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Gardening: Spring team

This time of year brings gardeners out in a plant-buying rash, says Anna Pavord. But just as important as spring blooms are plants that will keep your garden going all summer long

Every spring, gardeners have the beguiling sensation of making a fresh start. Blinded by optimism of the most irrational kind, we start acquiring plants rather faster than plans as to what we are going to do with them. Ceanothus, chaenomeles, anemone, spurge, each becomes the centre of a new dream. The danger of this spring euphoria is that we end up with a garden crammed with plants that are at their best in April and May but have nothing to show for the rest of the year.

All gardens need an underpinning of structural plants, things that are the equivalent of the most important pieces of furniture in a room. Some of them should be evergreen, so that in winter, the garden does not entirely dissolve into a mess of rotting leaves and skeletal branches. These structural plants will hold the whole garden together between the seasons, while the tulips come and go, the roses bloom and the dahlias build up to their late summer peak.

In choosing these landmark plants, we should be looking for things that provide a long season of interest, that are architectural in form, or that have leaves as good as their flowers. Euphorbia characias subsp. wulfenii is an outstanding example of a plant that has presence the whole year round, not just when it is flowering. If you've got space for it, shrubby Euphorbia mellifera is equally good. So is the variegated dogwood, Cornus alba 'Elegantissima'. Through winter and early spring it's a spacy construct of bright red stems, upright when young, arching as they age. Then it leafs up and becomes an elegant beacon, the stems clothed in softly variegated leaves. I'm not generally a fan of variegated plants – they are often too fussy – but the dogwood manages the stunt beautifully.

With these big pieces of furniture in place, you can start filling up the gaps in between. It helps to think of planting as a three-tier affair. Three separate groups of plants can occupy the same piece of ground, though not all will necessarily come to a peak at the same time. High up you have trees and large shrubs, in the middle tier the herbaceous perennials, and scrabbling around underneath, low-growing ground-cover plants and bulbs. By using the space carefully, you can ensure, for instance, that a spring flowering tree has summer-flowering perennials under it, interspersed with bulbs, perhaps colchicums, that come spearing through the ground in autumn. That patch of ground will be earning its keep over a long season in the garden.

In the kind of garden most of us have, we will need more plants to fill the middle and bottom layers than the top. And in my own garden, I feel that the second half of summer is never as good as the first. So I'm trying to make one border sing particularly well from July to September; even if the rest of the garden is quiet then, I'll have one bit that is at its peak. The backdrop is made up of Irish yews, still young but already making good, strong evergreen pillars. Within the bed, the landmark plants, the permanent pieces of furniture, are spurges, the shrubby Euphorbia stygiana from the Azores – fabulous sea green foliage and lime-green flowers in May and June – and the smaller Euphorbia characias 'Portuguese Velvet' with equally good evergreen foliage. Both would be worth growing for their leaves alone.

Because one of the few rules in gardening is that you can never have too many spurges, I've also added Euphorbia palustris which comes into bloom slightly later than the others (June-July). The flowers, though an extraordinary, wild lime-green, tone well with any colour you put with them. They are elegant with white, cool with blue, stunning with pink, sophisticated with yellow. Structure is important too; the plants hold themselves well and have excellent foliage, so it's not surprising that spurges should be among your best friends when you are planning planting schemes.

There are a few grasses in the bed too, though less than I started with. Calamagrostis x acutiflora 'Karl Foerster' was a noisy disaster last summer, the flowering stems collapsing all over their neighbours before even July had finished, so I'm going to try Stipa brachytricha in its place. It's tall – 140-150cm – but I like that and perhaps it'll be able to hold itself with more grace than the much-hyped calamagrostis. I hope so, because I want it to partner the old rudbeckia 'Goldsturm' that in a good season produces its yellow daisy flowers all the way through from August to October.

Inula will do that too, though it's even taller than the rudbeckia and may turn out to be too coarse an ingredient for this particular mix. Verbascums would be safer, though the flowers start earlier and have usually shot their bolt by August. Many have yellow flowers, but Verbascum phoeniceum 'Rosetta' has spires of carmine pink flowers; 'Violetta' is slightly taller with spikes of purplish-violet. Sunflowers are another option. I tried to do them last summer in that border, but after I'd planted out more than 20 lusty young plants, lovingly raised from seed, the whole lot were eaten by slugs. Or snails. I didn't see them at it. If I had, it wouldn't have happened.

For the lowest level of planting, you can scarcely do better than herbaceous geraniums, especially if you choose the newish blue one called 'Brookside' which has an astonishingly long flowering season. 'Rozeanne' is good too, though the habit is different. It doesn't make big clumps like 'Brookside' but wanders about, like the older variety 'Buxton's Blue', throwing arms of blue flower into anything around it, friendly but not overbearing. Salvias (even the native meadow clary, S. pratensis) have never been quite as reliable or as long-lasting in our garden, but I'm thinking of having another go with the one called 'Indigo'. The flowers are carried in whorls up the lax stems, lippy, like all salvia flowers and a violet kind of blue. If the rabbits are kind and the rain not too infrequent, this collection of plants should see us through the down-time of August very nicely.