harry potter - Why did Hermione smell grass in the Amortentia?

In the chapter introducing Amortentia it's pointed out that each individual smells something different depending on what they're attracted by.

"And the steam rising in characteristic spirals," said Hermione enthusiastically, "and it's supposed to smell differently to each of us, according to what attracts us, and I can smell freshly mown grass and new parchment and -"
_{(Half-Blood Prince, Chapter 9, The Half-Blood Prince)}

We know from JKR that Hermione smelt Ron's hair in the potion, though she wasn't prepared to admit it openly at the time.

Jess Mac: What was the third smell that Hermione smelt in the Amortentia potion in Half-Blood Prince (i.e. the particular essence of Ron)?

J.K. Rowling: I think it was his hair. Every individual has very distinctive-smelling hair, don't you find?

It makes sense in the scheme of things that she is attracted to something of Ron's. I also understand why parchment would attract her since she's a huge bookworm. But why the grass? Is there any indication about why freshly mown grass would inflame her passions?

Answer

We don't know.

There doesn't seem to be any other canonical indication of a special connection between Hermione and grass; it's not something explored elsewhere in the books or expanded on by JKR in interviews.

I did find this fanfic which gives some plausible (but of course not canonical) explanations of why grass means so much to her: the grass of Hogwarts grounds associated with happy memories, and also the grass of her parents' lawn at home reminding her of her childhood.

Note that, as others have pointed out in comments, the fact that she smelled grass in the Amortentia potion doesn't necessarily mean it "would inflame her passions", just that it's a smell she loves and which perhaps has some special (not necessarily romantic) meaning to her.