I'm going to play husband's advocate here, since it seems no one else has.
I'm not agreeing with him on any level, but the fact of the matter is I don't know either of you.
note: I'm sexist to both males and females.
It sounds to me like he's looking to get your attention, and to get things done quickly. These are both very common. He's probably trying to get you to spend less time in the garden and more time ~around~. That doesn't mean he's really trying to get you to spend time with him, but just so that all your time isn't taken by something else. The food thing, to me, sounds a bit strange. Everyone's angry about it, but the way you phrased it didn't sound like it was that bad. He said you both should get eating soon. You could have just as easily said yeah, sure, let's go out for burgers as to get angry about having to make him food. If you're feeling he expects you to cook, who's fault is that? We don't have people expect things of us if we haven't before made it clear we will it on a regular basis. I'm sure you take things he does for granted, as well.
Sounds like you need to talk to him, and not about the weeds. Do some stuff together, too. Plan to do some weeding together, side by side, without backseat driving from either of you.
Would I be upset if someone did this to me? Certainly. But I really do think that the garden is about the least important thing here, and both your feelings and his are at stake here.
I wouldn't suggest taking the chemical disposal into your own hands. That's the same passive aggressive behavior you're accusing him of and will just cause a war between you two. Tell him you don't want it used in the yard for a, b, and c reasons and you'd appreciate it if he got rid of it or gave it away or sold it or something. Maybe, if he is having memory issues, he will be able to remember an experience instead of a conversation.

note: I'm sexist to both males and females.
It sounds to me like he's looking to get your attention, and to get things done quickly. These are both very common. He's probably trying to get you to spend less time in the garden and more time ~around~. That doesn't mean he's really trying to get you to spend time with him, but just so that all your time isn't taken by something else. The food thing, to me, sounds a bit strange. Everyone's angry about it, but the way you phrased it didn't sound like it was that bad. He said you both should get eating soon. You could have just as easily said yeah, sure, let's go out for burgers as to get angry about having to make him food. If you're feeling he expects you to cook, who's fault is that? We don't have people expect things of us if we haven't before made it clear we will it on a regular basis. I'm sure you take things he does for granted, as well.
Sounds like you need to talk to him, and not about the weeds. Do some stuff together, too. Plan to do some weeding together, side by side, without backseat driving from either of you.
Would I be upset if someone did this to me? Certainly. But I really do think that the garden is about the least important thing here, and both your feelings and his are at stake here.
I wouldn't suggest taking the chemical disposal into your own hands. That's the same passive aggressive behavior you're accusing him of and will just cause a war between you two. Tell him you don't want it used in the yard for a, b, and c reasons and you'd appreciate it if he got rid of it or gave it away or sold it or something. Maybe, if he is having memory issues, he will be able to remember an experience instead of a conversation.