The term "in season," in reference to produce, is something people intuitively understand. When cherries are in season in the late spring, they have dark, soft flesh, bursting with juice and sweetness. Out of season, cherries tend have paler, crisper, dryer, and less sweet flesh that stubbornly clings to the pit. "In season" for coffee, as we will see, is a bit more complex than it is for cherries, but just as essential.
Coffee grows best in high elevation equatorial zones with lots of predictable rainfall - collectively these zones are referred to as the 'coffee belt.' Like cherries, coffee also grows on a tree. In fact, the fruit of the coffee tree is even referred to as the 'cherry' due to the strong resemblance. The coffee belt, which straddles the equator, includes origins as far north as India and Mexico, and as far south as Bolivia, Tanzania, and Papua New Guinea.
Because the seasons reverse across the equator, there's a variance in seasonality within the coffee belt: when it's winter in Bolivia, it's summer in Mexico. To add to the complexity, origins may have shorter or longer harvests due to local microclimate, or they may use different coffee tree varietals that have different growth periods. The result of all of this complexity is that there is essentially always coffee that's 'in season.'
It doesn't end there though - coffee has more wiggle-room in terms of maintaining quality than a spring cherry does - and that's because we're not interested in the sugary, perishable flesh of the coffee fruit (at least not right now- dried coffee flesh can make a lovely tea called cascara), we're interested in the seed. The seed requires several weeks of drying, resting and processing post-harvest, followed by several more weeks or more on a cargo ship. Generally it takes a couple months after harvest for coffee to reach your cup - and that's okay.
A several week resting period is necessary for physical and biochemical processes to take place in the bean that improve it's quality. What's not okay is receiving coffee that's 9+ months off harvest. At this point, the moisture content in the coffee bean has diminished and the coffee begins to taste "age-y"- think woody flavors like cedar. Large mega-roasters get around this age-related defective flavor by roasting it darker. A dark roast will easily hide years of coffee sitting untouched in a warehouse.
The main takeaway is that the "in season" status of coffee differs depending on the origin and depending on where you are in the world, coffee from certain origins may take a little longer to get to you. The best thing you can do is understand the harvest schedule which you can find here - courtesy of Nordic Approach.