All grass lawns produce a layer of dead material called thatch, which falls between the grass blades and lies on the surface of the soil. Thatch builds up becoming matted and preventing the grass from regeneration, effectively choking the life out of it. It also prevents water and nutrients getting to the root zone, acting like a barrier and providing a haven for fungal diseases.
Scarification should be carried out periodically to remove this layer of thatch, although sometimes it is necessary to scarify more frequently if this layer has been left to build up for a long time or your lawn grows particularly fast.
A commercial scarifier will be used to ensure this process is completed thoroughly so the lawn renovation is a success. Typically scarification is carried out in early spring so the lawn can recover by summer, but if necessary it can be completed in the autumn to facilitate recovery through the colder months, ready for the following year.