Kew Arboretum head Tony Kirkham, who revealed that a school lesson on conkers got him into trees, said: "I think first of all you need to look at what you are planting and decide what you want to achieve from your planting.
"Getting the right species on the right site is very important. You are better off planting something that's more durable to that site, even if it's an exotic species."
American environmentalist and author Rick Darke said: "I came into gardening from a love of regional landscape, and if we are going to populate the world then we have to work with the world flora.
"If you look at the site conditions you see what works best. Really, if you get serious about sustainability, it's about resource consumption and resource availability. You need to mix global flora - it's very much a permaculture view."
RHS president Elizabeth Banks said: "If you use the British natives you only have about five or six species. I feel there's no issue. If you are trying to do a garden, you don't necessarily have to use natives."
Darke added: "It's really about place and time. There's no real concept of nativity. It's all about how long something has co-evolved with other things."