The Klondyke chief executive said: "I felt personally it was a very positive move appointing Carol Paris as HTA director general [replacing David Gwyther after 16 years in the role] and I was more than happy to give my support by becoming a board member.
"There are positive days ahead for the HTA. I hope links between the GCA and HTA can be closer. With Carol Paris as figurehead I see no reason why some of the differences of the past should not stay in the past."
Paris said after an "awful year" garden centres have to " adapt to grow" and "collaboration is a key theme".
Gardman CEO Mark Pearson and Roundstone managing director Peter Cook have also joined the HTA board to add to existing members Ian Ashton of Lowaters Nursery, Stan Green of Growforth Ltd, John Lord of John Woods Nurseries, David Norman of Abercorn Plant and Garden Centre, and Caroline Owen of Scotsdales Garden Centre.