A few years back, I wrote an article called "Why Evergreen IT Must Be Part Of Your Long-Term IT Strategy" which has been one of our most popular blog articles. It defined Evergreen IT as the "perpetual migration of end-user software, hardware and associated services such as mailboxes, telephony, file storage and the infrastructure supporting the technology".
The article also outlined that in order to be successful you have to do three things: 1) implement organizational change, 2) optimize your processes, and 3) invest in technology to manage it all. Those are the three cornerstones on which successful Evergreen IT Management is built.