Speaking to delegates at last week's Landscape show in London, Gregory called trade representation for landscape contractors and designers "fragmented" and said there should be greater unity.
"I want to work more closely with the Society of Garden Designers and if I had my way BALI and APL would be one," he added.
"We should have one trade body and there is a willingness to do it. It's not going to happen overnight, but we are a lot closer now than we were a few years ago."
Gregory's comments came during a delegate debate after his lecture on the relationship between landscape contractors and garden designers, in which he called for tougher regulation in the industry.
"Our trade is unregulated - it's a tramps' trade," he said. "Anyone can call themselves a garden designer or a landscape contractor and charge whatever they want."
Gregory added that garden designers were beginning to take over much of the work traditionally carried out by landscape contractors and lack of regulation was allowing them to heavily undercut their competition leaving landscapers with less work.
"Contractors need to become profitable and designers must work for a proper commercial fee instead of taking kickbacks from contractors or working for tea and biscuits as some do. It is undermining the profession," he said.
Gregory also called for greater collaboration and "honest dialogue" between contractors and designers on how work was divided up.