Box of tricks: If you thought window-boxes were just for pubs, think again, says Anna Pavord

Pubs are the places to see brilliant window-boxes and hanging baskets. Perhaps beer dregs make the plants flourish. Or the hot air produced by saloon-bar regulars. Lobelia is the common ingredient in most of the plantings: dark-leaved, dark-flowered lobelia with white petunias, pale blue lobelia with deep red geraniums and silver fern. Hackneyed, you might feel, but these combinations are difficult to beat.

For summer window-boxes, you need flowers that have the same unflagging determination to perform as the young Shirley Temple. Geraniums, often coaxed into bloom before they go on sale at garden centres, are supreme in this respect. Their variety means that you can easily furnish window-boxes with nothing else: trailing ivy-leaved geraniums for the front, multi-bloom types for the bulk of the planting with a few variegated types interspersed for contrast. Many-headed geraniums, such as the 'Balcon' series, give a much fuller effect in window-boxes than geraniums with heads like boxing gloves. To flower most abundantly geraniums need sun, but a window-box in full sun is more difficult to manage than one in part shade. Compost dries out faster, watering may need to be done twice a day.

A window-box looks best if it fits as exactly as possible the size of the window. Small plastic containers balanced on large sills have an uneasy, we're-not-stopping feel to them. Made-to measure wooden containers are ideal. You can line them with heavy-duty black polythene, with a few holes punched in the bottom. The bigger the container and the larger the volume of compost, the easier it will be to keep.

Painting wooden boxes can trap you in a tyranny of annual repainting. Woodstains are less demanding and, watered down, give you some pleasantly murky greens and blues. Let the plants boss the box rather than the other way around.

Profusion is the effect that you want, but in a window-box you won't get it without a dedicated regime of feeding and watering. Slow-release fertilisers (I use Osmocote Controlled Release Plant Food) are excellent for this kind of gardening. So are water-retaining gels, which sop up water faster than sponges and then release it slowly as the plants need it. Both these can be mixed into the compost at planting time.

Plastic boxes are cheap, but are not always sturdy enough to take a full load of compost. They start buckling in the middle and sag outwards in a dispirited way. Whatever you use, make sure it is securely anchored. If you are very lucky, your house may still have the ornamental cast-iron surrounds of the late 18th and early 19th centuries originally made to fence in window-boxes.

Often boxes look better from the outside than they do from in. Flowers naturally turn towards the light, so from inside, you are backstage, as it were, looking at the supports rather than the painted backdrop. You can get over this by dropping the level of the window-box slightly, so that you look down on your flowers, but whether this is possible depends on the type of windows and sills that you have.

For a suitably lush effect (and window-boxes must be lush - nothing looks meaner than a mean window-box , its plants as distant as oases in the desert) you need plenty of leaf. Include at least one good foliage plant in each mixture.

Helichrysum petiolare is a natural, because it is not too bossy, threads itself about well, climbs and cascades. The standard version has grey, felted leaves, but there is a good lime-coloured variety 'Limelight' and a cream variegated one as well. The grey-leaved one loves heat and will not flag in a sun-baked position. The sulphurous one is better in part shade. Use them with marguerites ( Argyranthemum frutescens), white petunias and shrubby santolina, with perhaps some variegated ginger mint binding the whole cast together.

An average-sized window-box, 30-32 inches long, may accommodate a dozen plants, perhaps four each of the marguerites and petunias, one helichrysum, one santolina and two ginger mints. This will give a cool effect, lost though if you live in a white painted house. White flowered window-boxes look best set against grubby stone, especially the dark grits and granites of the north.

Grey helichrysum also looks good weaving its way round ivy-leaved geraniums, such as the pale pink 'Madame Crousse' with a mixture of lobelias stuffed into the gaps. 'Cascade Mixture' trails elegantly and has flowers in a wide range of colours. Add some deep purple heliotrope if you want an extra benefit from your window-box. It smells gorgeous.

For a much warmer effect, use the greeny-yellow helichrysum 'Limelight' with a golden variegated ivy and some brilliant yellow and blue pansies. These need regular dead-heading if you want them to give a long display, but they are reliable flowerers and have the sort of squidged-up faces that always make you smile. Ivy is very slow growing, so you will need to splash out on some decent-sized plants. They are at least perennial and with care, could be with you for several seasons. If you get tired of them in a window-box, you can pot them up and use them inside.

Nasturtiums are also plants that raise the spirits. There is nothing restrained about a nasturtium. It is a helter-skelter opportunist and will probably swamp any plants that you put with it. Use it on its own, sowing seeds direct into the window-box. If it is too soon to get rid of your spring display, raise nasturtium plants in pots inside, planting them out at the end of May. 'Alaska' (Thompson & Morgan 1.99) has leaves splashed and mottled with cream. If you want a more compact nasturtium, a new variety 'Princess of India' (Thompson & Morgan 1.99) makes bushy plants with dark foliage and deep red flowers.

I've ordered plugs this year for a short cut container of blue surfinias (five plugs for 5.95) mixed with the beautiful grey-leaved trailing plant, Lotus berthelotii (five plugs for 5.95). The foliage is the real point of the lotus, but towards the end of summer it produces parrot-beak flowers of a rich brownish-orange. With a smattering of trailing lobelia, there I am. Sorted.