Buxus hedging turned brown

i planted some Buxus hedging on each side of my drive way last year. in August/September some of one side turned brown/coppper. i gave it some feed and pulled back some of the bark mulch that i put around them in case they werent getting enough water. they are still alive so i was wondering if there is some feed i should be putting on them now to help them along. i read that some buxus can be affected by a blight or lack of Potassium. the lawn beside it can be wet at times also, so i know that this doesnt help it.