Time is your friend as well as doing the full quest line after you get the plant pot in your home. Once the item is not tagged house lore, wait 23 hours (or is it 24) and will be able to harvest a rare.
23 hours per quest for the seedling. 23 hours per harvest once you have the garden version. http://eq2.eqtraders.com/articles/article_page.php?article=q249&menustr=060000000000
So I have begun to wonder about these little gems now. The Goblin would harvest all tiers and bring back rares on occasion but our lovely new plant only brings back 1 tier, 1 item per day. I am curious to see how it may be evolved to maintain it's relevance and value in comparison over time.
Yeah, it's not quite the rare factory that a lot of folks think it is. Even with a full stable of plants going, you get one rare every 23 hours, and it's a chance at one of *six* different rares, with varying chances for each. It's awesome, don't get me wrong, but it's still going to take time before there is a steady supply of the rares. (Especially since the harvesting nodes only spawn in the first instance of Obulus Frontier right now, further constricting the supply.)
As more people get and use these plants the prices are going to go down on the new rares, which is a good thing (even though thanks to the new rares I now have more plat than I have ever had at one time in the game).
Many of us have ponies who also get rares (and can get holiday harvests in season). The new rares are EXTREMELY rare. Having a steady, if slow, supply of rares is a very nice boost. Plus, during the quest to turn the goblin in, you get bits for a 64 slot pack. Additionally, the summon goblin buff turns into a harvesting boost that reduces the base harvesting time to 1.5 seconds.. then you add the decreasers from your harvesting tools...
