As an agri-corps worker he would have been taught how to determine what was wrong with a particular plant, what it would require to be healthy.
As an apprentice to an exceptionally powerful master of the living Force he had learned how to commune on a deeper level; to know not only what it required but what it needed to grow, to thrive, even in adversity.
As a jedi Master he learned how to see the plant, both as an individual organism and in the context of the greater whole.
As a general in the grand army of the republic, he learned how to tell which ones were edible.
Obi-wan planted his feet solidly on the smooth stone of a rocky outcropping. Palms up and eyes closed, he opened himself up to the infinite ocean of power that was the Force, letting it cascade through him in an unending waterfall of light.
He lifts his hands slowly towards the harsh twin suns of Tatooine and, as if pulled into existence by the strength of his will alone, a tree sprouts from the bedrock in the middle of a barren, lifeless desert.
It occurs to him, distantly, that Darth Plagueis once claimed to have this power (though he is not sure who Darth Plagueis actually is; knowledge from the Force tends to be non-specific). But that doesn't really matter since, like what most of the things the Sith can do, it was a pale imitation of the real thing. And anyway, the sith's apprentice (Palpatine or Sideous or whatever he's calling himself now) killed him before he passed on the secret.
Obi-wan looks up at the tree. Bright green leaves dance and sway in the wake of the warm mid-afternoon breeze. He wonders, in the idle sort of way that a smart man with way too much time on his hands is prone to do, exactly who he is now.
He escaped the agri-corps by the skin of his teeth. He has long since accepted the death of his beloved Master and, more recently, the destruction of the jedi (though he will carry the weight of it to the end of his days). He is no longer a failed initiate, nor padawan, nor Master and Councilmember of the Jedi Order. He is not even a general, now that the Republic has been disbanded (and he is now, technically, a high priority fugitive from the central governing body of the galaxy).
He is beyond these things. It is as if all the lessons and sacrifices and hardships he has endured were stepping stones of understanding to a path that lead him here.
The rustle of the leaves above him whispers yes.
He stands an old hermit beneath a tree growing in the harshest of deserts and wryly thinks well, the will of the Force is nothing if not mysterious.