Green’s Dictionary of Slang

parsley n.

1. the female pubic hair [? resemblance].

[US]Maledicta IV:2 (Winter) 187: To [...] return to the quim whiskers, common terms include [...] the botanical (Furzebush, forest, bush and parsley).

2. nonsense, rubbish [? the insignificance of the herb].

[US]Ade Forty Modern Fables 83: He knew the kind of Conversational Parsley that is needed to Garnish a full-blown Intellectual Vacuum.
[UK]E. Pugh Cockney At Home 164: All that about the ole woman an’ so on is jest parsley. There ain’t no ole woman.

3. (US black) money [it is green].

[US]R. Goffin Horn of Plenty 104: Las’ year I was makin’ a buck a day. Now I’m doin’ twice as good, an’ that’s my limit’ [...] ‘You need some parsley—ain’t that right?’.

4. in drug uses.

(a) phencyclidine [the use of parsley as a base for smoking phencyclidine].

[US]H. Feldman et al. Angel Dust 124: The large number of street names it has been accorded over the years: [...] parsley.
[US]ONDCP Street Terms 16: Parsley — [...] PCP.

(b) marijuana.

[US]ONDCP Street Terms 16: Parsley — Marijuana.

In phrases

take a turn among the parsley (v.)

to have sexual intercourse.

[US]Maledicta IV:2 (Winter) 197: The terms used for copulating […] are not really euphemistic because it is implicit that no ambiguity could possibly result and, unlike euphemisms, they are, or used to be, avoided in polite, mixed company. Related to this group are the allusive […] to take a turn among the cabbages [...] among the parsley.