Power raking is the best way to remove thatch, dead grass and debris that has built up on your lawn over the winter. Removing thatch and debris allows for better absorption of water and fertilizer into the soil. Ideally power rake before over seeding to allow easier germination of new seed resulting in a greener , healthier lawn. In Calgary the ideal time is April 1 to May 15 which is right before grass enters its period of strongest growth.