Published: 00:01, 14 January 2018
"Gardening has helped my wellbeing immeasurably on a number of levels," he reflects. "In terms of physical activity, it is increasingly shown as one of the best and most healthy things that anybody can do."
The Gardeners' World presenter, who has just finished filming Paradise Gardens, a two-part BBC2 series - which is on our screens next week - visiting some of the world's most stunning Islamic gardens, has no thoughts of retirement.
"There are people in their 90s who are gardening well because you have to bend, stoop, lift, twist, turn, walk, reach. It's a full range of movement. Increasingly, people are realising its importance in terms of physical mobility and core strength."
He has said he uses a light box to replicate sunlight in the winter, but getting out into the garden also helps.
"It doesn't matter what the weather is like, if it's a howling gale or rain, being outside in the light and in the air is intrinsically very good for your health, particularly if you are moving around."
"In terms of your mental health, because you growing something, you're doing something positive, even if you are just tidying up.
"Lots have tests have shown that it's really good to spur you on if you're feeling down, will calm you down if you are feeling agitated and make you feel rested and balanced if your mind is jumbled and all over the place - it's a really good leveller for your mind."
Someone weighing around nine stone will burn 150 calories in half an hour of digging, while non-motorised mowing typically burns around 165 calories per 30 minutes, according to research from Harvard Medical School.
Raking the lawn for 30 minutes burns around 120 calories - the same as the calories burned in a half hour of Tai Chi, volleyball and even horseback riding - while half an hour of splitting wood burns the same amount of calories as half an hour of vigorous weight-lifting, research suggests.
Those who squat while they are weeding or planting use a mass of muscles in the process. If you stand on one leg while pruning, digging or clipping, it will stretch you and increase suppleness.
When Monty, 62, suffered a minor stroke in 2008, he took a three-year break from Gardeners' World, returning on condition that the series would be filmed at Longmeadow, his two-acre garden in Herefordshire. Pottering in the garden helped him recover, he reflects.
"I find pruning during the middle of winter therapeutic. The thing about gardening is it's something that takes a lot of your attention but you don't have to think too much about it.
"You have to concentrate but you don't have to worry about the detail of how you're doing it. There's that really good balance between absorbing you and, at the same time, not stressing you."
His latest book, Down to Earth, contains a wealth of information about many aspects of gardening, from growing and planting, to pruning, composting and mulching. Its main message is that gardening is the secret to living well.
But even now, he has to fit his gardening around his work.
"If it's a writing day, I try to write in the morning and garden in the afternoon. If it's a filming day, I start filming at 7.30 and finish at 6, and very often carry on gardening until about 8. At a weekend, I might garden for 12 to 15 hours.
While his overall mental and physical health has undoubtedly benefited from being in the garden, he has sustained a number of physical injuries over the years.
"I took the top of my finger off with a pair of secateurs once. I've always got cuts and scratches. My bad knees are a result of gardening. I've worn away the cartilage.
"If I dig at all, I pay for it with a sleepless night. Sometimes I can hardly walk, but it gets better. I can't run at all now. Any jolting of my knee is bad, and kneeling is not much fun. But I just keep going. I'm still strong and can lift anything."
He doesn't wear gardening gloves if he can help it. "I can't imagine why anyone would. I like to feel the soil. I find gloves just make everything very clumsy. I might wear them if I'm pruning a very prickly rose," adding: "You plant something and it has a future. It needs you. You're investing in a glimmer of hope."
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