never heard of it bertiefox. 20ft wow that is one heck of a dahlia.

I just googled it bertiefox. the tuber is hardy down to minus 6. like typical bedding ones they are knocked back by the frosts. so if you get frosts before nov where you are you wont get the flowers.
from what i have read you treat it like all the other types. the flowers are pinkish and can be up to 6" in diameter.

looks impresive. :o)

We didn't pay much attention to Dahlias - until we went to the wonderful garden at Yewbarrow House near Grange-over-Sands in Cumbria. The row of Dahlia Imperialis there looked amazing - even though they had no flowers.
The massive main stems had a "milkmaid's yoke" effect where the leaf stems branched out at regular intervals up them.
We now have one in the garden and it looks great (at least until lately when the frosts cut it down). We'll see if it resprouts again this year.
Flowers are unlikely (unless we have an incredibly long hot summer), but we're happy just to have such architectural foliage.

Thanks Seaburngirl and Longleaf.
That sounds encouraging as if it flourishes in Cumbria it should grow well here. I read somewhere it will withstand minus 6 if it's well mulched, but I'll probably dig up the tubers before the winter.
As we have a rather longer season here I might well be able to enjoy some flowers... in a good year we can still have no frosts and warm weather into November. I managed to fruit a 'Courge de Siam', cucurbita vitifolia, which never did anything more than produce leaves in the UK.
Nice to hear someone has seen dahlia imperialis growing in the UK.
I will let GOY know if/when it flowers (assuming the seeds germinate!)

Just a progress report on my Dahlia Imperialis. I put some in 14 inch pots, but that's nothing like big enough for this plant which makes enormous bamboo like stems. The ones I've planted in open ground are doing much better so I will probably leave them to grow as far as they can this year and then mulch heavily for winter protection. If I get flowers this year it will be a bonus.
I'll keep the pot grown ones indoors over winter and at least I'll have some tubers to give me a good start next year.