Crimson Nirnroots, unlike normal Nirnroots, are only found in Blackreach near the giant glowing fungi. Crimson Nirnroots still make the sound of chimes when the Dragonborn is nearby and have a white/yellow glow that is distinguishable from the blue glow of the surrounding fungi. Going into audio settings and turning the music down will make the chime sound easier to hear.
There are at least 44 Crimson Nirnroots in Blackreach, so it is not necessary to find them all.
While they can be found anywhere on land, Crimson Nirnoots are still found more commonly near water. One is in the central pool of the Derelict Pumphouse, while another is found far from water, high up where the Frost Troll lives.
Crimson Nirnroots will respawn after 10 days. Harvesting respawned Nirnroots will still count toward the quest counter.
To place a Crimson Nirnroot near the player, type player.placeatme 000b6fb9 in the console.
The quest tracker may not tally all collected Nirnroots properly. This occurs because only one Nirnroot is initially needed, but if more are collected before seeing Avrusa, the others are counted as quest items also.
The above bug can help the player receive the Hero of the People Achievement, which is to complete 50 Misc. Quests, by storing and retrieving the quest-item Nirnroots from a chest repeatedly.
Collecting Crimson Nirnroots after beginning Avrusa Sarethi's quest may cause the journal's counter to subtract, instead of add, acquired plants.
The quest will not reduce the Dragonborn's Crimson Nirnroot count if any are eaten or used in Alchemy. Once the count reaches 30, it will direct them to Avrusa Sarethi, but she will not accept the Nirnroots unless the Dragonborn actually has 30 of them in their inventory.
Any Crimson Nirnroots collected before finding Sinderion's Journal may not be counted by the quest tracker. Dropping uncounted Nirnroots one by one will reduce the quest counter, and picking them up will increase it. To fix this, put all uncounted Nirnroots in a container at once as a single stack, then withdraw them individually.
PS3 If the Dragonborn collects more than 30 Crimson Nirnroots and deposits the extras in a container before visiting Avrusa Sarethi, the quest may say "Collect Crimson Nirnroot in Blackreach 30/30", indicating that there are in fact 30 Crimson Nirnroots in the player's inventory, but the prompt to see Avrusa Sarethi (and the map marker) is absent. Simply taking another Crimson Nirnroot from the container should fix the problem. (PS3 after 1st update).
Speaking to Avrusa about Sinderion's dead body before showing her the Nirnroot may prevent her from engaging in further conversation with the Dragonborn, rendering the quest incompletable. (Fixed on PS3, tested).
360 PS3 When Crimson Nirnroots are stored in containers or dropped, the game may subtract more from the quest counter than were actually lost. Storing or dropping individually does not fix the problem.
PS3 Sometimes, the quest counter will say that 30 Crimson Ninroots have been collected when the actual count is lower, and the quest will become incompletable. The only way to resolve this is to reload an earlier save.