You can get seed from a head of cabbage if you grow it yourself. It is a biennial vegetable so it will grow the head the first year and if you leave it in the ground over the winter it will sprout seed heads the next year. You can buy seeds to plant or you can also find seedlings to transplant at garden centers.
Copper and bronze do not contain any iron, and only iron can rust (because rust is defined as iron oxide, a compound of iron and oxygen); so the answer is that steel will rust the fastest and copper and bronze will never 'rust'. But, yes, copper and bronze do tarnish, they do corrode.
Iron and steel rust when they come into contact with water and oxygen. They rust faster in salty water or acid rain. Aluminium, on the other hand, does not corrode easily, because its surface is protected by a layer of aluminium oxide. Iron is the metal most commonly associated with rust. Oxidated iron is called hydrated iron oxide, and it has the burnt orange color most commonly associated with rust.