Hairy Vetch Cover Crop Seeds - OrganicCertified Organic. Hairy Vetch is a legume that is widely used by growers in the United States as a winter cover crop, as it is both winter hardy and can fix as much as 200 lb acre of atmospheric nitrogen. Gardeners often plant Hairy Vetch seeds as a cover crop (a nitrogen fixing legume) as a companion plant to Tomatoes, as an alternative to rotating crops in small growing areas. Organic Hairy Vetch Garden Seeds When it is time to plant tomatoes in