Suppliers of wildflower turf should do well after this year’s RHS Hampton Court Show. Meadow grasses dotted with wildflowers such as campion, knapweed, oxeye daisies and poppies feature in many of the gardens, both large and small, as habitats for butterflies and insects or simply to celebrate the beauty of natural meadows. But many designers had been forced to add some last-minute plug plants to create extra splashes of colour.

“I bought rolls of meadow turf and grew it at home, on a plastic membrane, for several months,” said the designer Francesca Cleary, who used a strip of meadow to contrast with the cool whites and greens of her “Magic Garden” winter woodland scene. “It looked beautiful in May and early June,” she said, “but was beginning to go a couple of weeks ago. And then the rain and wind of the past couple of weeks hit it, so I added some achilleas, coreopsis, catanache and oxeye daisies to give it a bit of a lift.”

The surprise plant of the show, though, is lettuce. Predictably, it features in the many Grow Your Own gardens and displays (including Best in Show “Dorset Cereals Edible Playground”) but it is also used for texture and colour — in various shades of green, bronze and burgundy — in many of the ornamental gardens. In the Conceptual Garden “Ecstasy in a Black Box”, densely planted seedlings of “Salad Bowl” create a rolling sward of vivid green, which the designer Tony Smith uses to suggest the “euphoria” aspect of his design, a perspective on bipolar disorder. “I chose this variety because when they first germinate they’re a dull green but after 14 days the true leaves appear and you get this fabulous vivid green,” he said.

The decorative effect of various different varieties can also be seen in the Growing Tastes Marquee and in the adjoining Kitchen Garden, a cornucopia of vegetables presented by Wisley Gardens for us to try in our own gardens.

The Oriental section includes easy-to-grow pak-choi, two spinaches (Chinese and Ceylon) and a giant metal wok mounded with the purple flowered chilli “Filius Blue”. In the Floral Marquee the decorative potential of many more varieties of chilli, including “Chill Out” with deep purple leaves and “Cookoo Box Cheeky” with tear-drop lemon yellow fruits, are displayed by Cookoo Box, while Pennard Plants (in the Growing Tastes Marquee) has a stand of Mexican tree spinach, an annual with lipstick-pink leaves that grow up to 5ft.

Thyme feature in many of the small gardens, planted in ribbons, mounds and punctuating gravel in Mediterranean-style designs. These designers are responding to one of the key messages in the Climate Change Dome — that summers in Britain are becoming drier and hotter. Thyme would cope well with these conditions, and Jekka McVicar’s display in the Floral Marquee shows that you can make a stunning design with the hundreds of varieties of thyme, ranging from the compact prostrate Thymus serpyllum “Minimalist” with pinprick purple flowers, which McVicar recommends for walking on, to the looser and taller T. pulegioides with open pink flowers.

Looking at the worst-case predictions — the Met Office contrasts today’s top summer temperatures of 31C on the South Coast with a possible 43C in 2080 if global warming continues at its present pace — the designer Fernando Gonzalez presents cacti (especially the weird, organically shaped variants) and the spiny-trunked houseplant Pachypodium lameri, in his small, spare garden (“Pulsations”), as our garden plants of the future. On the Plant Lovers nursery display in the Floral Marquee, opuntias and other familiar succulents such as echeverias, are offered in shades of grey-green tinged with pink and bronze.

The Back to the Future garden, which shows sustainable and organic growing methods used in arid regions of Africa, presents water- saving ideas including bag gardens — fill a hessian sack with a central column of stones, pack round with compost (two parts soil, one part garden compost), cut holes in the side and plant up. But if you are prepared to keep watering, two star performers for hanging baskets are the purple Verbena “Seabrook’s Lavender” and salmon-pink Begonia Million Kisses ‘Romance’ which make walls of colour in the Floral Marquee.

The RHS Hampton Court Show continues until July 13; www.rhs.org.uk