A head cover trimming system for trimming around a ground level head cover includes a head cap and a grass trimmer assembly. The head cap is provided on the head cover and includes a centering member. The grass trimmer assembly includes a head member having a peripheral edge portion along which is mounted a cutting element. The grass trimmer assembly is driven through a drive shaft connected to a rotary tool at one end. Arranged within the head member is a retractable centering shaft. When the head member is placed over the head cover, the centering shaft is received by the centering member to center the grass trimmer about the head cover. The centering shaft retracts into the head member to allow the rotating cutting element to trim the area around the head cover.