Harvest the plant that grows. You need to get 5 updates. You have to harvest them quick or they will die and disappear. You can do this entire quest sitting inside the Corrupted Druid Ring and just move around a bit. If the plant does not grow, pick up the seed and try planting it again. You have a better chance of the plant sprouting if you look for the "A Raven screeches at you from above" message before dropping the seed.