I've been trying to grow these things for years and they never get very tall
or have more than a couple of blooms. This year a 9ft monster has emerged
uninvited from a small hole in some paving next to a drain cover.
I know that underneath there is at least 4" of sand, 4" of hardcore, and
then at least a foot of sandy soil mixed with broken glass. I can't imagine
this is a good location for any plant, unless of course its roots have found
their way into the sewer.
Come to think of it though, all the biggest specimens in this area seem to
have self seeded in nooks and crannies. This would suggest that maybe they
need a deep, cool, but well-drained soil and are not too bothereed about
nutrients.
Any thoughts anyone?