To unlock this feature you will have to position yourself at reputation level 3 in Inazuma> this will allow you to obtain an item called Naku Weed from an NPC named Madarame Hyakubei.
When you manage to get hold of the Naku Weed, a new world mission called "Art of Horticulture" will be activated, allowing you to unlock the gardening system within its Serenitea Pot after completing it.
With the seed dispensary you can collect and plant seeds, and you can achieve this by completing the world mission "Art of Horticulture", which you can access with Madarame Hyakubei's Naku Weed by positioning yourself at reputation level 3 of Inazuma.
That's all you need to know about how to unlock gardening and seed dispensary in Genshin Impact and now that you know, we hope you can get the most out of these two features and everything new that update 2.0 has for you.