When Professor Tove Fjeld from the Agricultural University of Norway placed a big tray of houseplants in a classroom recently, the effect was dramatic. Pupils using the room reported a 45 per cent drop in the number of headaches and sore throats. They also had fewer problems staying awake and felt more positive and less tired.

When Professor Fjeld asked the teachers how they felt, they reported much the same, and said the classroom felt more relaxing. “Teachers work in a far more polluted environment than office workers, and often complain about poor air quality,” says Professor Fjeld. “Ventilation in classrooms is typically poor, and there are far more people concentrated in one room all day than you’ll ever find in an office.”

Professor Robert Davies from the British Allergy Foundation says: “Indoor air pollution is becoming more of a problem to asthmatics and allergy sufferers than outdoor pollution.” The amount of time we spend inside is one factor. Ozone emissions from computers, fax machines and photocopiers are the major sources of office pollution, while nitrogen dioxide (from burning gas) and vapours from carpet underlay and synthetic furnishing hang in the air at home.

The World Health Organization has found the chemical concentrations in energy-efficient buildings are up to 100 times greater than background levels, with carbon monoxide, benzene, methane, nitrogen oxide, acetone and formaldehyde being just some of the atmospheric irritants.

“Classrooms also have a lot of dust,” says Professor Fjeld. “Some comes from school books and chalk, but most of it comes in on children’s clothes. In Norway we’re teaching them to leave their outdoor clothes outside and change their shoes. In urban areas the dust is full of particles covered in oil products from roads - this is very irritating to the airways.”

The British Allergy Foundation says the presence of such pollutants is one of the causes of the huge rise in asthma over recent years. Some of the problems that may be caused by poor air quality at school and home include dry, itchy skin and eczema, headaches, tiredness, asthma, eye, nose and throat problems, and congestion of the nose and throat. Schools are at least draughty, which helps clear out stale and dirty air, but energy-efficient homes can develop a heavily polluted atmosphere. In either case, any of the above symptoms might be helped by something as simple as a houseplant.

NASA has tested 50 plants for their ability to remove toxic gases from sealed test chambers and has found that they are able to suck up gases and airborne toxins. A spider plant, for example, can absorb 96 per cent of carbon monoxide (from exhaust fumes) from a sealed chamber, as well as soaking up formaldehyde, a common household vapour. And the longer plants are exposed to toxins, the higher their absorption rates. “They also work as mini vacuum cleaners,” says Fjeld. “They release humidity which binds to dust, creating a micro-environment that reduces irritation to mucous membranes. And they provide huge horizontal leaf areas on which dust settles.”

The question so far has been whether plants can be of use in a practical setting. You’d need a veritable jungle to make an impact on the carbon dioxide expelled by 30 living, breathing pupils, but they might have perceptible effects on air quality. “Research from Australia has confirmed that plants can be powerful air purifiers even when concentrations of chemicals are low,’ says Professor Fjeld. “The human body is a fine instrument, able to detect changes in indoor air quality far below guideline concentrations - even small changes in the chemical constitutions of air may influence health and comfort.” So, put a plant on your desk: if nothing else, looking at it will cheer you up.

ANY COLOUR YOU LIKE

Plants or fresh flowers could you give you an added mental edge. Researchers have established that being near green things can have a profound effect on well-being.

Workers who can see green areas through the window report less stress than those with a view of the netball court and parking lots. Hospital patients recover faster with fewer post-operative complications and with less frequent and less powerful medication if they have a houseplant beside them. And university students who look at pictures of nature feel less anger and fear than those who look at man-made environments.

“Even fairly brief visual contact with plants might be important for promoting restoration from the detrimental effects of commuting, work pressures and the other stressors most urbanites encounter daily,” says Roger Ulrich director of the centre for health systems and design at Texas Aamp;M University.

So it’s official, plants aid concentration, help memory and encourage positive thinking - all making them something to recommend for your desk.

Cut flowers and window boxes also allow you to harness the powerful subliminal effect of colour.

