Tuck knows only the most general information about the thickets of Old City (since his checks are untrained). These overgrown areas usually sit against an inner or outer walls of the district and are full of dense brush, old trees, and creeping vines. The Guild of Roots is responsible for keeping the thickets from spreading but the guild rarely delves deep into the thickets. The members just cut away the growth at the edges and sell the castoff to stables as feed for horses.
(The Guild of Roots is not responsible for the plants in the Gardens. That falls under the sway of the Tenders of the Ascetic's Temple.)
Tuck doesn't know anything specific about the Jade Thicket, but he knows some of the members of the Guild of Roots (see below). They would know more about Old City's thickets (and the other district's thickets too [except the ones in Wizard District]).
Knowledge Beyond Your Check:
There are
three kobolds in the guild that Tuck has heard of: Azszi Greenblood [female around Tuck's age], Sceggon [male], and Xozzin Moonbone [very old male].) He's never met any of them but knows Xozzin is semiretired and
very respected among the kobolds of Bluffside. Azszi is the daughter of an old rival of his uncle, Zenk. Tuck knows nothing about Sceggon other than his name.