A lawn scarifier, also known as a dethatcher or power rake, is a petrol powered machine used to remove matted thatch from turf or grass.
Thatch is a layer of dead grass that settles on the soil beneath the grass. When the layer of thatch becomes too thick it prevents penetration of moisture and nutrients and stunts grass growth.
The dethatcher or scarifier sends rapidly spinning, thin, vertically oriented blades just to soil level below the grass to rip up the thatch and disturb and aerate the top layer of soil to stimulate healthy growth.
After thatch has been removed, a lawn corer or spiked roller can be used to encourage moisture and nutrients to penetrate deep into the soil and stimulate deep root growth.