In the Eighties, when designers controlled everything visual, style gurus laid down intricate rules about how our immediate surroundings should look - urns yes, gnomes no. Censorious about our houses, gardens and clothes, they left very little to the imagination. Now, it is all right to do whatever takes your fancy, slowly and on your own, without a designer breathing down your neck.
A private garden is a particularly good place to indulge in idiosyncratic preferences and the belief that there is no such thing as absolute taste. Here, beauty can be in the eye of the beholder, because unity is what matters. As long as the consistent vision of the owner governs the choice, it will be beautiful - maybe only to one person, but gardens are essentially personal spaces where what you like is what counts. They can be the owner's outdoor art gallery. You can choose items from a variety of sources that cost almost nothing, so that when you become bored with one effect you can always try another somewhere else.
Abandoned objects are one of the best forms of artless art, because they are in the tradition of the 18th-century garden ornament, which was meant to prompt reflection and suggest associations. Classical statues suggesting heroism, or urns that hint at mortality, have lost their power to move us. The ideas we attach to visual objects are perhaps better stirred by everyday things that have ceased to have a useful life. An old wheelbarrow or garden roller, or a watering can that is too heavy to use, are modest examples of things that suggest the passing of time. They also give human scale to a garden, suggesting that the person who was using them has disappeared for a moment, but will be back again soon.
Not every garden will have room for a bottomless boat, but the photograph opposite shows how potent an image it provides. Here, between the curved sides of oak, children might play for hours, while the onlooker dreams of summer on the river or the sadness of things that have seen better days. The trick of stimulating the imagination with an object can be used in many ways. A broken bicycle might not be everyone's idea of a garden ornament, but for some it could carry intimations of mortality better than any abandoned wheelbarrow. For although a garden seems to be a place where time stands still, the passing of the seasons and the constant decay in nature underline a greater scale than the wristwatch or the clock. Any abandoned object is only reinforcing that universal theme.
Outside a Palladian villa in Vicenza, Italy this year, the visitors had stuck their umbrellas into the box hedges on either side of the grand entrance, which made me laugh and think about how times have changed. If you can put an object in the garden which raises a smile (without damaging the hedges), you are adding to the immense pleasure of being out of doors: if you must have a statue, put a hat on it. If you like statues of animals, set them in unlikely spots: a cat is more fun up a tree than on the patio. A bird can sit on the windowsill and even mass-produced concrete images rate a second glance if placed in odd settings.
For those who find jokey surprises or thoughts of life and death unacceptable in the garden, there are more reassuring ideas. Order and honest toil can be suggested by a tidy toolshed. A collection of unplanted clay pots stacked in orderly rows also has the peculiar charm of a good tool in the right place. Logs piled up for winter mean warm fires indoors. A rotary washing line may not be a pleasure to the eye, but a line of clean clothes billowing between apple trees is quite another matter.
Found objects are another source of pleasure. The irresistible stone discovered on a beach can be brought home to join a collection of shells and stones from other holidays. Set out on a wall or a flat stone table, they act as a reminder of the places where they were found, or of the people who shared a summer. The animal bones, fossils, fir cones and lumps of rock that are the inspiration of modern sculptors such as Peter Randall Page can be a private source of wonder that costs nothing. Nature's cast-offs, not magnificent enough to stand alone, can be arranged in patterns, as they formerly were in grottoes or in the homes of those late 18th-century spinsters who spent their days setting out ferns, feathers or molluscs. Found things, as our ancestors knew, are not difficult to display. It is, after all, a little like the grouping of flowers that you try to turn into a picture. But with inanimate objects the task is easier.
Creating your own ornaments is another option. For hobby artists, the garden offers a permanent exhibition for works that may be too large to take indoors. Pottery, mosaics, even trompe- l'oeil pictures all have a place outside. Amateur potters will enjoy seeing their handiwork against a background of green. They may not be perfect but, like the things that children bring home from school, they will have an aura of belonging that excuses imperfections.
Making patterns with stone, pieces of glass, or broken china set in mortar, is another way of expressing your personality out of doors. Most of these skills are not difficult to master, especially if you stick to a pattern which you have drawn up on graph paper beforehand.
For that garden seat where paving seems a good idea, a message in pebbles might be more fun. If you can paint, an easy option is to add a view to a dull fence, or create a fake window, complete with curtaining and geranium in a pot, on the side of a garden shed. Abstract artists might think of more ambitious schemes. And for those who cannot compose a picture but like colour, the children's climbing frame might be a cynosure, painted in barley sugar stripes. Even those who despise gnomes might find a space for pottery ones made by their own children and painted with affection. In the 19th century, gnomes appeared in the rockeries of grand English gardens; it was only when they became too popular that disapproval set in.
Scarecrows are more ephemeral creatures: their clothes will not stand up to years of exposure. Sensitive gardeners who prefer not to be faced with a memento mori may not like the idea of finding these models of a vagrant among their vegetables. But it is worth remembering that if you are trying to provoke an emotional response, then shock may be more suitable than sentimentality.
Many gardeners will shun these suggestions, but those for whom a garden is a place to sit and think, rather than somewhere to look at the flowers, may find the germ of an idea. Subjective rather than objective gardening is much easier if you use objects to create your own atmosphere. And if they cost almost nothing, what do you have to lose? Abandoned, found or created, they can all be thrown away - and then you can start again.-
The photographs accompanying this article are taken from Decorate Your Garden by Mary Keen, published by Conran Octopus, price pounds 17.99