Thatch builds up over time, so it's not necessary to dethatch every year. It is best to dethatch every couple of years. Some lawns may need it more often than others. You might want to check your lawn every year to see how much thatch has accumulated.
We will be using a JRCO heavy duty spring tine rake dethatcher attached to an Exmark 60" zero turn with a bagging system. This setup allows for efficiency and enables us go over the property multiple times to get all the matted dead grass. This may also be used for spring clean ups to help the grass achieve an early greening by allowing the turf to breath.