Devon,
United Kingdom 
After planting Acanthus 4 years ago it still hasn't flowered. Originally in a part shaded bed, i moved it to a sunnier position after 2 years. That was 2 years ago and although it has grown well and is very leafy it still isn't flowering.
I don't know whether it's just me but my Phlomis/Jerusalem Sage took four years to start flowering. Is it my garden that is lacking?
22 Jul, 2017
Answers
Hi
Your soil maybe too rich and is creating too much foliage, do you feed the plant if yes I would stop and see what happens next year as the flowers should of shown by now as mine is in full flower and grows in a sunny spot but contains lots of rubble but thinking about it did take several years to settle in before producing any flowers.
23 Jul, 2017
My Acanthus is flowering beautifully this year but the two years before that I had nothing. When I first got it I had no flowers and then it just happened. I have no idea why. I thought it might be enough sunshine at the right time. Who knows? I gave some to a friend and he gets continual flowering.
23 Jul, 2017
Well my Phlomis flowered straight away but my Acanthus never flowered at all. It didn't feel the need to set seeds because it spread so vigorously by runners - took me several years to get rid...It eas shaded in the morning and full sun the rest of the day.
22 Jul, 2017