A variable arc sprinkler head or nozzle may be set to numerous positions to adjust the arcuate span of the sprinkler. The sprinkler head includes an arc adjustment valve having two portions that helically engage each other to define an opening that may be adjusted at the top of the sprinkler to a desired arcuate length. The arcuate length may be adjusted by pressing down and rotating a deflector to directly actuate the valve. The sprinkler head may include a lock-out feature to prevent adjustment. A method of irrigation is also provided involving moving the deflector between an arc adjustment position and an operational, irrigation position. The sprinkler head may also include a flow rate adjustment valve that may be adjusted by actuation of an outer wall of the sprinkler. Rotation of the outer wall causes a flow control member to move axially to or away from an inlet.