First off, a profession can only be leveled up to whatever your character level is multiplied by ten. For example, if your character is level 9, you can only level up your herbalism up to level 90. Secondly, I took an extremely long time to get past level 1 herbalism, when in reality the Violet plants were right next to me.
As soon as you talk to the Herbalism trainer (Who is in the top floor of Yasker's Tower, which is in the very center of Nezebgrad) the Violet plants are all around that room, as well as in the hallway nearby. You must buy the Herbalism book from the Herbalism trainer to learn the profession, and buy the Rusty Sickle from the Herbalism Trainer, in order to start collecting these herbs. You can easily spot the Violet Herbs, by the little green Nodes floating around the plant. I missed this and many people in the channels still continue to ask where to find these plants. Answer: Right next to the Herbalism trainer!
I stayed here collecting Violets until I reached level 30 in Herbalism. I'm sure you can level your skill up higher here, but I only went up to level 30 before I went on to the next quest. The first Herbalism quest you are given only requires that you collect 10 Violets anyway. You can get your Herbalism skill up to level 65 by collecting Violets here, though it may take a while.
Once you turn this quest in, you can then get the next quest called, The Basics of Herbalism: The Second Step. This quest requires you to bring 13 Carnations and 13 Dandelions to Nadine de Grandeur. To complete this quest, you must go to Old Square and collect 13 of each of these flowers. I marked the area on the map below, with two yellow dots. There are a good amount of nodes here, so it won't take a long time to complete this quest.
Once you have collected the quest items turn the quest in and you can get the third Herbalism quest called The Basics of Herbalism: The Third Step. For this quest you are required to bring 13 Lilies of the Valleys and 13 Sorrels to Pebbles the Rowdy. Pebbles the Rowdy and the quest items can be found by the three yellow dots on the map below. To get there, you can go out by where is says To Severny Steppe and then go west, or go out by where it says Arena and go north.
Once you get to this area, you can keep collecting herbs until you get to level 131. It went pretty quickly up until about level 120, but then slowed down considerably from 121-131. After that I did not get any more skill-ups from this area. I then went around Nezebgrad for literally four hours (without a mount) collecting herbs and finally I reached level 140.
I put dots of various colors on the Nezebgrad map above, illustrating the different levels of herbs I found in each area. These colors depict as follows: White Dots= Common Herbs, Green Dots= Uncommon Herbs, Blue Dots= Rare Herbs and Purple Dots= Epic Herbs. Unfortunately I cannot prove whether or not a higher grade herb makes you skill-up faster than a lower grade one.
From level 131-140 I ran around Nezebgrad collecting these herbs, but there was no pattern that I found (e.g. 20 herbs collected= one skill-up). Instead I found the leveling was much more random. As an example, I collected 5 herbs and I leveled from 135-137 within this time. On the other hand, I had to collect 10 herbs just to get from 133-134.
The good news is that once you finally reach level 140 in Herbalism, it is smooth sailing from there. You can go to Igsh Military District where the minimum level to collect herbs in 140. You should level from 140-150 just by collecting about 15 herbs from this area. Everywhere you go to level-up your character from here on out, will have herbs that will quickly increase your Herbalism skill.
Make sure at levels 20, 30 and 40 you remember to buy the next level sickle in order to harvest higher level herbs. Also, if you have enough bag space, be sure to save your green (uncommon), blue (rare) and purple (epic) herbs. You will find Alchemists later on who will pay you for your herbs that have certain agents (e.g. Healing Agent, Strengthening Agent).
Well that's all from me, if you are stuck between levels 131-140, keep collecting herbs in Nezebgrad (All except the Quest items) and you will eventually reach 140. It definitely can get aggravating, especially if you don't have a lot of patience, but if you keep at it you will definitely get to 140. Good luck to all of you, I hope my guide has helped!
If you have any questions, feel free to comment on this post.