Building naturalistic terrariums with miniatures

A clear glass container, a drainage layer, charcoal, a barrier, and a substrate, in that order from the bottom. I use leca or gravel for drainage, a thin layer of horticultural charcoal to keep the water sweet, a mesh or moss barrier, then a peat-free terrarium substrate on top. A closed glass jar from a homeware shop works as well as a purpose-made tank for around a tenth of the price. The miniatures go in last, once the planting settles.

Humidity-loving, slow-growing ones. Fittonia, baby tears (Soleirolia), small ferns, and most mosses thrive in the still, damp air of a closed terrarium and stay small enough not to swamp the scene. I avoid succulents entirely, because they rot in that humidity, which is the single most common terrarium failure. Match the plant to a closed, humid environment and it will largely look after itself.

Use waterproof materials and seal everything else. Resin, ceramic, stone, and sealed polymer clay survive indefinitely in a humid terrarium, while raw wood, paper, and fabric will mould or warp within weeks. I seal any porous miniature with several coats of a water-based varnish before it goes in. Even then, I keep the most delicate pieces in open terrariums rather than fully sealed ones, where the humidity is gentler.

A closed one needs almost none, which is part of the appeal. A properly balanced sealed terrarium recycles its own moisture and can go weeks or months without watering, needing only the occasional trim and the removal of any yellowing leaves. Open terrariums need watering more often. The skill is in getting the initial water balance right: condensation should appear and clear daily, not fog the glass permanently.

Easily. A terrarium lives on a windowsill or shelf and needs bright indirect light rather than direct sun, which would cook the plants inside the glass. This is one of the most flat-friendly things on this list, since the whole living scene fits in a jar. I keep mine away from radiators and south-facing glass to stop the temperature swinging.

Too much water, too little air movement at setup, or organic matter rotting inside. White fuzzy mould usually means the substrate is waterlogged or a leaf has died and decayed, so I remove anything rotting promptly and ease off the watering. A cloudy, permanently fogged glass means there is too much moisture, which I fix by opening the lid for a day to let some escape. Springtails (tiny cleanup insects sold for terrariums) eat mould and keep a closed system balanced, which is the trick most beginners do not know.

⚠️ Horticultural charcoal dust and some substrates can irritate the lungs, and a few common terrarium plants are toxic if eaten. Work in a ventilated space, wash your hands after planting, and keep terrariums and their plants out of reach of children and pets. Check that any plant is non-toxic if there is any chance of it being nibbled.