Entering Tel Mithryn Apothecary, Elynea Mothren can be heard yelling: "Damn that man! He is being totally unreasonable. I don't care if he's a Master Wizard. He can't treat me like this!" Asking her what happened, she reveals Neloth's tower is withering and needs to be repaired:
Master Neloth? What did he do?: "That fetcher told me to fix his house. If I don't, he'll find a new mycologist who will. Decades of loyal service, and he'd just throw me out like yesterday's breakfast!"
What do you need to fix the tower?: "Three taproots soaked in the headwaters of the Harstrad river. I'm an old woman. I can't possibly make that trip. It's way too dangerous. If you get some taproots, I'll pay you to dip them in the headwaters and bring them to me."
She can be questioned further about the issues, which reveals where some taproots can be found:
Where can I get taproot?: "Where do you think? You have to cut it out of a Spriggan. Although sometimes you can buy them from alchemists."
What can you tell me about the Harstrad headwaters?: "It's special to the Spriggans. They seem to like to gather there. Something about the waters attracts them. There are bound to be some there, so be careful."
As mentioned, taproot can be either bought from an alchemist or obtained from the corpses of spriggans. The unmarked Giant Nirnroot Island is a convenient location to obtain taproot as it is home to three leveled spriggans.
Once they have been obtained, proceed to the Headwaters of Harstrad. Another spriggan lives in this small cave, but once it has been killed activate the headwaters to soak the taproot. Once this has been done, return to Elynea. She will keep two of the Soaked Taproot and request that the other be planted in the withered interior wall of Tel Mithryn.
Travel up the tower and plant the Taproot into the large dark bulge on the wall. Return to Elynea, who replies "Good. Now maybe Neloth will get off my back about it." and grants a reward. This completes the quest.
Elynea rewards the Dragonborn with two leveled Potions of Well-Being. These potions restore a certain amount of Health, Magicka and Stamina. The potency of potion that is received is based on character level.
| Part of the Telvanni tower at Tel Mithryn is withered. Elynea needs three taproots soaked in the headwaters of the Harstrad river to repair it.
|Part of the Telvanni tower at Tel Mithryn is withered. Elynea needs three taproots soaked in the headwaters of the Harstrad river to repair it. Elynea kept two taproots for herself and told me to plant the last one in the withered part of the tower wall.
|I helped Elynea repair the withered tower of Tel Mithryn by planting taproots in the wall that had been soaked in the headwaters of Harstrad river.
- It is later revealed in Ildari's Journal, vol. III that Ildari Sarothril, Neloth's former apprentice, was responsible for withering the tower.