How to turn 8000 plants into a Van Gogh masterpiece

I’ve just been to London’s Trafalgar Square to check how the ‘living art’ on display outside the National Gallery is doing. Van Gogh’s 1889 painting of ‘A Wheatfield with Cypresses’ has been recreated with more than 25 varieties of plants, and although the colours in this living wall aren’t all perfect matches, as the foliage grows, it’s looking pretty good, and attracting much attention from passers-by.

For those not quite sure how the original looks, there's also a copy with an explanation. I wonder what the artist would have made of it all?
The living painting will be on display until the end of October.