Country & Garden: Pot luck in the city

Urban Jungle: Roof terraces and small backyards can be transformed by the addition of a few well-chosen planters

The city is where container gardening comes into its own. There are many urban gardens where the planting is either all grown in pots - such as roof gardens or small backyards - or where pots are used to decorate or accent areas within a garden. A big advantage of containers is that they can be moved. This keeps the garden looking fresh and interesting and allows you to move more tender plants to a sheltered spot for the winter.

When designing with planters it's important to remember scale. A common problem is a bitty garden with too many small pots. Try to use a few really big pots, which will add definition to a garden of any size. For a cohesive look within a small garden, stick to one type, and even one colour, of container rather than a mish-mash. Repetition and simplicity work; and it's the same with the plants which go in them. Nothing looks better than the rhythm of a set of identical pots containing box balls lining each tread of a set of steps.

There is a wide choice of planters available at the moment: terracotta, glazed ceramic, wooden, galvanized steel, fibreglass, plastic etc. If you have a roof terrace use lighter weight planters such as fibreglass or galvanized steel. Galvanized steel containers need to be lined with polystyrene sheets (available at any builder's merchant), otherwise the roots of the plant will cook - literally.

It is a myth that there are only a few plants which do well in containers. We buy almost all our plants from the garden centre, which are growing happily in pots. Even large shrubs and small trees can grow healthily in containers as long as they are re-potted when they run out of root space. At a nursery you'll see lots of watering and feeding going on and this is crucial for most plants grown in containers.

Silver-leafed plants will thrive in sunny areas. The Olive (olea europea) is a silver-grey evergreen, which can add a Mediterranean feel to any terrace and is well worth considering, being much hardier than you would expect (it is tolerant of -7c) as well as thriving in the well-drained conditions of a container. Olives can be bought as a small bush or standard tree and may even fruit (not to be tasted - from experience!) in more sheltered areas.

The grasses will add a real summer feel to a terrace, and rarely clash with other plants in a composition. The graceful helictotrichon sempervirens (formerly avena candida) grows to 90cm and its bright bluey-grey arching leaves will dangle down to break the line of the top of the container. Festuca glauca, blue fox, is much smaller - at 10cm it forms neat little battleship grey tufts which can help create a designed look when in small pots placed around a larger planter.

One of my favourite plants is convolvulus cneorum. This will reach 60cm high, and is a loosely-formed shrubby relative of the dreaded bindweed. Its leaves look as though they have been touched up with a silver spray can, and its flowers, white with pinkish stripes which are produced sporadically throughout the summer, make a wonderfully subtle statement against the leaf. It's also evergreen and likes poor soil - what more could you want from a plant?

In shadier areas, containers can grow many plants not normally considered feasible. Hostas can be a bit of a nightmare where slugs and snails hang out. Variegated forms such as hosta decorata Thomas Hogg with its white edge leaf, or h. fortunei Aureomarginata with its yellow edge, will always help brighten a dark corner. Mulching with fine grit or smearing Vaseline around the top of a pot should keep the enemy off.

Plants which require different soil from that which your planting areas have to offer - such as the acid loving plants - can be given the right soil conditions in a pot. Camellias, azaleas and maples all like to be planted in ericaceous compost and like a shady sheltered spot.

If you have an exceptionally nice pot and can't find a plant to complement it, you could push the boat out by leaving it completely empty! Why not?

Joe Swift is a garden designer and owner of The Plant Room, 47 Barnsbury Street, London N1 1TP (0171 700 6766)