This herbaceous biennial crop does not require much water and heat; it is suitable for warm, temperate and cool environments. It grows in medium-textured soil with a low acidity and salinity content that is well-drained and rich in organic substances. The bulb is characterised by its round shape or slightly elongated top, with silver-white outer skins and decidedly fleshy white inner skins. Red onions have an elongated round bulb and deep red outer skins.