This one took me a bit but mainly because how long it takes to walk around Blackreach. You have to be methodic with the area you cover even though it's rather hard to break up Blackreach into sections. Make sure you check some of the small ruins behind doors that are inside Blackreach itself. The trickiest spots in my opinion was one that was in a room with water and you had to swim to unlock an underwater door blocking it. There's also a large body of water near the perimeter of Blackreach that I had to swim around in to reach one that isn't near any kind of path like most of the others. Wouldn't sweat over it though, It's not critical to the main quest and it just gives you a permanent active effect after completing the quest:Anyone else having trouble finding those last crimson ninroots in Blackreach? I have 26 of the little bastards and can't find the last four for the life of me. I could be sprawling the wintery countryside punching dragons in the face but instead I'm spending way too much time underground collecting flowers.
"A 25% chance of creating a duplicate potion when using your alchemy skill." So yeah, not that great unless you like alchemy.