Gardening: Lace, polished leather and unrequited love: In spring, the temptations of garden centres are many. Anna Pavord advises on how to resist amour fou

I NEED crampons and an oxygen mask to get to the top of our compost heap now. Over the past month I have been hauling weeds, mostly nettles and buttercups, off the bank, and there have been more of them than a gardening correspondent should admit to. The heap looks as though it is growing itself.

With the dross gone, I could see the plants on the bank more clearly - and the gaps in between. This, anyway, was my justification for several extremely satisfactory raids into foreign territory (in Dorset, anywhere more than 12 miles from base is foreign) to bring home new plants.

It is hard to resist the call of the nursery and garden centre at this time of year. There is a beguiling sensation of making a fresh start. Blinded by an optimism of the most irrational kind, oblivious to the mistakes and disasters of the previous season, mesmerised by ranks of plants, all thumping away in their pots fit to bust, you ricochet from magnolia to rhododendron, from ceanothus to chaenomeles, each new plant the centre of a new dream.

Plants that are actually in flower in their garden-centre pots are the most dangerously captivating but, for a garden that is to satisfy you in the long term, you need to look further than flowers. Think of them as extras, the icing on the cake, and assess plants by other qualities instead. What sort of habit does the plant have? What are its leaves like? Are they well shaped? Do they have texture? It is by manipulating all these attributes that you build up the best plant groups in a garden. Of course, flower colour has a part to play, too, but it is by no means the most important consideration.

Take epimediums. (Actually, I took rather more than I should have done, from Blackthorn Nursery at Alresford.) They are in flower now, white sprays on E grandiflorum nanum, crimson on E x rubrum, clear yellow on E davidii. I enjoy the flowers. They grow on strong, thin, wiry stems well above the foliage. They are delicately made, four rounded inner petals curving down, four strappy outer ones making a ruff around them.

But by the end of the month the flowers will be finished. What can the epimedium offer then to earn its place in the garden for the next 11 months? Leaves. These are held, often in arrangements of three, on thin stiff stems. The leaf at the top of the stalk is symmetrically balanced, the pair that face each other lower down are lopsided, the outer lobe of each pulled as if by gravity towards the ground.

The new leaves are almost fully formed now, replacing the old foliage that has lasted throughout the winter. On E x rubrum, the green is edged and smudged with mahogany. The shape and colour of the foliage, the high gloss on the leaves of some varieties, make epimediums good mixers. They work well among clumps of cyclamen, another plant that has leaves at least as important as its flowers. They also sit comfortably between clumps of hellebores, particularly the hand- shaped leaves of H orientalis.

But it is no use saying 'Gotta have' unless you can provide the sort of conditions that epimediums (and cyclamen and hellebores) enjoy: cool, moist soil with plenty of humus. That is the other difficult lesson to learn. Not everything that you fall in love with will love you in return.

Ferns are confident enough to dispense with flowers altogether. Form is all and, undistracted by colour, you can settle to the engrossing business of finding them suitable partners. Set unfurling fronds of the common male fern, Dryopteris filix-mas, behind the low-spreading stems of a variegated Cotoneaster horizontalis: uprights and horizontals. Use shuttlecock ferns between clumps of the fat-leaved saxifrage, S cortusifolia rosea: lace and polished leather. Use the Japanese fern, Adiantum pedatum, with anything.

That is another plant I got from my swoop on the Blackthorn Nursery. It stands about 18 inches high, with long, thin, stiff fronds, held almost horizontal and finely fringed. The young growths are a pinkish sort of copper, the colour drifting into pale green as the fronds age. I have it growing in front of rodgersias and new whorls of lily stems. There is not a flower among them, but this little mob stops me more often than anything else in the garden at the moment.

It happened by accident. When I planted the fern, both the lilies and the rodgersia were underground and I had forgotten all about them. I say this to dispel any notion that I lie awake at night worrying about plant combinations. If you choose plants carefully in the first place, they work together more often than not.

Sword-shaped leaves are great allies, separating the rather sleepy rounded clumps that so many herbaceous perennials grow into. On the bank, I use the obliging Iris orientalis. The flowers, white with yellow throats, beardless, do not appear until late June, but the leaves are already more than three feet high, spearing through mounds of thalictrum, giving backbone to a rather spindly rose, supporting a hummock of autumn- flowering sedum.

The leaves act like punctuation marks in a large planting. You don't want too many of them, in the same way as you don't always want to be tripping over commas in a piece of prose, but this iris is a plant that, like the best sort of aunt, can get along in any company.

There is a similar iris from the same Spuria group, called, rather loosely, Iris x monspur, which you can use in the same way. I have not grown it, but have admired it in other gardens, where it makes large clumps, with the same strong, upright leaves as my I orientalis. The types I have seen have blue flowers, of the same fleur-de-lis shape.

Where you want to create the same sort of effect on a smaller scale,

you can use an iris such as I pallida 'Variegata' which holds its leaves

like bearded irises, in flat two-

dimensional fans. They are broad, glaucous and, in this variety, striped with rich cream. The flowers are pale blue. It is growing on a sunny bit of our bank surrounded by the last of the jonquils and the first of the aquilegias, mostly deep-purple kinds.

All these irises sulk when they are moved. They need time to settle. The spuria types are best planted in the autumn, setting the rhizomes only about two inches deep in well-worked soil to which you have added some handfuls of bonemeal. Iris pallida needs more sun than the others and you can plant these in summer, with the top of the rhizome sitting above the ground where it can get baked.

Crocosmia leaves are almost as good as iris, though they do not have quite the stiff, upright formality of the iris's leaves, and they are a greener green, without that glaucous overlay that makes the iris stand out so well. The crocosmia leaves are pleated lengthways. The long ribs are their scaffolding.

They are not as tall at the moment as the iris, but are making useful landmarks between mounds of brunnera. There is far too much of that in our garden, but at this time of the year you forget its later coarseness. With its mounds of blue forget-me-not flowers, it pretends it is an ultra-snob plant. The cream variegated version, flowering now with the early broom, Cytisus x kewensis, is even better.

Blackthorn Nursery, Kilmeston, Alresford, Hampshire, is open Friday and Saturday only (9am- 5pm) until the end of October. Iris pallida is widely available. You can get Iris x monspur from Michael Wickenden at Cally Gardens, Gatehouse of Fleet, Castle Douglas, Scotland. The nursery is open Saturday and Sunday only (10am- 5.30pm) but he does mail order. Iris orientalis is available from The Botanic Nursery, Rookery Nurseries, Cottles Lane, Atworth, near Melksham, Wiltshire. The nursery does mail order and is open Monday- Saturday (10am-5pm).