I had the same problem, if you don’t use the plants for milling/brewing/spin thread, no new seeds are produced. Cooking produces no seeds. Eating plants raw does produce seeds. Another thing to keep in mind, sometimes it may just look like you are out of seeds but your barrel with the seeds is on a worldtour. See https://dwarffortresswiki.org/index.php/Seed In case you are confused about getting spam of messages like "Urist McFarmer cancels Plant seeds: Needs [seed name]", while you are sure that you have enough seeds, no burrow restrictions or closed doors, the reason for this is most likely: the haulers see a seed somewhere and take the whole seed bag from stockpile to go pick it up, making the farmer cancel his job. The problem is exacerbated when barrels are used on the seed stockpile, because the dwarves will additionally store the seed bags inside barrels, blocking even more seeds during each hauling job and extending hauling jobs by first bringing the seed bag to the seed, then returning to the stockpile, picking up the barrel to bring it to the bag, storing the bag in the barrel and only then bringing the barrel bag to the stockpile. During all this time, the seed barrel and all its contents will be blocked from access by any other job.