What are "weed" (the annoying plant) and "weed" (the drug) classified as that makes them treated differently grammar-wise?

Question

"Weed" (the annoying plant you don't want in your garden) and "weed" (the psychoactive drug) are treated differently grammatically. Just some example sentences

1. "There are weeds in my garden" vs "There is weed in my garden"
2. "There is a weed growing in this pot" vs "There is weed growing in this pot"
3. "How many weeds are growing there" vs "How much weed is growing there"
4. "I'm going to get rid of twice the weeds" vs "I'm going to get rid of twice the weed"
5. "Here are two types of weeds" vs "Here are two types of weed"

Basically, the two words are treated completely different grammatically. I was wondering how in particular the two words are categorized that links to their different treatment. (e.g. maybe one is a proper noun, and the other is not [I know that's not the case, but it's just an example of the kind of answer I'm looking for]). Or is this just some weird slang thing that only applies to the drug "weed"?

P.S.: I swear I'm not high while asking this question >.<. The impetus was actually because an anime brought up "happa", which could either mean "leaf" or "weed" in Japanese, and I wasn't sure which they were referring to. And then I got down this line of thinking >.<.

Answer 1

Weed - Marijuana - (chiefly uncountable) is what is known as a material noun. Its name is its definition.

Definition of Material Noun

The noun that gives the sense of a liquid/substance, that which is measured or weighed but not counted, from which various things are made, is called a material noun.

Material nouns are uncountable. They usually have an equivalent, but rarer, countable, common noun:

Uncountable: He was arrested in possession of 2 kilos of weed/marijuana.

Countable (rare): "Canadian and American weeds do not differ much in strength."

Compare

Uncountable: He was arrested in possession of 2 kilos of coffee.

Countable (somewhat rare): "Arabic and Robusta coffees do not differ much in strength."

As far as "weed - unwanted plant" is concerned, it is chiefly a common noun and thus countable:

"He has a garden full of weeds."

but is infrequently used as an uncountable noun.

"Weed in the crop will reduce the yield."