We use a Classen TR-20 like the one above and to the right. TR stands for turf rake. Turf rakes are commonly referred to as dethatching machines and are also called power rakes. Although it is most often referred to as a dethatching machine, turf rake is more accurate because it can do more than just dethatch a lawn.
An axel on the underside of a dethatching machine spins blades that slice into thatch, moss, pine debris and soil. An appropriate depth can be accomplished by raising or lowering the deck of the dethatching machine.
The canopy of the grass in the video is very thick. Just below the surface is a layer of thatch. It's so thick that it's difficult to touch the soil. When grass is rooted in thatch rather than soil it is more vulnerable to environmental changes. Thinning a lawn such as this will help direct water, fertilizer, and roots into the soil. It will also reduce an ideal habitat for crane fly grubs which feed on grass roots. If excessive thatch goes unchecked for too long it may begin to look brown and patchy like the two pictures below.
Dethatching machines are intended to dislodge dead and horizontal unrooted material while leaving healthy rooted grass. After the lawn is dethatched (above picture) the debris that remains must be removed from the lawn's surface. The general condition of the lawn should be taken into consideration when choosing how aggressively to dethatch. For example a mostly healthy lawn with a minimal or moderate amount of thatch (above picture) should receive a lighter touch than a matted thatch lawn like the one in the video below. The goal is to get as much unhealthy debris out while minimizing the damage that's done to healthy grass so the lawn can recover quickly. Finding that balance is the key to a job well done.
Canopy thatch that is not addressed can progress to become a layer of thatch that is matted to the ground. Grass seed is unlikely to root when sown on matted thatch. Even if it did it would not be resilient. To reestablish turf the matted thatch needs to be removed so the seed is in contact with the soil. The video above shows matted thatch before and after the using the machine.
Moss is common in lawns near landscaped edges. These areas tend to be a shady moist environment that moss prefers. Mulching beds will help prevent moss from creeping into the lawn.
Moss can effectively be removed from lawns with at dethatching machine. For best results a moss killer product should be applied a couple days before it is dethatched. Dead moss will be black or brown and much easier to remove. Once it is removed overseeding is recommended to replace the moss with new healthy grass.
The video above is of a lawn that was under a pool. A seed bed was cultivated where the pool was using the dethatching machine. Notice the fine soil in the upper half of the screen made by the dethatching machine. The machine scratches 1" wide rows in the soil aiding germination.