Prince of Wales pictured in early days of Highgrove to mark 25 years of gardens opening

The heir to the throne acquired the 18th century countryside retreat and estate near Tetbury, Gloucestershire, in 1980, when it had only a kitchen garden, an overgrown copse, some pastureland and a few hollow oaks.

Charles, a passionate gardener, has spent nearly 40 years devoting his energy into transforming the gardens around the house - which serves as the prince and the Duchess of Cornwall's private home.

The organic gardens opened annually to the public in 1994 and Clarence House said the tours, along with events, retail and catering at Highgrove, have raised more than £7 million for charity over the past quarter of a century.

Some 37,000 people now visit each year.

Another image from Highgrove features Charles, hard at work, planting thyme along a cobbled path which would eventually become the Thyme Walk avenue.

In the background is the prince's beloved pet dog Tigga, who was devoted to his master.

The Jack Russell, given to the prince as a puppy by Lady Salisbury who also helped design the Highgrove gardens, was Charles's companion for 18 years, and the prince was distraught when the dog died in 2002.

Before and after shots released by Clarence House reveal the extent of the prince's decades-long gardening project.

The path Charles was pictured working on featured uninspiring domed yew trees.

At the prince's suggestion, they were later clipped into bold geometric shapes.

The previous wide concrete avenue was replaced with a cobbled path and it now features more than 20 varieties of thyme, alongside golden marjoram and primroses.

The main lawn is edged with a striking topiary yew hedge, designed by historian, writer and garden designer Sir Roy Strong.

Other then and now images show the early days of the Sundial Garden created by Charles and Lady Salisbury which is set with a stone sundial at its centre, surrounded by a rose garden.

It now features box hedging and beds planted with towering blue, pink and purple delphiniums, and willow sculptures.

Other highlights at Highgrove include The Stumpery, with its tree stumps, ferns, wood carved sculptures and oak temple.

It also has a thatched tree house known as Hollyrood House - which was built for Prince William's seventh birthday in 1989, and later refurbished for Charles's grandson Prince George when he was a toddler.

Meanwhile, the classic Cottage Garden, inspired by the colours of yellow, pink and blue Tibetan silks, features spring and autumn flowering bulbs and an oak summer house, co-designed by the prince.

Charles has also ensured rare trees and plants have been grown for future generations to enjoy and heritage seeds planted to make sure the varieties continue to flourish.

A Wildflower Meadow stretches out across four acres in front of the house.

The prince has said of the gardens: "One of my greatest joys is to see the pleasure that the garden can bring to many of the visitors and that everybody seems to find some part of it that is special to them."

All profits from the sale of Highgrove products, garden tours and events are donated to the Prince of Wales's Charitable Fund.

The grant-making body supports projects by a wide range of organisations including Streetwise Opera, which helps people at risk of homelessness, and Big Kid, which helps young people at risk of social exclusion and youth violence to take control of their lives.

* The gardens are open to individuals and groups from April to October every year.