Hi Elfi,
Your tibouchina needs to get aclimatised to your situation. It may take a few more weeks to get going, so try to wait for it. To much fertiliser will only make a flush of green growth. To much shade will also slow them down. When they take off, you can prune them to shape. Good luck. Peter r

Yes though they will flower when young, sometimes just a little patience for them to get established. Sometimes you will get two flushes a year I wouldn't be too desperate to cut it back, that's really only necessary to tidy them up every couple of years and keep them more compact (if that's your aim). I haven't found that regular pruning does much either way for flowering.

Thanks Peter for your advice. I've actually still got the shrub in the pot as I wanted to keep it near the house for the time being while there might still be some slight frosts and we have got quite a bit of wind here. Would you advise to put it in the garden already now where I want it to grow???

Hi Elfi,
Good time for planting out now, if you don't have water restrictions. Good luck. Peter r