“There’s nothing quite like it,” say visitors to Chelsea, “the gardens, the glamour, the plants, the sheer quality of everything.” They are right, of course — it’s the envy of the world.

But what’s it all for? What are those gardens supposed to do for us? Certainly they must be attractive, which may mean beautiful or pretty depending on your taste, and it may mean tantalisingly unattainable. They must be inspiring, too, and make you want to rush off and put just that verbascum with just that geum, or fix the tired paving or install a trendy black pond.

But some gardens also teach or tell a story. The great lesson at the moment — and rightly enough — is sustainable, eco-friendly gardening; even the most exotic gardens pays lip-service to it. But does it make for a good show garden? And symbolic, story-telling gardening? It sounds fascinating, but can you see it and feel it on the ground? How many visitors will feel enriched by the idea that “the river of black slate and white marble chips represents the two strands of the human psyche”?

Consider the Cancer Research Discovery Garden MA24, by the designers Jane Hudson and Erik de Maeijer. It is very simple: within an arc of hedging, a spiral of huge granite stepping stones winds inwards through rich, informal herbaceous planting to an open circular space where three granite pouffes (if that’s possible) face a dolmen-like oil-and-light feature.

What does it all mean? Well, “progress”, of course, and in this case the progress of cancer research. But the symbolism is lightly worn. Hudson and de Maeijer know how to do soft, opulent planting. They are also landscape architects who happen to work in garden design and know that less is usually more; so the spiral path is broken into stepping stones to slow its momentum and avoid sucking you in like water down a plughole. It gives you time to enjoy the plants. It’s also only just a spiral — more of a comma, actually — so that once you have reached the centre you do not feel trapped so much as wrapped in the planting.

Carol Smith and Martin Clark Associates have also made a spiral garden WA10. Theirs is an “ancient symbol of energy and time” and represents “going inward” to the “lower heart” of the garden, leaving behind the “tired self” and then “returning outward” to “rebirth”.

The garden features two interlocking spirals, in different materials and separated by a strip of ornamental grass with a dotted line of sculptural balls. At the centre, under a metal palm dripping water, the spirals lock together, their momentum disappearing up the trunk of the palm, around which you can sit and shelter from the dripping fronds. The planting is in geometric blocks. Now all this makes for a striking image, but comfortable and healing it is not. The symbolism has got the better of the design.

Sir Terence Conran’s Peace Garden MA6, for the Imperial War Museum, fares better. It celebrates the 60th anniversary of the end of the Second World War. The garden has two canals, flanked by mixed borders, flowing inwards to a central circular pool. A pyramidal dovecote hovers over one canal. It is genuinely a peaceful garden. The momentum of the water flows quietly to a calm centre where underwater pebbles represent lost lives. The wall is inscribed with the word “peace ” in different languages.

The planting is mostly white, scattered with scarlet poppies, and the trees chosen are all classic symbols — olives for peace, cypresses for mourning, poppies for remembrance and so on. In other words the message is explicit, and its symbols are so widely understood as to require no explanation. If symbolism requires explanation and excuses, it might as well not be there.

Conran’s planting, by the way, claims to be “so varied that it is bound to attract wildlife”. Goodness, I had no idea it was so easy. Designers setting out to teach sustainable gardening, such as Stephen Hall (Wildlife Trusts Lush Garden), might not agree. Hall’s garden, though old-fashioned in design, is charming and full of good ideas for encouraging wildlife. It demonstrates its message immediately, as well as being a garden that you might want to live with.

So does the RSPB/SITA Real Rubbish Garden RS3, designed by Claire Whitehouse and built with recycled materials. It sets out to show that “a garden doesn’t have to be wild to be attractive to wildlife”. True, but does it have to be unattractive to us to be attractive to wildlife? In fact, under an easy-going mixed planting, the garden promises to be quite a strong sequence of crisp, formal spaces, with a generous raised pool and mini-woodland. No wilderness but very liveable, in fact; and the frieze of clear-plastic household rubbish could be most attractive if it is subtly and cleverly done.

Elma Fenton is an Irish landscape architect showing her Moat and Castle Eco-Garden NR40. It has a formal swimming pond — purified by plants, not by chemicals — and virtually all the planting is native. Spoil from the pool is used to make a rolling rural landform, and plants are clipped to make organic shapes. The maintenance style is low-key, showing that you can make a comfortable garden without traditional maintenance and garden centre plants. Fenton’s message, too, is clear at a glance.

What then of Landlab’s Boreal Forest Garden NR38? It highlights the destruction of northern forests, and the design concept “is a forest clearing managed as a garden to harvest non-timber forest products such as pine nuts, sap, blueberries, bark and grasses”. Laudable, no doubt, but this sounds like a health-warning, not a show garden, even though it has a lovely spiral of stepping stones. It belongs under canvas with the educational exhibits and proves it is not enough for a show garden just to parade a message. A designer has to translate the message into an attractive place that someone might wish to live with — a real garden, in fact.

Explore Gardens

• Hampton Court Palace Flower Show

• Chelsea Flower Show

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