You can hear David asking at 35:20 in the BBC Radio 4 program Gardeners Question Time first broadcasted Friday 18 January 2013.
http://www.bbc.co.uk/programmes/b01pw5sd
The original copy text is under all these 10 orginal photographs taken by Phil Yeomans/BNPS published 21 Jan 2013: http://bnps.photoshelter.com/gallery/52-year-old-sealed-gard...
There is also a close up of the seal: http://bnps.photoshelter.com/gallery-image/52-year-old-seale...