Standard PhotiniaNnot Thriving

Annie S

I planted two standard photinia 'little red robin' two years ago in our north facing front garden. Both we purchased at the same time and are planted about 10m apart. One plant is thriving, making plenty of growth and generally looking well, whilst the other is poor, with slow growth and several areas where the wood has died back. Can anyone offer advice on what might be causing this and any solutions? Many thanks

Dovefromabove

Any chance of photos, of the individual plants, plus some of the whole area so we can see what there is around them that might be causing a problem