Bison grass is an alchemy ingredient in The Witcher 3: Wild Hunt that is needed to craft the following items:

Unlike most herbs, it can't be found growing anywhere in the game, and is extremely rare as random loot, making it almost certain that some has to be bought in order to obtain all the necessary doses. It can be purchased from the following merchants:

• Tomira in White Orchard
• Herbalist in a shop in Glory Lane
• Merchant in the Fish Market in Novigrad
• Otto Bamber at the Herbalist's Hut northeast of Oxenfurt
• Herbalist in Kaer Trolde Harbor
• All herbalists in Toussaint, except Pinastri

Trivia

• In real life, bison grass is what gives Żubrówka vodka its distinctive flavor.