Chelsea Flower Show: Queen is joined by family for tour
The Queen was joined by the Duke of Edinburgh, the Prince of Wales and Prince Harry for her visit to this year's Chelsea Flower Show.
The monarch congratulated her grandson on his work for an African charity as she toured a garden designed for it.
Prince Harry, who has just returned from New Zealand, said parts of the garden were "exactly like Africa".
Horticulturists from around the world are displaying their designs at the Royal Hospital in Chelsea.
The launch of the show, which opens to the public on Tuesday, comes as its organisers say nearly a quarter of the UK's front gardens are now paved over.
The Royal Horticultural Society (RHS) is urging householders to buck the trend by growing more plants.
At the show
By Victoria King, BBC News
From giant jammy dodgers to death and astrophysics - the Chelsea Flower Show is certainly diverse.
Throw in some heavy downpours and a lot of symbolism and it could feel like the beauty of, well, the flowers, is slightly drowned out - literally, in the case of the rain. But actually, in between the layers of meaning, the place is also just gorgeous to look at.
Tightly packed tulips create a mattress you feel you could almost lie on. The aforementioned super-sized biscuits sit alongside huge tea cups overflowing with flowers. Miniature Buddhist temples are festooned in pink and white.
The royals toured a garden created for Sentebale, the charity co-founded by Prince Harry which helps vulnerable children in the small southern African country of Lesotho.
The Queen said well done to the prince, who took a keen interest in the garden's design.
Philip Green, chairman of Sentebale, said: "It is an extreme privilege for us to have three generations of the Royal Family in one garden - for a high-profile but relatively small charity.
"The Queen walked the length of the garden. She was very complimentary about the planting."
Designer Matt Keightley, who created a southern-African theme for the charity after designing a garden for Help the Heroes at last year's show, said: "They genuinely seemed interested and fascinated in the details."
It was Prince Harry's second tour of the garden. When he visited on Monday morning, he said the garden was "everything that I could have wished for".
He told BBC Breakfast parts of the garden were "exactly like Africa".
The Queen was shown a 8m (26ft) sculpture of ceramic tulips made by Paul Cummins, the artist behind last year's poppy display at the Tower of London.
She said the piece was "extraordinary" as she chatted to the sculptor for a few minutes.
Prince Charles and the Duchess of Cornwall toured the show with her sister Annabel Elliot and her husband Simon.
The Princess Royal, the Earl and Countess of Wessex, the Duke and Duchess of Gloucester, and Prince and Princess Michael of Kent also attended.
Some 165,000 people are expected to visit the show over five days and, for the first time, will be able to view the work of an amateur gardener.
Nurse Sean Murray, from Ashington, Northumberland, who won the BBC's Great Chelsea Garden Challenge, has designed a display for the main avenue at the show.
His front garden incorporates both plants and a parking space, to highlight the RHS's campaign, Greening Grey Britain.
It comes after a survey for the RHS showed that 24% of front gardens are now entirely paved, concreted or gravelled. More than a quarter, 28% of the 1,492 people polled, said there was no greenery at all in their front gardens.
RHS principal horticultural adviser Leigh Hunt said: "All gardens are important - vegetation provides so many benefits, preventing flooding, providing homes for wildlife, keeping cities cool in summer, insulating homes in winter."
Joe Swift, BBC presenter of the RHS Chelsea Flower Show, said: "We can all make our streets greener and better places to live and take action against this growing concrete jungle.
"We've made this conversion to grey one garden at a time and now, today, there are 7.24 million front gardens that are mostly paved.
"It's time to get gardening. We can all make a difference: from window boxes to tree planting."