Mustard is not easy to classify. It is a cool season vegetable here, although it grows until summer gets too hot. In cooler climates, it is a warm season vegetable. Whether warm or cool season, it provides more than greens. For agricultural applications, it is also a cover crop and livestock fodder. Its seed and seed oil have culinary and medicinal application.

Also, some consider mustard to be a wildflower, and some consider it to be a weed. Most but not all species that naturalized here are of the genus Brassica. None are native. Wild turnip and wild radish are similar and are also naturalized, but not as aggressively. Their bloom may be pink or creamy white. Most mustard varieties display bright yellow bloom.

Garden varieties of mustard have milder flavor and finer texture than wild sorts. They are sometimes available as cell pack seedlings, but grow like weeds from seed. Varieties for mustard seed might only be available online or from mail order catalogs. Mustard greens develop bitter flavor with age or bloom. Bigger lower leaves can develop coarser texture.