I have not finished my first full season but from what I have read in the FAQ the crops should stay in your inventory for as long as you save them. The crop cards themselves (the seeds) will not deteriorate after you harvest them. From the time you plant them initially they will start a 14 day cool down period where you can not plant them again until the cool down time has completed. I will be doing an update after the Winter season ends on dCrops. Thank you for your interest in my initial post!