In the run-up to the RHS Chelsea Flower Show there is always much excitement about the emerging themes. This year the advance bulletins have been about sustainability, bees, the cosmos and art in the garden. But there is a frustrating silence about the show gardens’ signature plants.

The designers often have to make last-minute substitutions, because of plants peaking too early or late, or failing in some other way. Being prepared to change direction is all part of being a Chelsea designer.

“If you’re doing a garden,” says Michael Balston, the chairman of this year’s judging panel, “you should have plenty of plants up your sleeve in case of any eventuality.”

It’s not until we walk up Main Avenue from the Rock Garden Bank (this year the location for the Floral Design Marquee rather than show gardens) on the opening day that we discover which are the Zeitgeist plants and colour palettes.

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It is uncanny how many of the 20 designers have predominantly used irises, salvias, astrantias, libertias, foxgloves and alliums in shades of white, purple, burgundy and soft yellow, combining them with golden and bronze grasses such as stipas and carex.

It could be that the unusually dry and hot early spring put paid to using many umbellifers, aquilegias, geraniums, euphorbias, tulips and peonies, or it could be the Tom Stuart-Smith effect – the inspiration provided by his 2006 Best Show Garden.

“Designers look at previous gardens and see which plants work,” says Mark Fane, of Crocus, which supplied four gardens. “Take Salvia ‘Mainacht’ for example. It’s a wonderful intense purple, is long lasting and doesn’t flop. Ideal for a show garden. Alliums too – they’re totally dependable for this time of year, and add strong accents to a planting plan.” It doesn’t mean the gardens look the same, though. In Jinny Blom’s garden for Laurent Perrier, the burgundy-leaved Anthriscus sylvestris ‘Raven-swing’ and arching Stipa gigantea weave a veil above the swathes of Astrantia ‘Roma’ and Iris sibirica. In Andy Sturgeon’s Cancer Research garden the grasses and perennials spill out from under the outstretched arms of a glade of Cornus controversa and the palette is enriched with roses such as blackcurranty ‘Cardinal de Richelieu’ and near-purple ‘Rhapsody in Blue’.

Some gardens offer strikingly different planting: Sarah Eberle’s boldly conceived Mars landscape for Bradstone, which took the prize for best show garden and won an RHS gold medal, introduces knobbly succulents such as Cereus monstruosus and pincushion cacti among more familiar fig trees, agaves and opuntias, while Laurie Chetwood’s Urban Oasis is centred on a 12m (40ft) high kinetic “flower”, which works both as a sculptural installation and generator that pumps water and provide power for lighting, and emerges from a cluster of clipped yew spheres.

For sheer richness of planting, a prize must go to Ulf Nordfjell’s A Tribute to Linnaeus and Kate Frey’s Fetzer Sustainable Winery Garden. It took three of Nordfjell’s team 12 hours to plant up the small but stunningly effective rippling patch of groundcover, using scores of tightly packed Asarum europaeum plants. Kate Frey and her team spent eight days studding the vinery hillside and wetland area with about 6,000 individual, vibrantly coloured wildflower plants.

The best show gardens are just that: spectacles that should excite all your senses. You don’t expect to be able to recreate them in their entirety in your own patch – though you will certainly steal ideas and details.

The small gardens – courtyard, city, roof and chic – play that role, and although there are one or two minimalist offerings, such as Alan Gardner’s lawn wave and Perspex panel creation, many of this year’s designs are eminently reproducible. Adam Frost’s Realistic Retreat has everything a small contemporary garden can deliver: elegant planting of grasses and perennials offering scent and movement, a simple water chute and an arresting stone sculpture.

Meanwhile, in the Grand Pavilion, Freya Lawson’s The Rhus Garden, with its woven oak fencing and bold red planters with complementary evergreen planting, will have many visitors rethinking their roof spaces.

The Grand Pavilion is also the place to see the full range of traditional planting and new species and to pick up tips. The students at Writtle College have devised a three-storey wildlife hotel made from clay tiles, old wood, brush, hollow stems and pebbles and planted up a little nectary garden, small enough to fit in the tiniest back yard, to encourage insects to take up residence. There’s a bee-friendly garden on the British Beekeepers’ Association stand, where urban gardeners are encouraged to set up their own hive. The reward is the honey, but also the knowledge that they will be helping to stem the decline of one of nature’s most crucial pollinators.

The Fortnum & Mason show garden, with its elegant copper-roofed hives, was not allowed to bring its own bees but, thanks to nectar-rich flowers in many of the gardens, bees found their way there anyway. Even on the overcast opening day there they were, zipping across Main Avenue from Kate Frey’s compositae to Jinny Blom’s umbellifers and then on down for a top-up at Sturgeon’s and Nordfjell’s nectar bars.

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