Wisteria feeding?

I've got a 4-yo air-layered Wisteria tree growing in a 10 inch pot currently (same one it arrived to me in 2 months ago). It's wonderfully healthy having seen off a heavy slug attack, & growing crazily (as they do).

However, I'm trying to prepare it for when it'll hopefully be ready to flower and looking to get a name of an appropriate foodstuff for it to that end? Tomato feed has been mentioned but I'm unsure about it for flowering. I currently use bonsai Green Dream and Seaweed fertilizers on a 2-week alternating regimen but again, no idea whether either of these will be suitable?

Can someone perhaps provide actual brand names (UK) of suitable products - thanks?