Kokedama pairing: If you like working with moss, try our kokedama moss ball project too: https://www.greenthumbhobbies.com/post/kokedama
A Tiny Garden for Any Season
A mini terrarium is one of those projects that pays you back every day. It brings a bit of green into a room, it keeps humidity-loving plants happy even in a dry desert house, and it is just plain fun to look at. Grab a jar, a few small plants, and a handful of moss this weekend, and in an afternoon you will have your own little glass garden.
Comments