Dan Pearson is not the most well-known gardener in the country, which I think is down to his reluctance to put himself about on TV more than anything else. He is certainly the most accomplished of garden writers, managing to span the globe in his Observer column from Kennington to Hokkaido. But his real skill is in shaping the landscape, and he gave listeners at the VISTA meeting in the revamped Garden Museum, Lambeth, a whistle-stop tour of his career that made me feel in the presence of awe-inspiringly intelligent, artistic thought.

He began with Home Farm, a project that helped to make his name, where he worked to link the ornamental parts of the garden out into the surrounding landscape. Soft wafty planting of gauzy umbellifers framed exquisite views of the English countryside. (There are photos of all Pearson's major projects on his website.) But it was the next project, Gardeners Cottage, that really hooked me in. There, two adjacent walled gardens have been remade by Pearson and his studio, one full of flowers, scents, sensuality and a million bees; the other has been left almost empty, apart from beautiful shaven shapes in the long grass and a curiously beautiful hollow designed for lying to watch the stars.

It was the final images he showed us, though, which most wowed me. In Hokkaido, Japan, Pearson was commissioned to work on a Millennium Forest - so named because it is intended to demonstrate the possibility of thinking about a landscape in terms of the timespan of a thousand years. Here, Pearson carved out landforms that mirror the perfect austere beauty of the northern Japanese landscape, and removed acres of invasive Sasa bamboo to plant 35,000 herbaceous plants in an extraordinary randomly-generated pattern.

"The key," he emphasises, over and over during the course of the evening, "is the staff who will look after the project long-term. It's absolutely vital that you understand who's going to look after it, before you even begin thinking about planning it." And he is clearly in some ways an intensely pragmatic designer; what client couldn't fail to be charmed by a man who says "I'm always trying to move outside my own comfort zone without risking too much of the client's money."

Despite this furiously practical side, Pearson comes across as a man who is still utterly motivated by the dreaminess of gardens. "What I am wanting to create," he says, impassioned, "is a feeling. So that you are seduced by the space you are in. Gardens are place you go into to be in another world, and finding ways to unlock people's imaginations, that's very important. It might just require a really beautiful tree, with really  beautiful space underneath. Because everyone has a memory, somewhere in their childhood, of somewhere they used to go to be alone, to take a friend, somewhere to hide away. Often just a simple thing will do it. In fact sometimes I think the simpler the better."

After his amazing talk, we sat down at long tables to eat roast beef and marvel over what we'd just heard and seen. My mind was full of thoughts. I don't know how such a mild-mannered and modest speaker manages to author such imaginative landscapes; and I don't know how such a great garden designer is lucky enough to also be such a great writer on the subject. But it turned out that down my end of the table there was just one Pearson secret everyone wanted to be let into: How did he get rid of all that Sasa?

For those like me who cannot get enough of Dan Pearson, he is guest editor of Gardens Illustrated in January.