The reason it is repeatable is because if your not a NE then you can do this quest over and over and over and over and over and over (you get the idea) again to get exalted status with Darnassus so you can get a sabre. There ya go!

You can also hand in morrowgrain to this quest in Feralas , http://classicdb.ch/?quest=3792 , if you are lucky enough to generate 20+ morrowgrain

The cache is completely random. Just give to guild friends or others what you do not use. Many times has a friend been in need of mana and that unused Moonberry Juice comes in handy.

The reason it is repeatable is because if your not a NE then you can do this quest over and over and over and over and over and over (you get the idea) again to get exalted status with Darnassus so you can get a sabre. There ya go!

This information should be accurate as of patch 1.11.2

Morrowgrain quests:

The Morrowgrain quests can be quite involved as there are two quest givers and turn-in locations. Also the rewards given are different for both turn-in locations. The actual process to get Morrowgrain takes several steps as well.

The quest line starts with a quest called Morrowgrain Research which is given out by Arch Druid Fandral Staghelm. Arch Druid Fandral Staghelm may be found at Anonymous coordinates 35,8 in Darnassas. He is located at the top level of the Druid complex (Cenarion Enclave). He asks you to take a packet of 20 Tharlendris seeds to the middle level of the same complex and give them to Mathrengyl Bearwalker who gives out the next quest. That quest is also titled Morrowgrain Research (Just to confuse things).

The second Morrowgrain Research quest has you take a special pouch called an Evergreen Pouch (Provided when you receive the quest) and put into it 2 Un'Goro Soil (Collected in Un’Goro Crater) and 1 of the Tharlendris seeds from the packet (First 10 seeds given to you with the quest). With 2 Un'Goro Soil in your backpack along with 1 Tharlendris seed, you right click the Evergreen pouch. The pouch will plant the seed into the soil and grow an Evergreen Herb Casing. When you right click the casing, out will pop a random herb. One of the herbs grown may be Morrowgrain. When you have 10 of them you turn them in to complete the quest. You can repeat this quest as many times as desired. You can grow a new Evergreen Herb Casing once every 10 minutes.

There is a second parallel quest line involving Morrowgrain as well. This chain of quests starts with either Innkeeper Shyria in the Inn of Feathermoon Stronghold in Feralas or with Tannysa the Herbalism trainer in the Mage Quarter of Stormwind. Talking to either of these two people will give you a quest titled Jonespyre's Request which asks you to go talk to Quintis Jonespyre in the Feathermoon Stronghold in Feralas. Quintis Jonespyre will then give you the repeatable quest titled The Mystery of Morrowgrain. This quest is identical to the above quest (Use the Evergreen pouch to grow an Evergreen Herb Casing from 1 Tharlendris seed and 2 Un'Goro Soil and out pops a random herb) except you only need to turn in 5 Morrowgrain.

In the end, you now have two locations to turn in Morrowgrain:

Turning in 5 Morrowgrain to Quintis Jonespyre in the Feathermoon Stronghold in Feralas will give you 25 reputation with Darnassas. In addition he also gives you another packet of 10 Tharlendris seeds so you can go out and grow more.

Turning in 10 Morrowgrain to Mathrengyl Bearwalker at the Cenarion Enclave in Darnassas will earn you 50 reputation with Darnassas. In addition he also gives you a Cenarion Circle Cache. Opening this will provide a random number of items as loot. Typically there are 4-8 items in the bag although I have seen only 1 before and as many as 14 per Cenarion Circle Cache. The Cenarion Circle Cache typically contains food, drinks, scrolls, potions, herbs etc. For a list of the types of items found in each Cache please see the following link: https://classicdb.ch/item=5533 You can get a lot of really good stuff in these caches.

Where to get Un’Goro Soil: Un’Goro Soil is found in Un’Goro Crater (Southern end of Kalimdor). Un’Goro Soil is dropped (from Dinosaurs) throughout the crater. Just run around the zone (Avoiding being stepped on or eaten by the dinosaurs) and right click the dirt piles you see laying on the ground. Un’Goro Soil is often found in the AH as well. Un’Goro Soil stacks up to 100 units per stack now.

Where to get Tharlendris seeds: Tharlendris seeds may be purchased from either of the two turn-in NPCs or you can get them as part of your turn-in reward when you turn in Morrowgrain to Quintis Jonespyre in the Feathermoon Stronghold in Feralas.

Where to get an Evergreen pouch: An Evergreen pouch is given to you when you receive the second Morrowgrain Research quest. Replacements may be purchased (For around 1 Gold) from either of the two turn-in NPCs.

The rewards:

Once you have grown Evergreen Herb Casings and retrieved the herbs out of the casings you can either turn in the Morrowgrain for reputation, sell it on the AH or use it to make Cenarion Herb Bags (Manufacturing 20 slot herb bags requires 8 Morrowgrain as one of the materials to make 1 bag). In addition the loot from the Cenarion Circle Cache is typically valued at several gold and may be used or sold as needed.

In addition to growing Morrowgrain, the Evergreen Herb Casings often contains other herbs which may be used or sold as needed. How much Morrowgrain or other herbs you grow and which types depend on your Herbalism skill. As an example, I dropped the Herbalism profession completely and grew 65 Evergreen Herb Casings. Out of those casings I received the following:

Morrowgrain 50
Kingsblood 6
Gromsblood 3
Earthroot 9
Briarthorn 8
Liferoot 7
Mageroyal 5
Sungrass 2

For a total of 90 herbs averaging 1.48 herbs per Evergreen Herb Casing. For the most part these are lower-end herbs.

I relearned Herbalism and worked it up to 300 skill level. I then grew 65 more Evergreen Herb Casings. This is what I received from those:

Morrowgrain 75
Kingsblood 22
Gromsblood 2
Liferoot 6
Sungrass 5
Stranglekelp 13
Blindweed 5
Goldthorn 22
Firebloom 2

For a total of 152 herbs averaging 2.34 herbs per Evergreen Herb Casing. For the most part these are higher-end herbs. The maximum # of herbs out of any single casing is 5.

As I went up in skill level, the numbers and types of herbs increased steadily.

All in all 300 Herbalism will result in a 50% increase in Morrowgrain output and a 70% increase in the number of herbs grown as well as large increase in the value of the herbs.

Most people performing the Morrowgrain quests keep the pouch, seeds and soil in their backpack and as they run around Azeroth they pop out a new batch of herbs once every ten minutes. For an Alchemist this results in a steady supply of herbs for use in potions and for others it results in a steady supply of cash from the sale of those herbs. The hardest part is having enough space in your bags for all those herbs!

As an alchemist I would recommend taking your morrowgrain to Feathermoon in stead. You get 10 seeds for turning in 5 morrowgrain. You'll gain 16 rep points apparently and even if you do not intend to use the seeds, they sell pretty well.
Ok, collecting the soil is tedious work but while in Un'Goro one can pick up herbs for Major Healing potions as well.

Feathermoon quest:

Here is the link of my post.

(Quest #3791)

And save yourself some time and trouble. Herbalism bumps the chance and # of morrowgrain you'll get out of these things. My 310 Herbalist (with gloves and enchant) averages 5-7 morrowgrain per package. I only my other toons when I want to get Grom's Blood or some other high level herbs.