Hi Andy, I think lobelia 'tupa' is a fantastic plant..mine has grown into a beast despite being transplanted when we moved almost four year's ago, it originally came from lower kenneggy.
I have not had any luck taking clumps off it & normally end up with large tuber cuttings instead of something with a nice rootball.
I think once it goes dormant I'll have to dig near the center of the plant for more success.
For me the foliage is as stunning as the flowers.
How tall are the stems on your L. tupa?
Mine is growing in too much shade and rather light free draining soil, not ideal so they only reach max 4ft, I've seen them well over 6ft in more ideal conditions.
I've not attempted to split my clump of the red flowered L.tupa, perhaps I should do that and pamper it a bit more.
You have a very good looking plant there Karl, mine pales in comparison, the red/purple Lobelia to the right of it looks very good too. Do you have a clay soil?
Nice to see you grow Hoheria Charlie, I have grown different varieties and species in several different gardens, and think they are rather underrated. I would grow more here if I had the space.
I love the way sexstylosa sits in the background unnoticed until early July before bursting into flower, when nearly everything else is having a midsummer snooze.
Currently I only grow 'Stardust', it was very easy to train as a standard and the branches less likely to flop over as 'Glory of Almwch' tended to for me.