"bob" wrote...
I've a little patch of irises which have been fine for a few years but
the weeds growing between them have become almost impossible to
control so I resolved to dig the whole lot up (I realise this might be
a bit late in the season) and replant.

A lot of the rhizomes have broken off a developing plant. See pic:-

http://dl.dropbox.com/u/10508583/im%201.jpg

-should these simply be discarded or do they have a future for a new
plant?

Throw those all away.


Here is a pic of a new devloping iris.

http://dl.dropbox.com/u/10508583/im%202.jpg

I noted in one youtube video the presenter trimmed the long roots
quite short. Is their any advantage in doing that?

Trim off all the old rhizome with a sharp knife, that's the dark bits
without viable roots

I have quite a few of these

http://dl.dropbox.com/u/10508583/im%203.jpg

- which are tiny and without any rhizome to speak of. Do these
normally survive being dug up and replanted?


Yes they do normally survive as long as you keep the slugs off.
I often pot bits like that up until the spring by which time they are
usually romping away.

It's always a good idea to dig up and replant every 3 years, throwing away
all the weak and old stuff. Best done about 2 months after flowering so they
can get established before the worst of the winter. That said I have to dig
mine all up on the allotment this winter and move them. :-(
--
Regards
Bob Hobden
W.of London. UK