Email them and tell them you're unhappy with your user experience. Their algorithm is incredibly powerful, but as most things technological, is far from fool proof. They're a reasonable company and are actually a leading factor in UX development at this point in time, so you might be able to rectify some kind of change through simply emailing them.
The problem isn't even with their algorithm, it's the fact that weed is thrown around so easily as a synonym for cannabis. It's not google's fault that stoners call it weed and their web crawlers categorize cannabis in the same arena as unwanted plants (though cannabis is considered an unwanted plant to many). It being bold simply means it's a commonly searched for term. To avoid confusion during search results, refine your queries and perhaps use the plural "weeds" instead. For instance:
Unrefined search: "How to I eradicate a weed in my yard?"
Refined search: "kill weeds <insert locale>"
The first will probably show you 100,000 results including a ton of how to's for making pipes, bongs and awesome grass pics. The second will potentially lead to 50,000 results more specifically discussing weed killers, herbicides and organic methods of weed control. It's all in the context and construction of your query.
