Use an Evergreen Pouch with a Packet of Tharlendis Seeds and two Un'Goro Soil samples to try and cultivate samples of Morrowgrain. Bring 10 Morrowgrain to Mathrengyl Bearwalker in Darnassus.
Here's your Evergreen Pouch that you'll need to use the Tharlendis seeds with. You also need to have Un'Goro soil samples on hand to use as fertilizer for the seeds. Just use the pouch when you have everything; the pouch will take care of the rest.
When you have enough morrowgrain, bring them here to me in the enclave. Please don't bother the Arch Druid; he's a very busy man, and he doesn't need to be disturbed every time someone returns with another batch of morrowgrain!