For those of you slightly frustrated by the lack of this deadly ingredient in-game...

Adds a small satchel to the exterior of the Dawnstar Dark Brotherhood sanctuary, containing
3 Jarrin Root, and a more potent modified version.
The modified version doesn't use scripts or anything, it simply deals 250 damage every second for a minute, ensuring a nice, inevitable death.
(The default Root deals a single dose of 200 damage.)
Of course the modified version isn't that necessary, I just felt cheated that I wasn't killed outright by the default version (R.I.P. Poisoned Apple T_T)
The satchel respawns like any other loot container, so there'll be a steady supply.

The stash is located just by the rock and tree slightly north of the Sanctuary door - See pics.

Alternate high quantity (100 Root) version for those of you who couldn't give a flying fig for realism.

Install:

Extract DBJarrinRoot.esp to your Skyrim/Data folder, or you can use DBJarrinRoot HighQ.esp instead.
Then select your chosen .esp in the Data Files section of Skyrim's launcher.

NMM: Will work with NMM but will not correctly extract the optional .esp, to use that simply find the DBJarrinRoot folder and manually place it in /data.