I T’S the instant visitors walk into the ‘new’ walled garden, built in 1760, that they finally understand the love and care that has been poured into Wallington during the past 300 years.

“You have probably been pleased with what you’ve seen so far,” said head gardener John Ellis, “but if this is your first visit, this is your ‘wow!’ moment.”

And by God, he’s right. There’s the garden within, designed by the man oft described as the greatest landscape designer of the 20th century, Graham Stuart Thomas, and the Owl House that bears the hallmark of probably the greatest one of all time, Capability Brown.

There’s the Edwardian conservatory and its fantastical blooms that together are regarded as Wallington’s winter Garden, and the borders surrounding it bearing the hot colours that speak of Gertrude Jekyll.

And then there’s the ornamental pond and curved staircases that were, in essence, a goodbye gift from Lady Mary Trevelyan, given when her husband, the aristocratic socialist politician Sir Charles Trevelyan, decided to hand the property over to the National Trust in the 1930s.

If you were to quibble with John Ellis, it would only be to say it isn’t just the first-time visitor who is struck by the sheer beauty of the sight that unfolds as you step through the Neptune Gate set in its ancient walls.

As the seasons roll around, the ever-changing vista never ceases to enchant and amaze.

But after 26 years as head gardener at Wallington, he wouldn’t disagree. His own favourite view is that offered by the Owl House – where he had his office for many years – looking across a verdant meadow to the Palladian Paine’s Bridge, designed by 18th century architect James Paine.

John said: “This is one of the naturalistic views Capability Brown would have approved of, complete with rolling fields and water.

“The Northumberland countryside is said to have influenced Brown, but I like to think he actually recreated Northumberland wherever he went.”

While John is preparing to retire from Wallington and the National Trust (or semi-retire, because he plans to do some freelance work), he leaves knowing he has made his own mark, too.

The beautiful and meandering winter walk through the woodlands fanning out from Wallington Hall is his creation.

Trees have been thinned to allow dappled sunlight to fall to the woodland floor. Colourful varieties such as snake bark acers and red panda birches have been planted, and 200,000 snowdrops have been sown to dramatic effect.

“Perhaps with the seasonal attraction of gardens, people think there’s nothing to see during the winter, but there is at Wallington,” he said.

“I spent a week driving round the country looking at other gardens of winter interest, from Cambo House near St Andrew’s, which is known for its snowdrops, down to Hampshire and the Sir Harold Hillier gardens, which include the largest winter garden in Europe.

“I did over 1,000 miles and then came home not to copy what I’d seen, but to use the ideas as a springboard. “Maybe the fact our conservatory was built as a winter garden for the Trevelyan family has given us a licence to carry on creating winter wonders.”

Having previously worked at places such as the Oxford University Botanic Garden, the National Vegetable Research Station – which was established in Warwick during the Second World War to improve food production – and Pembroke School in Wales, where he was tasked with teaching young people how to grow and sell food, he found a real contrast in approach when he arrived at Wallington in 1990.

“When Sir Charles died in 1958 and the National Trust assumed full management of the estate, rightly or wrongly it transformed what was the kitchen garden in the walled garden into an ornamental garden,” he said.

“There would have been no interest in vegetables as a visitors’ spectacle – there is now, but not then.

“We’re not fixed to a particular period in history here because, really, it’s an 18th century pleasure garden with a lot of 19th and 20th century overlay.”

The fact that for the majority of John’s time at Wallington, Sir Charles and Lady Mary’s daughter, Patricia, was still in residence in Wallington Hall had meant a lot to him.

That sense of connection to the Trevelyan family had made a big difference to the staff in general.

“She took a keen interest both in the people and the landscape,” he said. “And although I actually worked for the National Trust and not directly for Patricia, I never wanted to leave here while she was alive. I felt a lot of loyalty to her.

“We used to invite her to our staff socials, which she loved. The last thing she wanted to be was isolated. She’s been a great loss.

“Her family is still involved with Wallington, of course – her daughter, Janet, was here just yesterday.”

Patricia Jennings, the last Trevelyan to live at Wallington Hall, died in 2013 at the age of 98.

The estate has only had two head gardeners since the National Trust took it over, and John knows his predecessor - Geoffrey Moon, who is now 90. Today, Mr Moon’s daughter, Emily Johnson, works as a ranger at Wallington.

John said: “In 1958, we were lucky in that we had Graham Stuart Thomas as head of the National Trust gardens nationwide – many people regard him as the greatest gardener of the 20th century – and people here remember him visiting right up until the mid-1970s.

“Geoffrey would have been following his plans for the transformation of the walled garden and the other work done around Wallington, and I have been building on that vision ever since.”

A botanist known for his love of roses, by the time Graham Thomas OBE died in 2003, he had restored and held stewardship of more than 100 National Trust gardens and written 19 books that are the epitome of horticultural know-how.