Horizon Forbidden West is filled with resources and materials for you to sell and craft throughout your journey in the forbidden west. These materials all have their uses—some will allow you to craft arrows, traps, or other useful items like the fast travel packs. Horizon Forbidden West also adds new resources, like the dye plants.
Verdant Bloom is a dye plant used for unlocking dyes at Dyers. You will need to play many hours before coming across your first dyer, which can be found at Plainsong. The Dyer will only become available after completing the quest The Sea Of Sands. In order to dye your outfits, you will need to supply the dye plants and they will spruce up Aloy's outfits for you.
Where do you find Verdant Bloom?
Verdant Bloom is an uncommon dye plant and is harvested from the Verdant Bloom plant. This plant is often found growing on rocky cliffs. Check the edge of cliffs and other rocky areas. It's worth noting that this plant appears as red in the inventory, however, it is green in the open world. Your focus pulse is useful here to find Verdant Blooms, as well as highlight climbable cliffs used to reach the rocky places where you can find them.
For more on Horizon Forbidden West guides, check out How to cook food in Horizon Forbidden West, and is it worth it? and What is Azure Bloom used for in Horizon Forbidden West?