Gardening: Pot plants to pick and mix: Make artful use of pots and tubs, and enjoy infinite variety in your garden, says Anna Pavord

The collection of pots by the back door has grown to 32. I counted them for the first time today, and the number came as rather a shock. They must have been breeding secretly in the night. Some are very small, I hasten to say, five-inchers with various kinds of tulips in them. They have been sitting in the cold frame through the winter and I bring them up to a wire stand by the back door when they come into bud.

Three pots of Tulipa chrysantha are filling the stand at the moment, neat tulips, no more than seven inches high, with long, elegant buds. The backs of the three outer petals are washed over with a rich, dull red, most intense at the centre, fading off to a fine yellow round the edge. When the sun shines they open up to show pure, buttery-yellow insides. When they are open, the outsides look striped, the red backs of the outer petals alternating with the solid yellow of the inner ones.

Tulips are more successful growing in pots than in my heavy, damp soil. When the flowers finish, the pots go back in the cold frame until the foliage has died down. Then they can lie on their sides (with the bulbs still in them) to bake through the summer. In autumn, you just stick the pots upright again so they dampen with the rain, then feed the tulips as they emerge.

Other old 8in and 10in terracotta pots are stuffed with wallflowers, more for the smell than the sight. These will go on the compost heap when they are finished. One round, fluted pot I bought for about 20p in Turkey has a single, fat double-daisy plant in it. It fills the pot completely, pushing up wave after wave of icing- pink, powder-puff flowers. There are 14 out at the moment.

This is the easy way to manage pots. You just pack each one full of whatever you fancy - tulips, wallflowers, lilies, agapanthus, petunias - then shunt the pots round in different combinations, depending on what is in flower. You might group pots of wallflowers with a few others of the brilliant red Tulipa praestans 'Fusilier'. This is a superb clear red that combines well with the tawny colours of wallflowers.

Or you might try a more complicated liaison of colours, using 'New Design', a Triumph tulip, orange- yellow, flushed with pink and green. It sounds vile but is magnificent with dark mahogany wallflowers.

Later on in the season, you can use lilies in the same way, raising them in pots in some hidden part of the garden, and then wheeling them into the limelight when they are ready to face it. Like tulips, lilies grow well in containers, and since - again, like tulips - they have little to offer when they are out of flower, keeping them portable is an advantage.

The pots by the back door have multiplied, I suspect, because it is the part of the outside that I see most of, coming in and out of the house. But there is no possibility of permanent planting there. Paving stones butt against the house walls, so there is no earth, no place for climbers. In this situation, pots are great allies, and, by manipulating clusters of smallish ones, you make sure the treats happen where you can see them. Elsewhere, you might use pots differently. If there is one large pot in a prominent place, you might think of it as a miniature garden in which you could mix plants as you would in a flower border. This is a more difficult trick to bring off. You need to think not only about colour combinations but also about the way each plant grows and its relative vigour.

Grey-leaved Helichrysum petiolare is a stalwart in pots, though it needs trimming from time to time, if it is not to swamp more cautious plants. Try it interlaced with the blue Convolvulus mauritanicus, which, like morning glory, fades to mauve as it dies. Ivy-leaved geraniums are also naturals because the foliage is strong and chunky and so makes a pot seem well filled. They drift elegantly over the edges of containers, too. There is no shortage of good ones: 'Alice Crousse', with large cyclamen-pink flowers, 'Amethyst', a semi-double pale-purple variety, 'Madame Crousse', a bright-pink double, 'Yale', a rich-red semi-double. Use them with petunias and add height, if you want to, with a fuchsia in the middle.

Phormiums, the New Zealand flaxes, also make good centrepieces for pots, especially where they are used in a modern setting and combined with foliage plants that are equally architectural. The monster varieties arch out gracefully as they grow, and you could push in a variegated agave underneath, together with an unusual fern, such as the hare's foot fern, Polypodium aureum 'Mandaianum'. If you feel you need colour, add busy lizzies.

All these, even the agave, will put up with shade. In sun, the options are greater. Certain plants crop up again and again in pot mixes: verbena, lobelia, argyranthemums. These are all plants that flower over a long season and seem to be as happy growing in pots as they are in the open ground. Some gardeners are very sniffy about lobelia, but it is not lobelia's fault that it is so often used with white alyssum as a polka-dot path edging. It has other qualities that it is not always allowed to show, and the trailing kinds weave their way undemandingly through a wide range of neighbours.

In a pot, it works with white osteospermums and lime-green hostas. It is excellent with the fine, grey-leaved plant called Lotus berthelotii, which droops very satisfactorily over the edges of containers. Mix these two with the small, lime- green flowered Nicotiana langsdorfii.

A pot is a good way of emphasising the importance of a plant in

a mixed planting. If you have a slightly sleepy sea of greys and whites and pale greens in a bed, you can introduce a pot into the middle of the planting, with perhaps a melianthus or a yucca or a cordyline in it. It adds drama and the pot lifts the plant on to a different level.

But a plant used in this way needs to be a good specimen, well grown. Putting it in a pot draws extra attention to it. It has the same effect as framing a picture.

In a shallow, wide container, you need different kinds of plants. The bright-blue daisies of Felicia pappei work well in this context, contrasting with a free-flowering rock rose such as Helianthemum 'Wisley Primrose'. The felicia is never as free- flowering as you would wish. If this bugs you, use the swan river daisy instead.

There is an advantage in using a loamy compost, such as John Innes No 3 for filling pots. The weight that makes it a pain to hump home from the garden centre is an advantage in pots; it makes them more stable. I use a slow-release fertiliser, such as Osmocote, round about now, sprinkling it on top of the compost in the pots. It lasts six months, breaking down very slowly to supply everything the plants need by way of food through the summer.

Jim Keeling's terracotta pots are available from the Whichford Pottery, Whichford, Shipston-on- Stour, Warwickshire CV36 5PG. He will also be selling pots at Arley Hall, near Northwich, Cheshire, this weekend (10am-5pm). Pots and Pithoi import pots from Crete and you can see thousands of them at The Barns, Turners Hill, West Sussex RH10 4QQ (daily, 10am-4pm). You will also find them at the Bressingham Plant Centres at Dorney Court, Dorney Village, near Windsor, Berkshire (daily, 10am-5.30pm) and at Elton Hall, Elton, Peterborough, Cambridgeshire (daily, 10am- 5.30pm).

(Photograph omitted)