Garlic seeds are seeds used to grow garlic crops. They were added in the Sun and Moon update. When harvested, it will revert back to the seed form. It can be crafted with 8 garlic near a fire source. It will dissapear after 8 days (64 minutes) if not damaged by other means. Garlic seeds will dry up after a period of time. When dried, garlic seeds cannot support garlic crops anymore. Player needs to water it with a watering can so it won't dry up. Humans in vampire mode start out with 3 garlic seeds in their inventory. Vampires are allergic to garlics, and start to lose their health when they are near it or have it in their inventory. Eating them as a vampire will immediately kill them. The death message will display: You ate garlic as a vampire, what did you expect?
You can find these around the forest! But keep in mind there ain't only garlic seeds dropped there. (Except berry seeds)