A week before the opening of the UK’s most prestigious flower show, the site is full of JCBs and people in hi-vis vests with steel-capped boots. Some gardens still look like construction sites, including part of the RHS Cop26 Garden – except that this one is finished.

Drainpipes, a manhole chamber, old concrete and industrial offcuts lie strewn around. “When I told people we were taking this stuff to Chelsea they thought we were fly-tipping,” says Marie-Louise Agius from landscaping company Balston Agius, who designed the garden. It has taken 12 people three weeks to put together.

Among the mess is a heavily manicured, fine ornamental lawn and paved-over area. “It goes against what we want to be encouraging people to do,” says Agius. “From an environmental perspective, you really shouldn’t be wasting water on watering lawns.”

It’s an unconventional addition to the 108-year-old Chelsea Flower Show, but this thought-provoking creation is a warning of how dead our planet will be if we don’t change the way we manage green spaces, including over irrigating and using excessive drainage and too many chemicals. Agius says: “It’s a representation of the status quo – which isn’t good enough, as we’ve seen all through the summer with the floods and everything else that people have been experiencing.”

The “decline” section is only a quarter of the 20 by 20 metre Cop26 garden. The other sections look at “adaptation”, “mitigation” and “balance”, and how gardeners can be part of the solution. It has been funded by the RHS with the aim of highlighting the importance of sustainable horticulture ahead of the Cop26 climate summit to be held in Glasgow in November.

Separating decline and adaptation is a burnt hedge, symbolic of the planet’s increasingly destructive wildfires. Agius says that with temperatures on track to rise by 2-4C this century, gardens could become more Mediterranean, filled with fleshy, leathery and furry plants sitting on raised beds. These varieties are better at surviving more extreme droughts, downpours and heatwaves.

Agius wants people to come and see which plants may be more climate-resilient, and incorporate them into traditional gardens. Included in the display are yuka, furcraea and agave americana.

“People won’t emote to this in the same way that they will to a typical cottage garden,” she says. “It’s about a balance, and taking some of the plants here, and making the most of their properties.”

The next part of the garden – mitigation – takes visitors back to a typically bucolic English scene with an exuberant wildflower meadow, little pond, and beehives. A small ditch provides places for water to settle and damp-loving plants to thrive. The soils are well aerated with worms, increasing the amount of water the ground can absorb, which can help to reduce flooding downstream. Pollinator-friendly plants and a couple of wood piles keep insects happy.

The final section of the garden is balance, which incorporates vegetables, as well as long grasses and fruit trees including lime, quince and pomegranate.

“Something to look at is growing your own vegetables and thinking about food miles and encouraging people – where possible – to enjoy growing their own produce,” says Agius.

According to government data, there are 730,000 hectares (1.8m acres) of private garden in the UK – nearly twice the size of Somerset. And in cities, nearly 30% of domestic space is taken up by gardens. Eating less meat, flying less and creating wildlife-friendly green spaces are all ways people are being encouraged do their bit to tackle the climate and biodiversity crises.

Prof Alistair Griffiths, director of science and collections at the RHS, hopes the government will recognise and appreciate how important gardening is for climate resilience ahead of Cop26. He says: “We’re a passionate nation of gardeners. Gardening is one of a number of ways the UK general public can take action to help to mitigate against climate change.”

Reflecting a growing interest in gardening under the Covid-19 lockdowns, the latest categories to be added to RHS Chelsea are balcony gardens and container gardens, which have become more popular as people have focused on getting the most out of where they live.

These pocket gardens fit in a 2 by 5 metre area and show how much can be done in a small space using pots. They are made by gardeners coming to Chelsea for the first time.

Nicola Hale, a landscape designer at Landform Consultants who created the Landform balcony garden, suggests that people wanting to get into smaller urban gardens start first with just a few pots. She says: “Test yourself, and see how well you can take care of them, because sometimes people plant things and forget about them.”

Balcony gardens also act as pollinator corridors. Hale looked into what plants attract solitary bees, bumblebees, honeybees and hoverflies. She says: “It came up that they were most attracted to purple and yellow flowers, so that’s why we chose this palette.”

One of the plants included in the Landform balcony garden is Salvia, which releases a minty smell when shaken. Like many flowers in this garden, including sunflowers and catmint, it is adapted to dry conditions, so won’t die if it doesn’t get watered while you go on holiday. Other fragrant plants, such as jasmine flower and rosemary, have also been included.

“If you’re working from home … spending eight or 12 hours a day working, it’s nice to put your laptop away, then go out into the air, see some green, see some birds and insects, and take that break,” says Hale.

The number of gardeners in the UK has grown by nearly 3 million over lockdown and now stands at 30 million. Organisers hope the pocket gardens will encourage increasing numbers of younger people on lower budgets to get into gardening.

The team at Landform has been busy over lockdown with people wanting to create gardens in all kinds of spaces. “We were working much longer hours,” says Catherine MacDonald, the firm’s principal landscape designer. “We had so many inquiries from people in different-sized spaces who were just so much more enthusiastic about their gardens. I guess they weren’t spending money on holidays so they’d spent money on their own spaces, and perhaps learned to appreciate them more.”

The Chelsea flower show was cancelled last year and this year was postponed to 21-26 September from late May because of the pandemic. The Cop26 garden will go on to be incorporated into the RHS Garden Bridgewater in Greater Manchester and will be used to teach people about the climate crisis and gardening.

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