We have begun migration of most wikis to our new host, Amazon Web Services. All but the top 100 wikis are in read-only mode until the migration is complete. Estimated completion: TBD -- Update: Fri 10/20 11pm UTC - We have encountered some unexpected issues. Our staff is working around the clock to complete this process as quickly as possible. Thank you for your patience.
From Terraria Wiki
Crimson Seeds are a type of seeds which can be planted on Dirt Blocks. If done so, they will spread the Crimson in all directions through Crimson grass. They can only be obtained in a Crimson world, either as a drop from the Eye of Cthulhu or purchased from the Dryad for 5 each, during a Blood Moon in a Crimson world.
- Crimson grass may also be obtained by planting regular grass and using Red Solution on it.