Dame Judi officially opened the Queen's Canopy Garden, ITV News Royal Editor Chris Ship reports
The James Bond actress was one of several famous faces who attended the opening ceremony and got a first glimpse of the first ever autumn Royal Horticultural Society (RHS) Show.
This year's show will take on a more climate conscious approach ahead of the COP26 conference, while dahlias, pumpkins and autumn colours replaced spring and early summer blooms, as the show shifts seasons due to the pandemic.
Dame Judi said the show looked “as always, immaculate” as she officially opened the RHS Queen’s Green Canopy Garden - the largest plot at the show - featuring 21 trees and more than 3,500 plants to highlight the importance of trees and woodland.
The Academy Award winning actress said she had two passions in life, William Shakespeare and trees, and had planted trees in her garden to pay tribute to each of her friends who had died.
Dame Judi said she had already got her tree to plant in honour of the Queen’s platinum jubilee - a Himalayan silver birch.
She said: “We have never had the opportunity to celebrate a platinum jubilee before, never had someone 70 years on the throne before.
“The work the Queen has done, is doing, is remarkable, and what better way to celebrate than by having a garden and then for all of us to take that on and plant a tree, which is also doing something for climate change.”
Celebrities including Anneka Rice, Downton Abbey actor Jim Carter, The Only Way Is Essex's Gemma Collins, and actress and comedian Sally Phillips were among those getting a first look at the event before members of the royal family, including the Earl and Countess of Wessex and the Princess Royal, tour the show later on Monday.
Meanwhile, Environment Secretary George Eustice and other ministers toured the Cop26 garden - one of the highlights of the show focusing on the climate crisis in the run-up to key UN talks being held in Glasgow in November.
The garden is divided into four sections exploring different aspects of climate change, including negative garden practices such as paving over areas, ways to cope with temperature changes such as planting for drought, measures to support the environment and working with nature.
Its co-designer Marie-Louise Agius said she hoped the garden, which features composting, a wildlife garden, leaving edges of lawns long for nature and ways to manage water better, would be informative, educational and inspirational.
As to what visitors, or viewers seeing it on TV, could take away from the garden, she said: “I hope it will empower them.
"So many of these enormous issues we face – and climate change is a global issue – everyone assumes it’s for other people to deal with, it’s for governments to deal with.
“Yes, it is for others, yes, it is for governments, but it’s also for each one of us individually. What I want people to take away is to think: ‘I can make a difference.'”
Shifting the show to autumn this year - after it was cancelled altogether and taken online in 2020 as a result of Covid-19 - has provided challenges for designers who have had to change their displays.
Different plants have taken centre stage compared to what is seen at the show’s usual May slot, with blooms such as asters and dahlias, trees full of fruit and berries, grasses and seed heads, and autumn bulbs such as nerines.
The grand pavilion is missing its usual floral scent, as pumpkins and other harvest fruit and veg take centre stage.
Helena Pettit, director of gardens and shows at the RHS, said putting on a September show had been a "challenge", adding: “But one that’s been embraced by industry, and from that perspective it’s just been fantastic.”
Other gardens at the show include the M&G garden designed as an urban green haven for people and wildlife in the form of a “pocket park”, a Guide Dogs 90th anniversary garden and a series of balcony gardens for those with only a little outside space to spare.
The Florence Nightingale Garden, which marks the bicentenary of the birth of the trailblazing nurse and celebrates the importance of the nursing profession in the 21st century, will be relocated to St Thomas’ Hospital in London in 2022 – to a spot currently being used as a Covid-19 testing and vaccination centre.