It's not just a question of pot luck

Putting a plant in a pot has the same effect as putting a frame round a picture. It focuses the eye and sets the object apart. Neither pots nor frames should overwhelm. If you have a pot of decided character, it may be more satisfactory to let it stand alone. Filling it with flowers could be as indigestible as cramming two puddings into one lunch.

Pots provide a quick-fix solution to several gardening problems. They allow you to grow plants in places such as balconies and roof gardens that have never had a sniff of real soil. At ground level, where earth may have been supplanted by concrete and tarmac, well-planted pots give an illusion of fecundity and growth.

You can also use them to give instant lift to borders. This is how I use lilies. I mostly lose them if I plant the bulbs in the ground. I suspect small black keeled slugs are the problem. Planted in pots, the lilies bulk up and prosper and can then be plunged into the middle of patches where less is happening than it should be.

Pots are also dangerously addictive, as anyone who has them will already know. One on its own acts as a magnet, for they are by nature clusterers. And what better to set off a fine fuchsia in a pot than a clutch of other pots round its base, filled with a complementary mixture of pelargoniums, helichrysums or the blue daisy flowers of felicia.

This is one way you can get round the problem of not having pots that are big enough, on their own, for mixed plant-ings. The watering is more difficult, as smaller pots dry out very much more quickly than big ones. But sempervivums (the round flat fleshy rosettes called house leeks), which do not like competition from other plants, are best grown on their own in small, low pots. Then they can be grouped with succulents such as waxy aeoniums and pots of laurentia.

Laurentia - like felicia - is a container plant that has suddenly come out of nowhere fast. I grew it in pots last year, partly because I liked the blue, star-shaped flowers, but also because the foliage is so good. It is dark and deeply cut. The disadvantage is that the plants, left to themselves, are very slow to come into flower. It was August before they made anything of themselves. Full grown plants, bought at a garden centre, will have been pushed on faster than I pushed my plants, which were set outside in mid-May.

Cunning gardeners, with greenhouses and conservatories at their disposal, start making up their pots under cover in mid- April so that by the time they go out, the plants are well advanced in growth. But you need a trailer or a strong back, or both, to shift them from the inside out. You also need a lucky break with the weather. Plants grown inside develop in a softer, fleshier way than they do outside, where hail, heavy rain and wind can tear them to bits.

Paul Williams, who plants up fabulous pots in the garden at Bourton House, Bourton-on-the-Hill, Gloucestershire, always uses plenty of good foliage in his containers. That, more than flowers, he says, is what makes them look rich and exotic. With a rich abutilon, such as 'Ashford Red' he uses cannas, sprawling bidens, which like laurentia, has excellent foliage, and then adds a few more unusual touches, such as pale apricot Mimulus aurantiacus and orange-red cigar flowers (Cuphea ignea).

On its own, the mimulus is a scraggy grower, but thrown in a melee with other plants, its straggling habit is disguised and you can admire it extravagantly for its strangely coloured flowers. It is very good with the acid-coloured helichrysum 'Limelight', but helichrysum is one of the top 10 plants for containers, good with most things. Sometimes it tries to swamp. Then you need to be ready with secateurs to stop it taking over. 'Limelight' is better in shade than in sun, when it tends to scorch.

Begonias are not most people's first thought for containers, but Paul Williams uses them brilliantly. He's particularly fond of B. sutherlandii, a South African species with long, slender trailing stems, and lopsided bright green leaves, often veined with red. The flowers are small, but they are produced in hanging bunches, the same smudgy, chalky shade of apricot orange as the mimulus. Both look good with the lime helichrysum.

I'm also very keen on Begonia fuchsioides. Its name tells you what to expect. It's a begonia pretending to be a fuchsia. It can grow up to three feet tall, with strong, reddish coloured stems. The foliage is tiny and very glossy. And the foliage is all you will get, if you use this as a container plant, for the flowers come during the winter, hanging panicles of pink and white.

Because its habit is so upright, B fuchsioides, like the abutilon 'Ashford Red', is best used as a centrepiece in a biggish pot, with other plants grouped around it. Try it with scrambling silver-leaved Convolvulus althaeoides and the ever-obliging lobelia, another of the container top 10. The 'Cascade' series of lobelias is first choice for hanging baskets, but it is equally good in pots too, dripping out over the sides to give the feeling of abundance that is the keynote of all the best planted pots.

Another Williams trademark is the use of herbaceous perennials in containers. Crocosmia, for instance. It's not an obvious choice for planting in a pot but, as he points out, the sword-shaped foliage does the same job as the New Zealand flax, or phormium. The flowers, at the orange-red end of the spectrum, blend naturally with nasturtiums swirling around below. Mr Williams, of course, does something far more sophisticated than that. He grows crocosmias in pots with hedychiums (ginger lilies) to produce wildly jungled effects.

You are also more used to seeing the striped grass, Hakonechloa macra 'Aureola' in borders than in pots, but like all grasses, it has great grace and can be used as an arching centrepiece in a biggish pot. The stripes are bright green and yellow, so you need to think carefully about what is to go with it. White is safe, and the underplanting could be of white-flowered petunias. Alternatively, you could build on the yellow note, and add daisy-flowered Coreopsis vertillicata, either lemon yellow 'Moonbeam' or the usefully drought-resistant 'Zagreb', which has rich golden-yellow flowers. The foliage is finely cut.

Mr Williams often uses another grass, Molinia caerulea 'Variegata', in pots. It's taller than the stripy hakonechloa, and the spiky flowering heads are held well above the foliage, which is, again, striped, but much more subdued than hakonechloa. If you like subdued plantings, use it with purple-leaved clover (Trifolium repens 'Purpurascens Quadrifolium'). If you think it needs lightening up, plant it with variegated felicia or blue-and-white nemesia. The oddly named nemesia 'KLM' (Thompson and Morgan pounds 1.69) would be ideal.

For more planting ideas for tubs, hanging baskets and window boxes, see Paul Williams's new book 'Creative Containers' (Conran Octopus, pounds 12.99). The garden at Bourton House, Bourton-on-the-Water is open every Thursday and Friday from 29 May to 24 October (12-5pm). Admission pounds 2.50. Good pots are available from S & B Evans, 7a Ezra St (just off Columbia Rd) London E2 7RH, open Fridays (9am-5pm) and Sundays (9am-1.30pm). Other times by appointment, call 0171-729 6635.