Later, I recount the visit to my mum.

My mum: "Ha ha! That’s true actually. I've read about four articles in the paper about that crack, and none of them were anything about the meaning of it. Actually they were all by builders, speculating on how she might have done it. Apparently it's to do with ****** and **** ************. "(censored for your own good - see below)

So whatever it means, however it was made, absolutely nobody is talking about how this crack really sums up for them the big chasm between white and non-white peoples.

It seems to me that the crack really doesn’t speak as loudly on the subject of race as its creator would have wished. But it does seem to be talking with voice raised when you think about it in relation to another show on at Tate Modern at the moment – The World as a Stage.

Jessica Morgan and Catherine Wood have created an exhibition about theatricality in modern art. Which is how we (eventually) get to gardens, because theatricality is such an important aspect of garden design. Think of the gasp of breath you are meant to draw when, after walking through a wonderful garden, you finally see a stupendous view of three counties / a thousand acres / distant hills.

The Tate crack takes theatricality one step further because it amazes and foxes us. Like a magic trick, it makes us wonder how on earth the effect was achieved.

Me to Tate employee: "That's really annoying you can't tell us."

A passing stranger: "The only possible explanation is... magic?"

Certainly, whatever the professed ambitions of Doris Salcado, she is behaving like a true member of the Magic Circle, constructing her crack behind secret hoardings for some six weeks before her "dun-da-nah!" moment.

Gardens used to have this element sewn up in the Baroque period – Solomon de Caus was famous for his sculptures that suddenly spat out water. He once invented a water-powered merry-go-round that turned out to the sound of an invisible pipe organ. And his trompe l'oeil was said to be so good it actually fooled birds. 

I would love gardens to have this kind of quality again - the kind that makes people stop and wonder how on earth it was done. We only have a little of that sense of foxedness left in gardening; one area it remains in is mazes. (Mazes are still something which fascinate people – signs to the Maize Maze proliferated across Sussex this summer, I noticed.)

We enjoy being played with, as long as it's not too sinister. I don’t go into a maze with a map. I don't necessarily want the illusion explained. And after some reflection, I’m glad I don’t know exactly how the crack was made.

(PS if you absolutely insist on disobeying Doris, read on:

http://arts.guardian.co.uk/art/visualart/story/0,,2187568,00.html)