Think before you buy

When you are choosing a house plant you need to decide whether you want a permanent plant with attractive foliage all year round or a short-term flowering plant that is thrown away after flowering. Think about how much effort you're prepared to put in. Some plants are easy to grow while others require very controlled conditions for their survival (see box). Although plants can be bought all year 'round, you shouldn't buy rare or expensive ones in winter. If you buy them between spring and mid-autumn they will settle in before the dark, cold days of winter.

Not just for Christmas

Many plants you bought or were given for Christmas will be looking very sad at the moment. Plants such as Christmas pepper, poinsettia and chrysanthemums will have been specially forced for Christmas. For instance chrysanthemums are sprayed to keep them short - in the wild they grow up to five feet tall. Because they've been sprayed and forced they probably won't survive and should be thrown out. But some plants will survive.

Azaleas won't fail you

Azaleas should be over wintered in cool conditions and then re-potted in lime-free compost. Stand them outside from early summer to autumn. When flower buds appear, bring them back inside and they will flower for Christmas again. Plant hyacinth bulbs out in the garden. They may take a year to recover but will eventually flower in early spring.

Preserve that poinsettia

People tend to over-water poinsettias - and all Christmas plants - which makes the bottom leaves fall off, leaving just the tall red bracts (coloured leaves). If you want your plant to flower again next Christmas, cut the stem to about 4in from the bottom of the pot when the leaves have fallen back. Keep the compost almost dry and put it in a mild, shady area. Start watering it again in May, give it a liquid feed about once a fortnight and repot it, and the plant will produce new growth. In September cover the plant with a black polythene bag at around 3pm each day and keep it in total darkness for 14 hours. If you do this every day for about eight weeks the poinsettia will bloom for Christmas. It will be much taller than the original plant because the chemical that was sprayed on it to keep it short will have worn off.

Keep the right heat

The two main factors that determine whether any plant will survive are light and temperature. Fluctuating temperatures are lethal to houseplants. Most plants will survive in a cool 5055F while more tender and exotic species need a minimum of 60F. The top of the television is the worst place for plants because it changes temperature as it is switched on and off.

Bright, but not breezy

Houseplants thrive in indirect sunlight while full sun can burn thin, delicate leaves. Some plants will grow in semi-shade but full shade is not suitable for any plant. All plants hate draughts, which turn some leaves brown and cause some plants to droop and lose their leaves. Don't leave plants behind drawn curtains at night.

Not too wet, not too dry

Over-watering kills most plants - roots need air as well as water so you can drown them. You need to feel and observe the compost to determine whether the plant needs watering - water only when the compost dries out and use tepid water. You should water foliage plants thoroughly and often between spring and autumn when growing conditions are best and cut down on watering during winter. Plants prefer a good soak and then for the compost to gradually dry out rather than watering little and often as the water won't reach the lower layers of compost. Most plants, except cacti, hate the dry atmosphere caused by central heating. It makes their leaf tips go brown and shrivel. Create a moist atmosphere by misting the foliage with a hand mister.

Dramatic displays

A tall, solitary imposing specimen such as a palm or rubber plant can have a dramatic effect in a spacious room and act as a focal point. Small and medium-sized plants are best displayed as a group. Take into consideration form, leaf shape and colour and aim for a good combination. Adding flowering plants at certain times will brighten up the display. For ideas on good combinations look at ready-planted bowls and containers. You could plant up your own terrarium and bottle garden but water them carefully as water-logging can be fatal.

Denis McNally is the propagation foreman at the National Botanic Gardens in Glasnevin, Dublin.