A terrarium on your desk: format, light and care

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 3 litres the balance turns unstable and the terrarium starts asking for attention — exactly what you do not want at work; 5 litres is recommended for a first terrarium. 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 as soon as the window faces south or west.

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