- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual herb.
- Height: 30–60 cm (12–16 in.). Stem branched, bristly, usually clearly coarsely hairy.
- Flower: Corolla regular (actinomorphic), yellow, approx. 1.5 cm (0.6 in.) across; petals four, 7–10 mm (0.28–0.4 in.) long. Sepals 4, spreading. Stamens 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence an elongating raceme in fruiting stage.
- Leaves: Alternate, stalked. Blade coarsely hairy, irregularly pinnately lobed, terminal leaflet large. Uppermost stem leaves clearly lobed.
- Fruit: Many-seeded, densely stiff-haired, 3-veined, 2–4 cm (0.8–1.6 in.) long siliqua terminated by a flat, slightly curved, seedless beak the same length as the other siliqua. Stalk approx. 1 cm (0.4 in.). Seeds pale yellow.
- Habitat: Fields, wasteland, rubbish tips, gardens, railway yards. Sometimes cultivated and left over from old gardens or an escape.
- Flowering time: July–September.
White mustard is casual in Finland, even if it isn’t particularly rare. The yellow seeds that mature in its flat-beaked siliquae can be used to make mustard, and the rest of the stem makes good fodder. White mustard seeds are used whole to improve the preservability of pickles and soured vegetables because they prevent the growth of mould and bacteria. Their flavor is however not released. This only happens when the milled seeds are mixed with a liquid so that the enzymes they contain are activated to form a fiery mustard paste. Mustard’s aroma disappears quickly, which is why vinegar or lemon juice is often used to preserve the flavor. At home it is advisable to prepare mustard immediately before use, removing any need for preservatives.
White mustard is undoubtedly the most important raw ingredient in factory-produced mustard, which is of the most common kitchen condiments all over the world. Growing white mustard in Finland is unprofitable, but it is sometimes cultivated as a rotation crop to improve the land and repel pests, and even as a nectar plant for bees. Mustard cultivation seems to be gradually starting in Finland on a wide scale, however. Presently, thousands of tons of mustard are imported into Finland every year, mainly from Canada.
Paradoxically, very strong mustard doesn’t use genus Mustard species at all, but is rather prepared with black mustard (Brassica nigra) and brown mustard (B. juncea; also known as Indian mustard, mustard greens and leaf mustard) seeds from the Cabbage family. It is also possible to find these growing as casual aliens in Finland, but one would have to be very lucky – and of course very knowledgeable. Differentiating between even different genera of Mustard family plants is not easy – closely related mustards and cabbages are occasionally even grouped into the same genus.