The crops take some time to appear after you get Level 2 of Harvesting, and they are cyclical after that. The only thing you can do is wait until the crops come in. If you have more than a dozen or so villagers, there won't be enough food on the farm to feed all of them, and the crops will be quickly depleted. It's a good idea to work toward Level 3 of Harvesting (fishing) as quickly as you can, so that food won't be an issue and you can grow your tribe and work on the puzzles.