Ideas for farming?

So I have an idea for a game that may involve the player planting some plants of the terrain, then harvesting and selling the harvested plants. However I am struggling with creating a system of actually planting the plants on a 3d terrain. I only want the player to be able to plant crops on "farmable land", so maybe I could make a trigger where in which the player can plant? And how to get it to instantiate a plant on the ground, using raycasts? Idk, I'm curious to hear your guys ideas.