Cosmos contain perennials and annuals. The species C. bipinnifida (think that's how you spell it!) is a popular half hardy annual. Flower heads left from now until autumn will produce fertile seed. The other species generally grown is C. atrosanguinea which has the chocolate scented flowers. This is a tender perennial that needs to be overwintered indoors.

are ok ,not sure which i got then, so shud i cut them bak after fowering and not pull em up. i grew from seed every year . thanks 4addvice

If yours are shades of white thro'pink to red/maroon then they will be half hardy annuals which means you need to sow seed every year. Lidl and Aldi both sell them for a pittance. The C Atrosanguinea is the chocolate cosmos. It is a tender perennial. Some places it can be left in the ground and split the root every 3 years or so or treat it like a dahlia and put it inside out of the danger of frost in winter.

arhh ok so i will b looking 4 those nxt year then , thanks scotgran