Hi, how long have you had them, and have they previously flowered well ?, some so called hardy Hibiscus, don't flower very well at all, they just about survive a winter, and start into growth late in the season, but if they have been ok in the past, feed them with a fertilizer higher in phosphorus, and less nitrogen, look at the N P K on the packet, you need the N to be lower than the P and the K to encourage flowering, Derek.

In my experience, more potash is more effective than more phosphate--that may only be an effect of our alkaline soils, though.

Hi Tugbrethil, of course you're right, I don't know why I said phosphorus, must have had a 'senior moment' lol, glad you pointed out the error, Derek.