Kaya Gold outdoor grow Ireland, problem

Hi, I'm new on here and also a first time grower. I have 3 Kaya Golds growing outdoors - I got them because they sounded hardy and well suited for the Irish climate. I planted them early June. One of them is as tall as me and looks well healthy. I went to check on them today - and the other two, within a week and a half, have aquired yellow tips on a lot of the leaves. And any of the new, baby leaves have gone brown and kind of dusty (mouldy?) looking. They haven't grown as much as the other healthy one. The weather hasn't been the best, but it still hasn't seemed to affect the larger, healthy one. Too much rain perhaps? Any ideas what could be doing this? I've given them liquid plant food solution and a small bit of blood, fish & bone a few times. I was surpirsed to see the brown looking leaves today, so any thoughts or advice on this matter would be greatly appreciated, Cheers

J