Ever wished you could grow a self-sustaining garden right on your windowsill? A terrarium makes that possible. These are tiny, living worlds sealed in glass—miniature gardens that practically take care of themselves.
What makes them so magical is their built-in water cycle. When sunlight warms the container, the plants inside heat up too. To cool themselves down, they release moisture and a bit of heat through their leaves into the air. This is called transpiration, and it not only cools the plant but also helps pull water and nutrients up from the roots. In a closed terrarium, that moisture rises, condenses on the cooler glass walls, and eventually drips back into the soil just like rainfall. This cycle keeps the environment humid and balanced, which is why closed terrariums rarely need to be watered at all.
Do you want to build a terrarium that you don’t need to take care of? I do too! It’s easier than you think.
1. Start with a clean glass container — we’re using a 16 oz container for this guide. If your hands don’t fit inside the jar, you can use tweezers, tongs, or wooden skewers to help place and adjust the materials as you build.
2. First, add a layer of small rocks or gravel: 2 parts, or ¼ cup for a 16 oz container. This helps with drainage and prevents plant roots from rotting.
3. Next, add 1 part of activated charcoal — about ⅛ cup in our case — on top of the gravel to prevent fungi from growing on the stones when they are wet.
4. Spread a thin layer of sheet moss over the stones and charcoal to keep your next layer of potting soil from mixing in with the charcoal and stones.
5. Then, cover the gravel and charcoal with 4 parts of sterile potting mix — about ½ cup for a 16 oz container. Altogether, these base layers should fill about one-quarter to one-third of the container to leave room for the plants to grow.
6. Now you’re ready to plant. Choose small, slow-growing plants that like humidity and gently tuck them into the soil, making sure there’s about half an inch of soil above the roots.
7. Once you’ve finished planting, wipe the inside of the glass and close the lid for a clean, clear finish.
If you’re making an open terrarium, succulents and cacti are better suited, since they prefer drier conditions.
Put your terrarium where it will get bright, indirect light, and avoid direct sunlight, which can overheat the container. The biggest mistake people make is overwatering the terrariums. For open terrariums, add water with a spray bottle or tablespoon once a week or when the soil is dry. Stop when you see the water begin to collect at the bottom of the terrarium. For closed terrariums, you may only need to water every 4-6 months.
Keep an eye out for condensation on the plants and dry soil. Condensation should form on the inside of the container and eventually run back down into the soil to serve as a water supply. If it forms on the plants instead, then the interior is too moist. Keep the cover off for a time each day until the plants are dry; this can take 15 minutes to an hour. If the soil dries out, add water in small portions and stop if you see it begin to sit and not absorb into the soil.
Once it’s set up, all you need to do is occasionally trim the plants or remove damaged leaves and enjoy watching your mini ecosystem thrive!
