His Easigrass Urban Plantaholics kitchen garden attracted a few disapproving comments for introducing artificial grass to the RHS Chelsea Flower Show for the first time this year but, as Smith explains, it was never his intention to wind people up.
"There are two angles. From the show organisers' point of view, intellectually, they need a range of different gardens and styles and they need some stories because that helps to make the show. It's like going to the West End - you want something spectacular. But from my point of view, I have absolutely no choice in it because they are just ideas - this was the idea. It wasn't asking how I could stir things up and provoke people with artificial grass."
In fact, the garden took shape when Smith was working on a project last autumn alongside Easigrass managing director Anthony Gallagher. "Anthony came to me and asked: 'Can we do Chelsea?' and I said: 'Yes.' That's why there's artificial grass here - I responded to his brief. With my other gardens there has been absolutely no intention to shock. It just so happens my ideas are a bit left-field, I suppose.
"I'm not stupid, I know that it doesn't do me any harm. What I have got to guard against is thinking about the reputation by playing it safe, which a lot of people do - or over-egging it, just for effect. The thought of doing a flower show and nobody noticing my garden is horrific - I wont deny it - but controversy is definitely not my motivation."
Either way, it seems to be working, as each design attracts more comment, good and bad, and corporate sponsors get the oxygen of publicity they crave. But there is a wider debate about what a garden at Chelsea should be and Smith's gardens often find themselves in the centre of this, too.
A developing theme in his designs is his use of a narrow range of plants. His Chelsea and Hampton Court gardens for Quilted Velvet last year used some types in large volume - pink Impatiens and oak seedlings.
His conceptual garden at Tatton Park this year will be made up entirely of lettuces, to create a lunar crater, and even the Easigrass garden uses only orchids, ferns and bedding.
The rationale, he says, is to look at the garden and the concept and to decide how removing a plant would affect it, to ensure that everything in it has a reason to be there and that it says something.
This bold use of plant material is an integral part of Smith's highly conceptual designs, which leave his critics questioning whether his exhibits should be truly termed "gardens" at all.
But Smith is unmoved by such voices, jokily suggesting his response might sound like something the actor Russell Crowe would say to a critic. "That's not why you should do it. If you have a client who wants a garden to live in, I give them a garden to live in. If you have a client who wants a show, I give them a show. You have to draw the line," he insists.
"Yes, there are ideas you can draw from show gardens, and most things I have done, you could actually do - with some tweaking - but that isn't the rationale behind it. The rationale is to put on a show and to realise a concept.
"I have been criticised before because people say I shouldn't be at a flower show, I should be at Tate Modern. Well, that's a huge compliment for me. My answer to that is always, 'Come on then, where's the invitation?'
"Basically, to me it's art - there is no separation between what I'm doing here and what's in Tate Modern - and I do make sculptures and do installations but at the moment, because of my reputation, the gardens pay better."
While he has strong words for his critics, Smith is full of praise for the spirit of open mindedness he has found at the RHS, which is often accused of stuffiness. "The problem it has is it has a long history and a very strong brand and it can't take huge risks," he explains.
"But it does take risks all the time. It took a chance on my Iraq War installation here at Chelsea and the press were all over that - talking about the morality of the war at a flower show.
"It has been very fair-minded with me. When it has turned me down it has had sensible reasons, which I was already half aware of. So I have tested it. I have seen how far you can push and you can push it as far as is reasonable. I probably will keep pushing because if I have an idea, I can't let it rest."
Next year may see him push it further as, together with Gallagher, he is hoping to produce a full-scale show garden for Easigrass in 2011. This year's effort will certainly not be the last that we will hear of him.
"There are a lot of things in the pipeline, I have a lot of ideas that don't involve plants and I have a lot of ideas that do involve all plants. To me, why pen yourself in by saying: 'I'm a garden designer and I do sensible' - where's the fun in that? So the whole thing about 'is it relevant?' - no, it isn't. Whether it's relevant or not, you just do it."
2000: Establishes Hortus Infinitus
2005: Sensory school garden at Hampton Court wins silver gilt
2007: Gold and best in show for Hampton Court conceptual garden
2008: Gold and best in show for Hampton Court conceptual garden
2008: Iraq War installation at Chelsea. Star art installation at Hampton
2009: Quilted Velvet garden at Chelsea wins silver
2009: Quilted Velvet gardens at Hampton Court and Tatton win gold
2010: Urban Plantaholics kitchen garden at Chelsea
2010: Visionary garden at Tatton Park