For those playing on Xbox and you are trying to feed the freshly planted seedling 'baby' whatever its tending 'craving item' is:

Face the seedling, hold down the Y button to access a radial dial and then at the top of the radial is the item it wants to be fed. As long as you have it in your inventory, click on the item to feed it, and it'll remove it from your inventory.

When I looked at the seedling, it showed what it wanted to be fed, but it did not say what button to press to feed it, which is dumb. I couldn't find this info anywhere, and discovered this in a last minute panic trying to feed it.