A terrarium is the most sensible desk plant there is: it survives absences, there is no watering to remember, it makes no mess on a worktop, and it fits in 20 centimetres. Two things need attention — light, often too scarce in an office, and heat, if your desk is near a window.

The right format

Between 15 and 20 cm across for a closed jar. That is the compromise: enough volume for humidity to settle, compact enough to share the desk with a keyboard, a screen and a notebook.

Below 5 litres the balance turns unstable and the terrarium starts asking for attention — exactly what you do not want at work. Above 25 cm it takes over your working space.

Prefer a shape that is wider than it is tall: it stays put if knocked, and takes an elbow better than a narrow carboy.

Light, the real question

This is what decides success. An office is not lit for plants.

One or two metres from a window: ideal. Do not press it against the pane, above all on a south or west aspect — under glass the temperature rises very fast, see Terrarium too hot.

In open plan, far from the windows: ceiling lights almost never suffice. They light the room for reading, not for growing. The symptoms show within weeks: moss pales, stems stretch, variegated plants lose their colour.

The fix: a small grow light 20 or 30 cm away, on a timer, six to eight hours a day matched to office hours. It is discreet, inexpensive, and settles the question for good.

Which plants

The most tolerant in moderate light, and the slowest growing:

• peperomia, very steady and undemanding;
• a small fern, which takes part shade well;
• ficus pumila, tough, to be pinched every couple of months;
• fittonia, which tells you when it is thirsty — handy when you do not think about it daily;
• some moss on the ground.

Best avoided at a desk: species that want strong light, such as hypoestes, which loses its colour and turns ordinary.

What care really means

Two or three sessions a year, ten minutes each:

• prune whatever touches the glass;
• take out faded leaves;
• clean the inside of the glass.

Plus thirty seconds of watching each week: does the mist come back in the morning? If so, all is well. If it has been gone for several days, a few sprays — see Watering a terrarium.

Holidays

This is the deciding argument at work. A balanced closed terrarium goes three weeks, a month, sometimes longer, with nobody to look after it. No potted plant does the same.

One precaution before a long summer absence: move it away from the window. A closed office in August can get very hot, and glass amplifies it.

The pitfalls specific to an office

The radiator or heating vent. A terrarium just above one loses its water far faster and dries out within weeks — see Terrarium too dry.

The windowsill. Tempting for the light, often fatal for the heat.

Moving desks. Carry it with both hands, level, and never on its side: the substrate shifts and the plants come loose.

The helpful colleague who waters it. A note beside it is enough: please do not water, it looks after itself. It is the leading cause of drowning in the workplace.

Getting started

A kit covers the container and the right quantities with nothing to decide — see Terrarium kit or buying separately. The full build is in Your first terrarium: the beginner's guide.

Sources

• Creating a Closed Terrarium — Penn State Extension
• How to Design a Closed-System Terrarium — Mississippi State University Extension