If it helps, this neediness and possessiveness appears to be a common symptom of the disease or at least the effect that having a disease that causes you to lose all control over your life would have on any 'normal' person. Just thought I'd make sure you were aware of that, in case you thought it was your wife who was just particularly frustrating, that it was just her personality causing her to be like this.
Dad used to constantly follow mum everywhere, and even when he could no longer get up and follow her, he'd follow her with his eyes. I think its partly to do with the fact that the dementia sufferer sees the primary carer as the one thing in life they can still control, they can make you cry, they can make you laugh, they can make you go angry...with you they have power. The other side of it is, that they know that you are the key to their survival, so of course they cling on like crazy. The final effect of this two sided coin, is that they can resent you or at least resent anything you do that may appear to suggest that they don't have control over you because common sense or instinct tells them that they are not safe if they can't maintain that control.
Doesn't make it any easier, and possibly you already have thought all this through yourself. Just thought I'd post it in case, you hadn't and because I know other people will read the post too, and it might help them at least come to terms with why the behaviour is occurring at least.
But as I said, doesn't make it any easier does it?
Best wishes with your gardening.