Mr McColl, who hosted the popular show for more than four decades before stepping down earlier this year, said the changes made by the corporation left him feeling that he was right to leave.
The 83-year-old, who first helmed the programme in 1978, accused BBC bosses of lacking “common sense”, let alone any knowledge of gardening, after paring back the number of episodes from 26 to just 14.
Writing in a column for the Press & Journal newspaper, Mr McColl, who was honoured with a Royal Television Society Scotland award in 2016, said the decision had caused a “furore”.
He said: “Why move it to the new channel when it was fine on BBC Two?
“In the meantime, there is a veritable host of gardening programmes made in the south broadcast into Scotland every week, summer and winter.
“There will be a total of 14 programmes, reduced from 26 which covered our growing season nicely, but what do these guys in Glasgow know about common sense, let alone horticulture?”
Mr McColl, from Oldmeldrum in Aberdeenshire, said he had made his decision to retire before the scheduling changes were confirmed, which left him realising that “I just got out in time”.
“I think the very loyal viewing gardening public has been betrayed by BBC Scotland,” he said.
“The programme content has been, and still is, first rate and appropriate to Scottish conditions.”
He added: “Since word got out about the number of shows being cut, it’s caused a significant furore on social media.
“Not surprisingly, show supporters are not too chuffed with the new scheduling and have already made their feelings known.”
The show is produced for BBC Scotland by Tern Television and more than 1,000 episodes have been aired over the years.
A companion show, entitled The Beechgrove Potting Shed, was broadcast weekly on BBC Radio Scotland between 1978 and 2012.
The show’s cultural reach has also seen it parodied over the years by comedians including Rikki Fulton and Gregor Fisher. A spokesman for BBC Scotland said Beechgrove Garden continued to be a “well loved” part of the channel’s output and said more gardening advice was now being made available on the radio and online.
He said: “We are no longer able to opt-out of BBC Two as we now have the new BBC Scotland channel.
“Beechgrove is a well-loved part of the new channel’s schedule and the programme also continues to get an airing on BBC Two. In its new format, Beechgrove offers more online and social media content, available at any time.”
He added: “The presenters are also offering advice on Grow It on BBC Radio Scotland, so our audiences will continue to benefit from their expertise during the summer.
“Beechgrove returns at the end of July and, in the meantime, we hope our audiences enjoy its digital content.”