Scarifiers (often known as verticutters on the continent) perform a task similar to that of a rake; a scarifier uses blades or spring-tines to remove moss, dead plants and weeds that can build up on the surface of the lawn. (See image below)
They often have adjustable blades so they can dig down to cut through shallow roots of grass and thereby help the grass to help develop healthy deep roots.
Many scarifiers also come with an aerating option, and these combi’ scarifiers/aerators can have a swappable cassette for scarifying and one for aerating.
Light scarifying could be done by hand, with a tined rake but this is very hard work and a machine will carry it out more efficiently and quickly.
This task is usually carried out in April and June.