You can put together a decent closed terrarium for 25 to 30 € if you supply the container and the tools yourself. The three areas where you genuinely save money are the glass, the tools and the plants; the two where you should not cut corners are the substrate and the drainage, because a mistake there is paid for within a few months by a waterlogged terrarium.

Where the savings are real

The container: the biggest item, and the easiest to remove

It accounts for half the budget of a terrarium bought new. Yet a second-hand container works perfectly well:

• a wide jam jar, with its screw lid;
• a clip-top jar with a rubber seal, ideal because it really does close;
• a carafe or a demijohn with a stopper;
• a disused aquarium covered with a sheet of glass.

Three conditions: the glass must be clear and untinted (coloured glass filters out the light the plants need), the container must close properly for a closed terrarium, and it must hold at least 5 litres — below that the balance is unstable and the terrarium will ask for more attention, not less.

Wash it in hot water, without detergent, and rinse thoroughly.

Tools: unnecessary at the start

For a wide-mouthed jar, a long-handled spoon and a pair of fine scissors do everything. You already own them. A well-rinsed spray bottle you already have replaces the mister.

Tools only become necessary when the neck narrows — a demijohn, a bottle. At that point they are not optional: you cannot plant at the bottom of a narrow neck by hand.

Plants: take cuttings

A stem of fittonia, ficus pumila, peperomia or soleirolia roots within two to three weeks in the humidity of a closed terrarium. If someone you know has one, ask for three cuttings.

Otherwise, buy one plant and multiply it: a single fittonia easily gives three cuttings.

Where you should not economise

The substrate

This is the item not to skimp on. Shop-bought compost and garden soil hold far too much water under glass, compact within a few weeks, and bring in mould spores to an environment where nothing keeps them in check.

An airy terrarium substrate costs a few euros for the quantity you need. Saving money there means buying a waterlogged terrarium three months down the line — see Terrarium too wet.

If you want to mix your own: coir, fine bark and perlite, in roughly equal parts. Never compost on its own.

The drainage

Two to three centimetres at the bottom, with a separating layer on top. Rinsed river gravel will do if you have some, but the layer has to be there — the container has no drainage hole. See Clay pebbles or pozzolan and The different layers of a terrarium.

The volume

Choosing a tiny container to save money is a false economy. Below 5 litres the humidity swings too quickly, and the terrarium demands constant attention.

A build under 30 €

Supplying the container, spoon, scissors and spray bottle yourself:

False economies

Garden compost. Covered above: it is the leading cause of failure.

Moss gathered in the woods. Free, but it brings mould and pests into a closed environment — and collecting it is regulated. See Can you take moss from the woods?.

A container that does not really close. It will behave like an open terrarium, and the tropical plants you put in it will dry out.

Too many plants at once, to "fill it up". They crowd each other, and you have to take some out after six months. Three well-placed plants are worth more than six squeezed in.

Going further

The full breakdown of prices, including for a build bought new, is in How much does a terrarium cost. The kit-versus-separate-purchases comparison is in Terrarium kit or separate purchases, and the annotated equipment list is in DIY terrarium: the equipment you need.

Sources

• DIY bottle terrariums make great projects, gifts — University of Illinois Extension
• Creating a Closed Terrarium — Penn State Extension