In-game description: Your studies of herbology help you to spot and collect useful and precious ingredients, whilst enjoying really nice and sunny quests.
In-game effect description: Advancing this skill increases chance and amount of herbs found in quests.
The higher the level of Harvest, the more herbs can be found. Certain herbs can also only be found as soon as the player has a minimum skill level of Harvest. Ingredients for bottles for example can only be found with level 7 Harvest skill.
Herbs are separated into 4 tiers: Tier 1 herbs can be found with level 1 Harvest skill, Tier 2 with level 2 Harvest skill, Tier 3 with level 7 Harvest skill, and Tier 4 with level 12 Harvest skill.
Vial of Nature increases Harvest level by 1, allowing non-alchemists to find Tier 1 herbs, or level 30 alchemists to find Tier 3 herbs.
Potion of Nature increases Harvest level by 3, allowing non-alchemists to find Tier 3 herbs, level 26 alchemists to find Tier 3 herbs, or level 24 alchemists to find Tier 2 herbs.
Bottle of Nature increases Harvest level by 5.
VPB gives 9 Harvest, which means that alchemists with 3 Harvest can get 4 Tier herbs.
While Ephijora, an ingredient for vials/potions of nature, is a Tier 1 herb and can be found by all alchemists, or by anyone with a vial of nature, it is still a fairly rare drop. This makes vials of nature somewhat pricey, and potions of nature very pricey.
In theory, vials are self-sustaining: questing during any time that isn't Night with a vial of nature yields at least 1 Ephijora.