During a workshop on merchandising, Stein told retailers they "must have a plant guarantee". He said: "It really is important that you put something in place, whether it's a three-year or, I would suggest, even a five-year guarantee. How many people are actually going to bring plants back?"
But delegates rejected the advice, arguing that major retailers might be able to afford to replace plants but smaller players had to use their discretion.
Dean's Nursery manager Sarah Dean said her independent centre aspired to a high level of customer care but could not afford a formal guarantee. "When I think of the winter we have had and then followed by the summer I have had - the weather is going from such extremes," she said.
"We have had customers coming in saying that they have lost plants that they have had for years and years, so I would definitely act with caution before making a statement like that."
Stein raised the issue while illustrating some of the visual merchandising techniques he came across on a recent trip to the USA touring many of the country's top retailers.
He urged delegates to adopt some American retail practices, arguing that the UK garden retail sector could use merchandising far more to boost profits. "Get creative with your displays," he advised.
"Push the boundaries and bring some theatre to it. Don't be afraid to change things if the customers don't like it. And above all, focus on how much you make from each space in your centre. Put a plan together now about how to manage your hot spots."