Current herb situation
ULTRA HIGH demand:
Nagrand Arrowbloom - used for Strength potions, Strength flasks and Stamina flasks
Talador Orchid - used for Intellect potions, Intellect flasks and Stamina flasks
Fireweed - used for Agility potions and Agility flasks
Medium demand:
Frostweed - used for Armor potions and is a minor component in all flasks
Starflower - used for Channeled Mana potions, Agility flasks and Intellect flasks
Low demand:
Gorgrond Flytrap - used for Mana potions and Strength flasks
We also need A LOT of Sorcerous Fire and Sorcerous Water.
Current production:
Fireweed - Silverfisk
Nagrand Arrowbloom - Silverfisk
Talador Orchid - Silverfisk
We need more people producing the high demand herbs.
To make your garrison only produce a certain herb you need a lvl 2 or higher herb garden and a follower with the Herbalism trait. Fiona has that trait and is available from a low level quest in south east Shadowmoon.