A Bernese Mountain Dog carries a long outer coat over a dense undercoat. It sheds steadily all year and heavily twice a year, and no amount of grooming stops that entirely. The right routine reduces it dramatically and keeps the coat healthy.
Two or three sessions a week with a slicker brush and an undercoat rake is enough most of the year. Work in sections down to the skin rather than skimming the top, paying attention to the trousers, the ruff and behind the ears where mats form first.
During a moult, daily brushing outdoors saves your house. Bathe only when genuinely needed and dry thoroughly to the skin; a damp undercoat is where hot spots begin.
The mistake to avoid: shaving a Berner to keep them cool. The coat insulates against heat as well as cold, and clipping it can permanently change how it regrows. Manage summer with shade, water and early-morning walks instead.