Starter's orders: A beginner's kit of plants and bulbs for creating your first garden

When I was young (despite Freud's credo), the thing that I most envied my brother was his Meccano set. The first kit contained most of the basic struts, screws and other components necessary for simple skeleton constructions. Subsequent sets added cogs, axles, wheels and arcs to fill in the gaps and put together more complicated creations.

It is much the same with gardens. When you start, your mind may be full of the fluff of perennials – trendy astrantias, umbellifers, salvias and sedums – but what you actually need is a basic skeleton kit of trees and shrubs to give form and substance to your plot when the perennial stuff disappears. As it will with the first frosts.

I had a great afternoon this week with a friend who, at 36, has finally moved into a house of her own. For years she's been stuffing torn-out pages of gardening mags into a folder, a herbaceous border here, a pot there, a romantic bit of wildflower meadow somewhere else. "At last," she said, spreading this patchwork of stuff over the kitchen table as we started on the delicate work of trying to discover exactly what it was in these various images that had attracted her.

Her notebook was full of plant names, copied out from the captions under her favourite images (a hugely encouraging sign), but it was not long before she realised that the scenes she so loved often worked because of things that didn't appear in her notebook at all. The border sang out because of the dark green backdrop of the hedge behind it. The meadow needed the apple trees rearing up from it and spreading their mossy arms over it. The herbaceous borders she most liked worked because there were strong anchors of shrubby stuff in it, usefully solid bulwarks between wispy flower stems, good buffers between colours that otherwise might quarrel.

All this was excellent. Lessons that you learn yourself always stick more clearly than ones that have been banged into you by someone else. And even without this session, Alice would eventually have worked out the tree/shrub thing for herself. But I was glad she'd been saved from the disappointment of wondering why all the herbaceous stuff she'd planted from her notebook wasn't singing as it was in the original pictures.

One simple solution is to turn to box and yew and let them provide winter form and structure. There's a good reason why these two evergreens provide vital underpinning in so many gardens: they aren't fussy about soil, sun or shade and they need very little maintenance apart from their once-yearly, late summer haircuts. Both can be clipped into living sculptures – domes, pillars, globes, pyramids – to provide contrast in a sea of perennials. It's a look the glamorous Norah Lindsay favoured in the 1920s and which designer Tom Stuart-Smith has made famous more recently.

But as a new gardener (and in a smallish space) it's not easy to restrain yourself to box and yew, however elegant the results. Some kind of tree is a must and with a little thought, the starter kit of shrubs can be organised so that something is flowering every month of the year. From April to June, you'll be spoilt for choice. From October to March, you'll have less from which to choose, but even in the dreariest months of the year, Alice need not be without something to sniff at and admire: magnificent mahonia in November, viburnum in December, hamamelis in January, daphne in February, osmanthus in March. Several of those are evergreen. All are scented.

As space is limited in Alice's garden and she has the needs of two small boys (aged four and two) to think about, we spent a lot of time discussing trees. It'll be the biggest piece of furniture she puts in her outdoor room. It's the single most important decision she has to take. Weeping willows and blue Atlantic cedars both look dangerously seductive as babies, but (even if only for the sake of novice gardeners) should have huge red danger labels tied round their necks. Willows grow enormous, not only up but out and being great lovers of moisture, will suck the ground dry. The Atlantic cedar has the potential to make an even bigger tree, becoming a terrifying cuckoo in the nest of the average town garden.

In a small garden, it seems a shame to waste the opportunity of blossom, so from the list recommended by Kevin Croucher, who has a magnificent tree nursery in Devon, I'd choose from Amelanchier lamarckii, the fine thorn Crataegus persimilis 'Prunifolia', a crab apple, a cherry (it would have to be a smallish one and Croucher suggests either white 'Shogetsu' or pink 'Spire') or a rowan, probably Sorbus commixta 'Embley'.

Several of these pay rent three times over, providing fruit and fiery autumn leaves as well as their spring blossom. I'm mad about thorns, but they can be slowish. If I were Alice, I'd probably choose a crab apple. They are all good-natured, obliging little trees that, even at 10 years old, are unlikely to be more than 20ft tall and half as much wide. What you need to decide is whether you prefer pale or dark blossom and whether the fruit should be reddish or yellowish.

After that, it becomes a game of mix and match. If you like pure white flowers and large red fruit, then get Malus x atrosanguinea 'Gorgeous'. If pale pink blossom and yellow fruit, then Malus 'Gardeners' Gold'. Croucher recommends the Japanese species Malus toringo, a small, slightly pendulous tree with white blossom and yellow fruit, and Malus transitoria 'Thornhayes Tansy', slightly bigger, with masses of white blossom and amber-coloured fruits. I can vouch for Malus hupehensis, which I planted four years ago: white flowers, glossy little red crab apples, but potentially a much bigger tree than either of the other two.

Whatever she chooses, Alice will have more planting room underneath if she gradually snips her way up the trunk of her new tree, taking off a couple of the baby branches each winter. This must be done gradually, first cutting the side shoots back to "snags" of two or three buds, before getting rid of them altogether the following year. When there is about five feet of trunk, clear of any growth, she can stop. Alice hasn't yet decided on The Tree, but I was glad to see some of the names of some good trees and shrubs joining the perennials in her notebook.

Thornhayes Nursery is at St Andrews Wood, Dulford Cullompton, Devon EX15 2DF, 01884 266746, thornhayes-nursery.co.uk. The nursery is open Mon-Fri (8am-4pm) and Sat (9.30am-2pm)