Abstract: A flexible line trimmer attachment for a tractor driven mower deck for trimming around trees and other objects simultaneously with mowing. A pivotal boom projects laterally from the mower deck and carries one or more trimming heads which rotate flexible lines using motive power supplied by the tractor. The boom deflects when it encounters a tree and is able to trim around more than 180.degree. of the tree circumference. A tension spring returns the boom to its normal lateral position after the tree has been cleared. The boom can be swung upwardly for compact storage by a power cylinder.