Learn your lines and avoid the muddle: Less can be more when it comes to planting, writes Anna Pavord. Now is the time to think about form, structure and back-to-school discipline

AFTER 17 years of schooling in various forms, it is difficult to shake off the notion that the year starts in autumn. New uniforms, new pencils, new teachers give way to new television schedules, new (or revamped) newspapers, new novels.

The notion of a fresh start spills over into gardens, too. By this stage in the year, gardeners have a vivid inventory of their mistakes and of things that did not go according to plan. School report phrases consequently echo in the ear: 'a certain lack of direction', 'over-exuberant', 'needs a firm hand' and the inevitable 'could do better'.

I always hated that last one. Just once, I got 93 per cent in an end-of-term geometry exam, but the maths mistress, conditioned, I suppose, by the sight of my name, once again put 'could do better' on my report. Even my parents, who usually ranged themselves firmly with teachers, school and all other forms of authority, thought that was slightly odd.

Taking stock of the garden as a whole is more important at this stage than racing out to buy new shrubs and trees to replace the duds. There are two separate areas to think about here: the structure and the planting. One is cheaper to sort out than the other.

Form of one sort or another is vital and if it is lacking in terms of the overall garden structure, and there is no money to spare for new paths or screens or hedges, you can reinforce it by patterning the planting.

This does not mean restricting the planting to a formula - one of this, two of those and then one of this again - but it does often mean using more of less. In a small garden, this requires superhuman restraint, for the urge to cram in as many different plants as possible is strong.

But a mix can quickly become a muddle and the benefits of introducing some patterning in planting schemes should outweigh the disappointment of turning your back on a 'gotta have' poppy or the latest in a long line of hostas.

Reinforcing the lines of paths can have a marked effect on the overall look of a garden. Those that are straight and wide and paved will probably not need this help, but the lines of narrower, curving paths easily become swamped.

Think of edging the path with the same plant for the whole of its length. This immediately makes the path more important. The edging also has a unifying effect on the planting behind it; it all begins to look less random.

Of course, you need the right plant for the job. If you plant something that is going to flop all over the path (as I did with alchemilla) or something that grows so tall that it obscures the plants behind, you will be adding to, rather than solving, your problems.

You need a plant that can bear close inspection for as long as possible. This usually means something with leaves at least as good as its flowers. Alchemilla is pretty good in this respect, although it gives you nothing through the winter and self-seeds if you do not leap promptly enough on the dying flower heads. You can get over the winter gap by planting masses of dwarf crocus in between.

Its overall greenness is much in its favour. If the edging is of a strong colour such as purple or yellow, it may get in the way of your planting schemes behind.

London pride is even better than alchemilla, better behaved and not programmed to dive underground at the first frost. Its rosettes are soothing and the froth of pale flowers in May is a bonus. It will grow in the deepest shade, is easy to transplant and quite quickly swells to fill whatever space it is allowed. Flopping is not in its nature.

And then there is erigeron (Spanish daisy), which I have used between paving stones, but which would make an equally good edging. It is still going flat out, having started in spring with white daisy flowers on low plants. It lacks the leafy bulk of alchemilla or London pride, but in a cottage-style garden would be a good alternative for edging paths.

Using the same plant more than once, particularly along the front of a border, also helps to give cohesion to a design. I have decided this is the answer for a dark, north-facing bed of thick, damp clay that has some big-leaved hydrangeas such as H. sargentiana and H. quercifolia in it.

The bit of this border I think works best has a variegated Cotoneaster horizontalis in front of H. villosa with ginger mint, ferns and a dark-leaved saxifrage, S. fortunei rubrifolia, fiddling around the edges.

The cotoneaster is the plant that I think would be worth repeating further along the border in front of the decaisnea that is now bearing its extraordinary crop of soft sausage seed pods. They are navy blue, a weird colour in the garden.

There is a gap there anyway that needs filling and repeating the cotoneaster will, I feel, be better than introducing a new plant. It is good enough, too, to stand duplication. I would not feel the same way about buddleia or berberis, but the cotoneaster holds itself well, in a stiff, rather stylish way and the variegation lights up what otherwise might be quite a heavy look. Each tiny leaf is edged with cream.

When you are casting about in your mind for suitable candidates to use in these situations, plants that you would welcome seeing more than once, those with strong foliage win nearly every time. This is partly because they have a long season of interest. It is also because, in planning plant groups, you tend to forget that foils are as important as features. The one sets off the other.

This is why I am drafting in several plants of the dark-green Helleborus foetidus to rescue a cream, yellow and green planting in the shade of a beech tree. The spot is not propitious, but it can be fed and, fortunately, the hellebore is tolerant of poor growing conditions.

The problem was not the position but the fact that there were too many variegated and pale plants there and not enough to set them off. The patch is also very weak through the winter. The hellebore, I hope, will solve both problems.

Another way to pull together a shapeless garden is to give it a strong set of landmarks. The opulent option was to use urns and pillars, obelisks and follies. As you walked around the garden, each of these fixed points provided a focus for what was round it.

You can adapt the same notion, using plants in place of obelisks (though obelisks are not to be sneezed at; stone provides a very good foil for greenery).

A landmark plant needs to be the opposite of a plant that you might use for edging. It must be a one-off, strongly architectural, an extrovert, a shark among minnows. Once again, leaves and habit of growth seem more important here than flowers. Aralia is a classic landmark plant, more particularly the white variegated version, which is now carrying enormous flat, creamy flowerheads, two feet across. Think of a head of elder blossom, blow it up, add a pinkish tinge to the stems and you will get the general idea.

But the flowers are not what puts it in the landmark class. It is the leaves, which can be up to 4ft long, arranged as a series of leaflets, paired along mid-ribs that branch out from the main central rib of the leaf. The aralia concentrates so hard on its leaves that it forgets to do anything about branches or twigs. The leaves spring straight from the chunky main stems, so in winter, after they have dropped, you are left with the most skeletal of landmarks.

'Spare,' said a student from the Architectural Association who stayed with us for a while this year. In his eyes, there was no greater praise. He went on to write a thesis about the destructive properties of plants in a constructed environment. I know only too well where his examples came from.