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.
Corrosion is the loss of metallic properties of a metal due to oxidation and is accompanied by the formation of unwanted products. Copper, iron and aluminum metals all corrode over time loosing strength, lustre and electrical conductivity. Rusting is the corrosion of iron and readily occurs in the alloy steel.