This is something I've been thinking about a lot. With the one I'm currently flowering, the Panama rootstock plant was left to flower as a third of the plant along with the two scion strains that were grafted on to it.
When I was reading about commercial grafting, I read that they apparently never leave any of the rootstock foliage to grow or it will quickly take over from the scion. So any shoots that grow out below the splice are always removed.
In my case the Panama didn't 'take over' from the other two- though I had to work at it to keep the three sections a roughly equal size- and the Panama took more pruning and slowing than the other two.
Anyway- part of me is wondering if it has changed the dynamic somehow that I haven't removed the rootstock foliage. Maybe it would be having more influence on the other two if I did it the 'normal' way. I can't really think how it could- since the only roots growing in the pot are the Panama roots, and everything flows through her stem initially.
I'm going to test this more when I flower the Peyote Purple- G Tiger, Honduras, Malawi, Panama.
So far I have the Honduras grafted on to the PP already, and the GT and Pan are almost done and ready to cut free. After the Malawi is grafted on I'll remove all the PP branches and foliage- leaving just the base that feeds the other four strains growing on it.
That's going to be a really uneven mix so I hope there's some sort of major influence and calming effect from the rootstock or its going to be a bit of a gong show trying to sort that one out.
I don't know what I'm going to do with the other multi-strain hydra I have in veg. I suppose I'll have to either keep hacking it down and use it as a mother- or flower it and hope for the best. It keeps trying to overgrow my veg room and it's kind of a bushy confusing mess. Little labels stuck all over the place so I can know what branch is what. Part of me wants to say f it and toss the thing into flower just to get rid of it.