You have to kill purple flowers around the garden and then kill any mobs that spawn but, unlike normal, the flowers are not marked in any way and don't even have nameplates when you're attacking them.
Rant: whoever made this quest was an intern (or, if I'm being generous, an inexperienced new employee) who does not know how WoW quests are done! How does their manager / supervisor / team lead or whatever not catch stuff like this?
Come to think of it, a lot of the quests in Karesh have been poorly paced and overly grindy: quest mobs with low spawn rates to the extent that you're thinking it has to be bugged; or asking us to collect 12 energy pylons, one-by-one (fighting a gaggle of annoying little mobs each time), when 4 to 6 pylons would've done fine (and is more normal 'modern WoW' quest pacing). And there have been a few more that don't spring to mind immediately.
Review: for the above reasons, not enjoying general questing in Karesh so far, which is a shame as I think the zone is visually interesting and especially great for skyriding (especially since I found out that you can fly under the rock islands and pop up where you want: I was worried there might be fatigue or an insta-kill for going too far into the void but, no).
With the above caveats as the to pacing and grindiness of individual quests, I did quite enjoy the Campaign storyline. The Xal'atath / Alleria / player-character dynamic that Xal'atath is trying to set up is amusing and it was nice to meet Ven'ari again, although I was disappointed that she did not seem to remember us very well; there was no, 'Ah, Maw Walker it is good to see you again', kind of thing. Oh well.
Update (16 days later): turns out that I really didn't like Karesh. After spending that one full day there on my main, I haven't been back since. And I think I've bothered to unlock Reshii wraps on only one of my many alts. It was definitely not a conscious decision to do avoid the place, it just seems like this patch is just not at all engaging for me at the moment.