Speaking at the Southport Flower Show, which attracted 80,000 visitors last week, Buczacki said: "It has not improved since I spoke out.
"But the BBC is always right and doesn't respect anyone else's point of view and can't take criticism - they are entitled to their opinion and say 'our audience still love us, so that will do'.
"But there is no longer a gardening programme for the serious or even semi-serious gardener."
He blamed the change of producer, which replaced Rosemary Edwards with Andy Vernon this spring: "It has become trivial, silly and irrelevant by trying to mimic Top Gear and Blue Peter - and if you trivialise, you lose credibility.
"The presenters may be knowledgeable horticulturists so they don't need to do stupid things such as silly interplay like amateur actors."
He added that the programme does not cover "90 per cent" of the essential gardening jobs he thinks should be discussed each week: "If it's time to sow runner beans or prune apples you need to know.
"But over a period of three weeks there was not one job I considered essential that appeared."
A BBC representative replied: "Gardeners' World remains the seasonal, hands-on gardening programme that it always has been and it continues to cover as many essential weekly tasks as it can within its current 30-minute format. The series aims to inspire as many people across the UK as possible to get out and enjoy themselves by escaping to their garden, and our vast range of content seeks to cater for as many gardeners as possible.
"The core values and passion of the programme have not changed and, as always, we have an expert presenting team of truly passionate and qualified gardeners who reflect different styles of gardening."
She added: "Greenacre is still a garden in its infancy and there are many projects we intend to introduce in the future.
"The series is broadcast across the year, breaking only for major events that may over-run, including athletics programmes, the Proms and Wimbledon, but this is not a new departure."