Turnip seeds are found in the swamps. They aren't as common as carrot seeds but the flower is a nice bright yellow in the gray and black swamp so they aren't hard to see though you may have trouble finding the plant. When you get the seeds it opens the turnip plant in your recipes. Then plant the turnip seeds in your garden and when you harvest the 3 turnips you unlock the seed turnip recipe. Turn your 3 turnips into seeds, harvest and plant again, then use 3 of the turnips to make the spice rack and plant the rest of the turnips for seeds.