Garden & Leisure managing director Neville Prest has left the company following The Garden Centre Group's £18m purchase last month.
G&L finance director Dave Murray is now acting managing director while marketing director John Moseley is also taking over buying.
G&L and TGCG's IT systems are yet to be integrated, meaning buying across the 139-centre chain has yet to be combined.
TGCG CEO Kevin Bradshaw said: "The leadership team at The Garden Centre Group would like to thank Neville for his significant contribution to the Garden & Leisure Group over the last fifteen years.
"Under Neville’s leadership, the business has grown from a single site at Cadbury into a chain of seven high-quality, destination garden centres – which now sit proudly within The Garden Centre Group portfolio. We wish him all the very best in his future endeavours."
Prest said: "I would like to thank everyone at the Garden & Leisure Group for their unceasing hard work and loyalty over the last fifteen years. They should all be very proud of their achievements. I look forward to watching the centres grow and thrive as part of The Garden Centre Group family."