[Updated on September 4, 2024, to revise outdated formatting and improve readability.]
There are quest prerequisites that you must fulfill before accepting Uma’s Garden in Zelda Tears of the Kingdom. After completing the Hateno Village storyline, you must go to the local school and help the teacher tell the children about the history of Hyrule. To do this, you must complete Teach Me a Lesson 1 and Teach Me a Lesson 2.
After completing this requirement, the teacher will thank you for your help and allow you to use the school field to grow various foods. Get out of the school and go down to the lower clearing. Near a small piece of land, you will meet NPC Uma, and after talking to her, you will accept Uma’s Garden side quest.
An elderly but energetic woman will tell you a little about farming and offer to plant some seedlings. You only need to select the appropriate fruit/berry/wheat/vegetable from your inventory. The list of products available for cultivation is vast, so choose what you most often use for the recipes. And once you select a product, Uma gets to work.
After that, you can leave to do other things. There is no way you can complete this quest instantly. You must wait for two in-game days, or about an hour of real-time, after which the harvest is ripe. At the same time, skipping campfire time or other ways to speed up time will not affect the growth rate of plants in your field. One way or another, you will have to wait about an hour in real-time.
After an hour, return to the field and talk to Uma again. She will say that your harvest is ripe, and you can harvest it. After that, you will complete the quest and be able to use the field permanently. You can collect about ten units of planted product from each harvest. And once you’ve harvested, talk to Uma and ask her to grow something else by choosing from the list in your inventory.