Cherry Laurel Burnt Leaves or disease

About 6 weeks ago I planted a new hedge of Cherry Laurel, some of these have started to show a slight brown around the outside.  Some on the other hand appears appear nice and vibrant green.  All appear to be producing new buds.

I must admit that I've only watered them probably once each week, so I'm wondering if the browning to the leaf could be through lack of water or a disease.

Here's a pic which shows what some are looking like, any thoughts would be most appreciated.