Garlic mustard - a winter edible. The roots of garlic mustard are best gathered when the plants are dormant (in the colder whether), when they are at their most flavorful. They can be used in cooked dishes such as stir fries or stews, but they are probably better used as a condiment. They have a flavor similar to horseradish, though somewhat milder. I have often ground them up in vinegar, with a little sugar added as a substitute for horseradish sauce. However, one of the best ways to use and preserve the roots is to dry them out and grind them into a spicy powder that can be sprinkled on food or used as a flavoring in cooking.