It could be that the brown needles are caused by your trimming. Cutting the buds or needles on a juniper in any fashion will cause damage to the needle tips and browning. I learned this the hard before discovering to pluck new growth with my fingertips. Even accidentally pinching with my fingernails will cause this browing so I am trying to be careful. My junipers grow in full sun in TX and are slowly shedding their brown needles.