Agave americana will survive no, even thrive along the south coast and
in drier southern parts of the UK. Cold tolerance isn't too much of a
problem, but winter wet is a killer. Perfect, exceptionally sharp
drainage is obligatory and any accumulation of water around the roots
or crown is fatal at low temperatures. This species is grown
successfully in many of the southern parts of the UK - especially
where efforts have been made to provide overhead cover from winter
rains. If you are going to attempt this out of doors, select a good
sized specimen (about 2 feet high and across) and plant in a raised
bed of sharp sand, grit plus a bit of garden soil. Be warned, the
spines at the leaf tips are lethal and can deliver a damaging wound if
you brush past, so make sure you plant away from paths etc. The
rosette will eventually grow to around 5 feet high and across.

There was a rather handsome specimen which came into full flower down
on the sea front during this past summer. The 15 foot high flower
spike took a full year to develop and I wondered whether it would make
it through the winter. As the spike continued to grow, the leaves of
the rosette started to die away. Now only the old 'trunk' remains
carrying seed pods aloft, but the original rosette has died, leaving a
few youngsters which will take upwards of 15 years to reach flowering
size. Here are a couple of (rather poor) pics that I took on a very
cloudy day in June - they can be found at:

http://www.ilsham.demon.co.uk/oasis/agave3.jpg

http://www.ilsham.demon.co.uk/oasis/agave4.jpg


Torquay UK