This Battle for Azeroth Herbalism leveling guide will show you the fastest way how to level your Bfa Herbalism from 1 to 175.
Herbalism goes well with Alchemy because you can use the herbs you pick and make potions. If you want to level Alchemy, check out my BfA Alchemy Leveling Guide.
Learning BfA Herbalism
The new BfA Herbalism skill is named differently for the two factions, but the name is the only difference between them.
[Kul Tiran Herbalism] is the Alliance version and [Zandalari Herbalism] is the Horde version.
Herbalism Trainers:
- Horde: You can find Jahden Fla in Dazar'alor at the Terrace of Crafters.
- Alliance: Declan Senal is in Boralus at the Tradewinds Market.
You can walk up to a guard in Dazar'alor or Boralus then ask where the Herbalism trainer is. Asking the guard will place a red marker on your map at the trainer's location.
How to speed up leveling
The Battle for Azeroth expansion introduces three new items that you can use to speed up farming herbs. You should use these if you can find them cheap at the Auction House, or craft it yourself if you can.
[Monel-Hardened Stirrups] - You can gather while mounted.
[Monel-Hardened Hoofplates] - Increase mount speed by 20%.
[Coarse Leather Barding] - Prevents you from being dazed. (mobs won't dismount you)
The one I would recommend the most is [Monel-Hardened Stirrups], which lets you gather herbs while mounted. Every mob scales to your level in Battle for Azeroth, so it will be hard to avoid the mobs attacking you while you try to farm herbs. If you have the 
[Sky Golem] mount, you can use that instead of the Monel-Hardened Stirrups
If your class has a tanking spec, you should switch to that while farming, so you won't get dazed and you don't have to use Coarse Leather Barding.
Don't forget to enchant your gloves with 
[Enchant Gloves - Zandalari Herbalism] or [Enchant Gloves - Kul Tiran Herbalism]! This enchant brings gathering time down from 1.5 seconds to 0.5 seconds. The lowered gathering time is crucial if you gather while mounted because mobs can still interrupt your casting.
Leveling BfA Herbalism (1-150)
The three zones below are where I think the most herbs are, but you can level in any other zone. Check out my farming guides for alternative routes:
Anchor Weed farming
Akunda's Bite farming
Winter's Kiss farming
Sea Stalk farming
Riverbud farming
Siren's Pollen farming
Star Moss farming
Dustvar - route 1
This route goes through an Alliance town so horde players might have some trouble here, but you can just run past the guards with mount, they shouldn't kill you.
Dustvar - route 2
Use this route if someone is already farming at the first route, or if you are having trouble going through the Alliance town.
Voldun
You can expect a lot of competition here.
150-175 in Nazjatar
You can still level in the old zones but the skill gains will slow down a lot at around 150 so I recommend switching to Nazjatar.
Don't forget to learn the rank 1 Zin'anthid from your trainer 
Rolm / 
Instructor Ulooaka at Nazjatar. (You have to finish the first few intro quest at Nazjatar before you can see these NPCs.)
I got the most Zin'anthid following this route. Bunch of mobs will be everywhere, so it's pretty bad to farm this herb until you get flying. Use the enchants I mention above or you will get dismounted every second.
I hope you liked this BfA Herbalism leveling guide, congratulations on reaching 175!