Because I feel it needs to be known to anyone who might be interested here I will try my best to explain Elsu's abilities.

First off let it be known that he does NOT control the plants. He can force his will upon them, yes, but he does not control them.
His magic, which effects only plants, constantly seeps out of him and is absorbed by the plants within so many miles of him. This gives them sentient life, with it they can mentally speak and think as well as physically act according to their own will.
The plants become sentient beings. Capable if thought, emotion, movement, etc.
the only thing they can't do is things like actually speaking, because they don't have a physical mouth to do so. Instead they communicate by telepathy.

So it's not Elsu's doing if a plant randomly grabs someone or does something with him near, it's the plant acting on its own.
The way to tell if it is Elsu's doing is if his eyes are glowing, because he must use concentration and more magic to be able to force his will upon the plant. 

And yes, they can still move and such even if he is unconscious. The only way to avoid any of this happening is to redirect the path of Elsu's free-flowing magic. That is to allow something, or someone, to absorb the magic that flows out of him instead of the plants. If this isn't happening they will continue to absorb his magic and do as they please.

The way Elsu stops, or slows down or attempts to stop, this from happening is to consciously keep his magic from flowing out of himself. This takes concentration and effort. It is also bad for his health as he will get a magic build up and could either get sick, injured, or have it all burst out randomly.
Though having too much leave him at once can do just as much damage...

If anything here doesn't make sense or you would like further explanation please let me know and I will try to the best of my ability.