Post science not speculation.
...clear glass encourages the growth of algae...
The bottle garden should be cleaned inside and out once a month.
Algae growth tends to be rapid in bottle gardens... This monthly scrubbing and cleaning out is the key to the whole success story.
Source: http://books.google.com/books?id=rSiFAAAAQBAJ&lpg=PT522&pg=P...
and: https://news.ycombinator.com/item?id=7858411
It seems the story is indeed disingenuous. Thanks for posting.
Post science not speculation.