Perennials last throughout the year, but unfortunately most perennials tend to go dormant during the winter months.
If I had few acres of food plot, I would focus most on fall/winter annuals planted in fall.
If I had considerable acreage in food plots I would have 40% in perennials and 60% in annuals, both spring/summer and fall/winter (requiring planting twice a year--spring and fall).
Perennials have the advantage of not having to be replanted twice a year or even each year. Annuals have the advantage of producing more forage during the seasons targeted.