I'm stuck trying to kill the tree in the greenhouse. I know I'm supposed to inject poison into the roots (s identified on the screen) but I'm getting killed each time I try and do that. Is that fighting action I'm supposed to use?

There's a video walkthrough for this part of the game here - would that help?

All those walkthroughs didn't help as they made everything look so easy.
I got some advice in the end on Steam that I needed to be pointing towards where the action was coming from (to the left) in order to be effective with my fighting.

I am glad to hear that someone helped you out.

sorry I missed this. Please feel free to PM me if you get stuck again.

I finished it a couple of weeks ago. I really enjoyed it. It actually got easier after the 'tree' bit.