The spirit seeds are found in spirits island and it only takes less than three minutes to crop. This guide will let you know how you can get the spirit seeds in Roblox Islands.
In order to get spirit seeds, you will need to make your way to the spirit island. Start a conversation with Ctherine, she will ask you to capture the spirits on the island to get a reward.
After that, you will need to roam around the island to capture the spirits, then go back to Catherine and she will give you the spirit seed.