He is Scottish television’s ultimate evergreen. For more than four decades Jim McColl has shared his infectious passion for gardening with generation after generation of BBC viewers.

But, aged 83, the Beechgrove Garden host has finally admitted it is time for him to lose the plot.

BBC Scotland has announced his oh-so-very reluctant retirement from the show he has presented since 1978. Why? His fingers are still green, but they are not so strong.

Mr McColl explained: “It is time I retired, not because I have lost any interest in gardening or my enthusiasm for gardening, but just because getting old. I’ll be 84 next birthday – so things are going wrong…

“In the sense that if I get down on my knees, I’m not sure I can get back up again. I have to have something to lean on.

“Most importantly, I have a neuropathy thing with my hands. I have no power in my fingers. I have no grip. It has just been gradually getting worse.”

Mr McColl is getting treatment to help with the condition, but has difficulties and is unable to do things like button his top shirt button.

Gardening colleagues watching the show in previous series have also remarked to him that he has been holding gardening tools awkwardly.

He said: “One of the things you want to do when you are showing off on telly, is you want to do it properly.”

Mr McColl formally bows out on a show to be broadcast tonight. Beechgrove, he tells co-presenter Carole Baxter “is half my life.

I just want to grow old in private…but I’ll still garden.”

Mr McColl, from Ayrshire, has been at the helm of The Beechgrove Garden since it began in the late 1970s from the grounds of BBC Scotland’s Aberdeen base. Back then he presented alongside George Barron.

Over the years he has lost count of the number of times he has said “Welcome to Beechgrove Garden” and his catchphrase “Every day’s a school day” is familiar to viewers.

Beechgrove producer Gwyneth Hardy said: “It’s the end of an era for Jim to be handing over the trowel. It’s been a big decision, not taken lightly for Jim as he is genuinely passionate about communicating his knowledge of gardening.

“He said to me recently that, gardening is like breathing for him; it’s an everyday activity. I have worked with Jim for over 20 years and it has been a genuine privilege and an honour to work with a real Scottish cultural icon, who doesn’t see himself in that way, Jim thinks there’s nothing unusual in what he does.

“This makes Jim pretty unique, he has no ego, what you see is what you get and the audience love him for it. That said, even cultural icons have to retire sometime and as Jim will be 84 at next birthday then it’s not unreasonable that he’s thinking of no longer being on our screens. He really has given half a lifetime of service to Beechgrove and our loyal viewers. “

Tonight’s episode will include a look back at Mr McColl’s career on the series.

Beechgrove regular Chris Beardshaw will be on screen later as will another newcomer, Aberdeenshire-based market farmer, Rosa Bevan.

Ms Baxter, who has worked alongside Jim for 36 years, said: “I am going to miss Jim after working with him for all these years but this is an appropriate time to celebrate his career. He is a great gardener and presenter. He shares his wealth of gardening knowledge in a way which engages people at all levels of gardening expertise from none to the professionals.”

Donalda MacKinnon, director of BBC Scotland, said: “Many thousands of gardeners have been inspired and coached by Jim via The Beechgrove Garden over many years and on behalf of them all, and also for other viewers who simply love him for his knowledge and warmth, I’d like to thank him.”

Mr McColl’s life and achievements were celebrated in a BBC Scotland documentary called Jim McColl At 80 in 2015. The programme will be shown again on Easter Monday.

Last week another leading BBC figure, news presenter Jackie Bird, stepped down from presenting Reporting Scotland.