Gardening: A dash of colour for the underground: Continuing her Workshop series, Anna Pavord helps to brighten up the patio of a basement flat beside a tube line

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I have a basement flat in a four-storey, turn-of-the-century block in west London. It faces south at the front and has a small patio at the back that is separated from the District and Piccadilly Underground lines by a high wall. Though facing north and enclosed on three sides by a wall and on the fourth by the house, the patio is reasonably light but gets practically no direct sunshine. One corner is shaded by next-door's lilac tree, overhanging a raised flowerbed running the length of the rear wall, which is about 12ft long by 4ft deep and 3ft high. Actually, flowerbed is a bit of an exaggeration as it contains a thin layer of poor topsoil on top of builders' rubble, and is host to the roots from the lilac tree growing next door.

My flat-mate and I bought the place five years ago and I immediately set about planting the disused bed (which seemed to serve as the neighbourhood cat-litter tray). Rather than dig down to remove the topsoil and rubble and fill it with good soil, I opted to plant in pockets of fresh soil. Maybe this was a mistake, but the only way to get things to the patio is by traipsing through the entire flat. Being a great fan of clematis, I have planted several along the rear wall ('Miss Bateman', 'Durandii', 'Hagley Hybrid' and the ubiquitous C montana), which scramble up some trellising along with an unhappy-looking jasmine. The bed, which also contains various hebes and a hardy fuchsia, is otherwise pretty much green for most of the year, apart from a sprinkling of crocuses and a few weedy tulips in the spring and an annual planting of impatiens to give some colour in the summer. Do you have any suggestions for getting more colour into the planting scheme?

NIGEL BRAND'S basement yard was not the black hole that I had imagined from his letter. The raised bed at the back faces south and the sun was travelling along the boundary wall when I visited.

Dr Brand does not usually see it because he spends his days at the Royal Brompton Hospital, where he is a research scientist. His field is molecular biology and he looks at the ways genes work in the heart. He keeps phalaenopsis orchids in an old aquarium in his laboratory.

I felt the immediate difficulty with the raised bed was that it was dominated by the vertical 4ft wall that retained it and by the boundary wall rising behind it. Both were painted cream, and although the back wall had a few strands of clematis threaded weedily through a new trellis, the blankness of these two verticals detracted from the effect that the plants in the actual bed should be making.

If these two walls could be richly covered, I suggested, the bed would be enhanced and Dr Brand would effectively have trebled his gardening space. In terms of square metres, each of the two walls was as big as the bed itself.

By the time I arrived, the lilac had been cut back so the whole yard was completely open to the sky. In terms of the way that plants grow, this is much more important than direct sunlight. There were some good key shrubs in the bed: a mahonia on the left with an excellent, purple-leaved hebe (possibly 'La Seduisante') next to it.

Then the structural planting rather fell away, some key positions in the centre of the bed having been bagged by Euphorbia robbiae (which, although a brilliant plant, merited a far less dominant position) and a prostrate juniper that looked as though it had been peed on once too often by neighbouring cats.

On the right-hand side, the bed needed some permanent planting as good as that on the left. The bed also desperately wanted feeding. I suspected that it had been made not for its aesthetic appeal but as a dump for the rubble that accumulated when the basement was converted into a flat.

Dr Brand was still worrying that he should have cleared the whole thing out and filled it with fresh soil before starting to plant. Impossible. The counsel of perfection perhaps, but not what happens in real life. Imagine carting nearly 200 buckets of soil through the bedroom, the sitting-room, the kitchen, and up the steps to the street. Then you would have to go through the whole process in reverse. But a couple of sacks of 6X or some equally bulky manure, spread at regular intervals on the surface of the raised bed, would do wonders for the fertility of the soil and complement the liquid feeds, such as Liquinure, which Dr Brand uses.

When planting, I would also be tempted to use a John Innes compost instead of a peat- or coir-based one. It has more weight and hangs on to nutrients longer than the lighter types of compost. With the soil suitably boosted, you could expect the extra planting in this bed to thrive.

The most pressing need was for a plant that could tumble down from the front of the bed to clothe the tall, blank retaining wall in front. Dr Brand had planted a few good pale greyish-leaved ivies that were being very slow to bulk up. I suggested nasturtiums, which are fast, succulent and jolly. They would provide the keynote for a display of hot-coloured flowers set off by shrubs with good evergreen leaves.

Having noticed this year how brilliantly self-seeded nasturtiums have done in an unprepossessing dark billet under a beech tree in my garden, I did not think they would be frightened by Dr Brand's basement. You need a trailing type such as 'Climbing Mixed' (Thompson & Morgan, 89p) rather than a compact, bushy type. I have also found the double, semi-trailing variety 'Double Gleam Mixed' (T & M, 99p) an enthusiastic beast.

For the back wall, to bulk up the sparse threads of clematis, perhaps Eccremocarpus scaber, which has rather attractive ferny fo-

liage, and is fast growing. In the latter half of the summer it carries spikes of orange tubular flowers - not more than an inch long but lots of them. You can get a cherry-red form as well. A good strain is 'Tresco Mixed' (Chiltern, pounds 1.16), which has flowers of gold, scarlet, orange and many shades in between. It is easy to raise from seed and in London's centrally heated climate would be perennial. For colour on the ground, I would use bright- red verbenas or English marigolds, which have both bulk and presence.

The advantage of both nasturtium and eccremocarpus is that they grow rapidly. They are neither permanent nor structural, but you can make a virtue of this by trying different schemes on the vertical surfaces fore and aft of the bed. You could use cobaea with its excellent foliage and purple bells to loop over the front of the retaining wall (it is easy to raise from seed, and fast growing) with a slower, more permanent plant such as wistaria to take over the back, south-facing wall. It would have to be carefully trained but would provide a good host for the existing clematis. A bag of manure to itself each spring would keep it cool and fed.

Within this purple-mauve matrix, enhanced by the existing purple-leaved hebe, you could plant masses of stocks for early summer scent. I grew double 'Appleblossom' (T & M, pounds 1.99) this year, not as double as it should be but deliciously scented. A thick carpet of scillas and snowdrops arranged in big billows would waft Dr Brand through early spring. A tray of large, blowsy petunias from the Columbia Road market would pick up where the stocks left off in the summer.

Thompson & Morgan, Poplar Lane, Ipswich, Suffolk IP8 3BU (0473 688821). Chiltern Seeds, Bortree Stile, Ulverston, Cumbria LA12 7PB (0229 581137).

(Photograph omitted)