House plants are no longer in vogue. Yet, now we need them more than ever for the sake of our health. Indoor air in the modern home is, well, polluted. Not as bad as standing on a traffic island in Causeway Bay but certainly far from pure. Air conditioning may draw outdoor pollutants in, but it doesn't expel them. They mix with emissions from plastic, synthetic furnishings, finishes, solvents, carpets, photocopiers, printers and building materials, to name just a few sources of nasties in the home. “We use a whole lot of materials derived from fossil fuels that contribute to pollution, like furniture, paint and computers,” says Professor Margaret Burchett from the University of Technology Sydney, which tested the ability of indoor plants to reduce volatile organic compounds (VOCs), carbon dioxide (CO2) and carbon monoxide (CO). “There's also more carbon dioxide as we all breathe together.” Plants work with the potting mix to achieve the removal of pollutants remarkably quickly, while replenishing the oxygen in the atmosphere. The efficiency of this natural system is not diminished by night – it is working for you 24/7. So we need each other. We take in oxygen and expel carbon CO2; plants absorb CO2 and release oxygen. As a bonus, the reduction of CO2 improves concentration, so you remember who's who in Game of Thrones . The larger the plant, the greater CO2 absorption. The underside of the leaves helps balance the humidity in the home space. Plants are also thought to reduce stress and anxiety levels. Although as few as three plants can make the significant difference, as interior decorating items, individual pots have fallen out of favour. Indoor gardens are the thing. Finnish firm NaturVention specialises in wall gardens, sometimes known as vertical gardens or living walls. CEO Niko Järvinen says that they “naturalise the air” and advises against flowering plants because of allergies. The plants are potted in tubes with water stored at the base of the wall. Maintaining the system is hi-tech. “When we bring a wall to any place, it’s able to find the right settings, it senses the air temperature, humidity and so on,” Järvinen says. Connected to the cloud, the garden is smart-controlled. You don't need to bring in the experts from Finland. Neither do you have to cover an entire wall. Vertical gardens of succulents have been created in picture frames which are taken down and watered once a week. A series of small picture frames with air plants and some decorative pebbles is effective. Herb gardens have been made from rows of guttering attached to the wall and a drainage system. Most landscape gardeners would be able to do a vertical garden on a wall or part of a wall. You could do it yourself but that might be too much of a challenge when it came to watering, fertilising and draining. The basic wall garden is a frame affixed to the wall, backed by plastic sheeting. A medium through which the plants can grow roots is then attached – felt or hessian. If you decide to DIY, the easiest way is to buy the “garden” frame from your hardware store or online. Take expert advice on your watering system. You could also source a product called Greenwall pockets. Each pocket, 600mm x 400mm, has four pouches to hold as many as 16 plants. More conventionally, you could create an indoor garden. It does not have to be on the floor but it should be near a good source of light. Think in terms of a hanging garden, with glass holders strung up at different levels. Or use a garden trough as a room divider. You could even have a trough on wheels, to be placed wherever your interior decorating impulse dictates at the moment. Succulents are the easiest plants to care for but they are not your first choice for indoor air purification. You should ideally look for green leafy plants, and some of the most easily obtainable varieties are the most effective and the most attractive. The Peace Lily is known for its dark green leaves and white flowers. It is easy to care for and is recognised by space agency Nasa for its air-purifying capabilities. You could put one or more in your bathroom as they like shade and are effective against mould. Another old favourite, the spider plant, is a fast antidote to polluted indoor air. As it reproduces by throwing out “babies” on long spikes, it looks great as a hanging plant. It reproduces so well you'll be begging friends to take the offspring. Dracaena, known as happy plants or dragon trees, are great for indoor life. Research shows the happy plant removes formaldehyde, benzene, toluene and xylene. The aspidistra, the weeping fig, philodendron and Zanzibar gem are all tough plants which do an excellent job of air purification. This is especially so if you have recently renovated or put down new flooring. Although less attractive to some people, but with a certain architectural quality which makes it a good foil in a group of plants is sansevieria, known as snake plant or mother-in-law's tongue. Finally, in season, buy lots of pots of cyclamens in different colours. Not only do they do good work for your health, their beauty does a lot for your psyche as well.