“We respond to what we see and even a brief glimpse of flowers while you work can change how you feel,” says Ingrid Collins, consultant educational psychologist at the London Medical Centre, a Harley Street private practice. “When you go to buy flowers the colour that really gets to you is by definition the colour that you really need.”

Here’s her guide to the spectrum:

* Red anthuriums, celosia (cockscomb), heliconia, roses, geraniums, amaryllis, bromeliads.

Good for focusing and energising. Not good for classrooms - children aren’t short of energy and red can encourage aggression.

* Orange heliconia, calla lily, asiatic lily.

More calming than red, but still energetic and stimulating.

* Yellow gerbera, tulips, daffodils, sunflowers, solidago (golden rod).

Good for the intellect, yellow is a great restorer of the mental faculties if you’ve had a challenging day intellectually.

* Green as well as grass and foliage, breeders are developing many varieties of green flowers: try shamrock chrysanthemum, kermit chrysanthemum, green carnations, ‘Viburnum opulus’.

These can put you back in touch with yourself if you’ve been emotionally challenged. Green is the centre of the spectrum and the predominant colour of nature - it will take you away from the cares of day, and is very refreshing.

* Blue cornflowers, eryngium, iris, hyacinth, agapanthus, delphinium, campanula.

Restful and calming, after busy practical days.

* Pale lilac gladiolius, lisianthus, liatris, lilac phlox, orchids.

A meditative colour that moves the mind’s higher inspirational regions.Good for planning and conceptualising.

* Pink oriental lilies, amaryllis, sweet-peas, azalea, kalanchoe, pink stock.

Good if you’re suffering compassion fatigue, after a day with demanding children. Inspiring and comforting if you feel you’ve given out all your love.

* White oriental lily, white lisianthus, white anthuriums, ornithogalum.

Good for total refreshment. White gives everything, says Ms Collins, and is generally restorative. If you’ve had a hard day it will help clear your mind.

* Combinations: “Orange and green flowers are best for day-to-day marking because they bring energy and intellect,” says Ingrid Collins. “Yellow, blue and green are good for classroom and kids. Yellow to stimulate the mind, and blue for communication.”

HOME-GROWN SOLUTIONS

Studies show houseplants are an effective, low-tech antidote to indoor ozone - one hazard of hi-tech living. NASA has tested the ability of plants to remove toxic gases from sealed test chambers. The top performers are:

* Rubber plant (‘Ficus elastica’ ‘robusta’). A good all-round detoxifier, particularly effective at removing formaldehyde, a common irritant among household vapours. High rates of photosynthesis make it good for stuffy rooms. Bred for toughness, can cope with dim light and cool temperatures. Feed regularly through summer, allow to dry between watering, mist often.

* Spider plant (‘Chlorophytum comosum’). Ideal for rooms on busy roads: removes carbon monoxide (from exhaust fumes) and formaldehyde from the air. Almost impossible to kill: spider plants are easy to propagate. Semi-sun to semi-shade. Feed regularly.

* KentiaHowea palm (‘Chrysalidocarpus lutescens’). Chases away toxins and releases a lot of moisture into the air - colds and allergy attacks are often aggravated by low indoor humidity. Needs semi-sun. Keep rootball damp, fertilise regularly during the growing period, mist regularly.

* Dracaena ‘Janet Craig’ (‘Dracaena fragrans’ ‘Janet Craig’). Prized as an office plant for its ability to soaks up trichloroethylene, a chemical released by photocopiers and printers. Long-living, it does best in semi-shade. Fertilise every two weeks in summer and water less in winter. Mist often.

* English ivy (‘Hedera helix’). Excellent overall rating in detoxing tests, particularly good at removing formaldehyde. Prefers semi-sun. Allow to dry between watering, but don’t push your luck. Mist often to avoid spider mites, which suck the plant dry.

* Boston fern (‘Nephrolepis exaltata’ ‘bostoniensis’). Excellent for removing formaldehyde and restoring moisture. But it’s a high maintenance plant: needs frequent misting and watering, or leaves go brown and droop.

Care advice provided by the Flowers and Plants Association. Tel: 0171 738 8044. Website: www.flowers.org.uk