Taking cuttings lets you refresh a composition with a plant you already know. It is not the same thing as pruning a terrarium: pruning corrects the shape, while cuttings aim to produce a new plant that can stand on its own. Not every pruning offcut is usable.

Choose a method to suit the plant

Start with fittonia, which is simpler to follow than an unidentified species. Keep a label with the name and the date: two similar-looking leaves can come from plants with very different needs.

Set up a small, clean workspace

Get together clean, sharp scissors, a small drained pot or a clear container for water, a light growing medium, and a clear box if you need to hold the humidity. Clean the tools between plants, especially if one has symptoms.

Do not use a stem that is soft, blackened at the base or covered in pests. Taking your cutting from a healthy area does not guarantee that a sick plant is trouble-free. Keep these attempts away from the main terrarium.

Take a stem cutting

1. Choose a small healthy shoot, not in flower, with several leaves and at least one usable node.
2. Cut cleanly below a node, without crushing the stem.
3. Strip the leaves that would sit in the water or below the surface of the medium.
4. Keep a few upper leaves; a large mass of foliage loses water before any roots exist.
5. Put the cutting into its rooting medium promptly, without burying the whole stem.

A few centimetres may be enough for a small fittonia, but where the nodes sit matters more than any standard measurement. Rooting hormone is not always needed; do not add it as a matter of course for every species.

Water or growing medium?

Rooting in water

Glass lets you watch the roots appear. Keep the leaves out of the water, clean the container and change the water when it turns cloudy. Roots formed in water then have to adapt to a solid medium. Avoid letting a long, fragile tangle develop before you transplant.

Rooting in a medium

A small pot with a light medium allows a more direct transfer later. Moisten it without soaking, and keep air around the forming roots. Sphagnum is one option for certain uses, not a requirement.

A clear box can reduce drying out, but it must not sit in the sun. Open it to inspect and adjust the ventilation if the foliage stays permanently wet. A cutting that is rotting does not need yet more humidity.

Recognise recovery without disturbing the roots

The timescale varies with the species, the season, the temperature and the light. Look for branching roots and new growth, rather than tugging at the stem every day. A leaf still green a few days after the cut does not prove rooting: it may be living temporarily on its reserves.

A black, soft base is reason to take the cutting out. If the upper part is still healthy, you can try a fresh cut with a clean tool, with no guarantee of success. Clean the container before starting again.

Moving into the terrarium

Make a small hole, set the roots in without bending them sharply, then gently draw the substrate back around them. Keep the collar at the right level. Do not flood the jar to "settle" the soil around the roots.

Acclimatising plants helps you avoid combining a change of medium with a change of humidity. Keep a few spare cuttings in separate pots instead of overloading the composition straight away.

If you are starting from scratch, choose identified terrarium plants. A set of fine tools makes handling easier; it is no substitute for looking closely at the stems and the roots.

Sources and scope of this advice

• University of Nevada Extension — Propagating houseplants: propagation by cuttings and by division.
• NC State Extension — Leaf, cane and root cuttings: how the methods differ from plant to plant.

This method covers common tropical foliage plants, not every species sold as a miniature. Generated illustration, for editorial purposes.