sunflower potting on question

Hi I have a mixed variety of sunflowers, the dwarf ones and tall ones are all in 3" pots and the dwarf ones are about 3 inches high, tall ones about 6inches high.  They all look healthy, should I pot them on into bigger pots now, for a bit or can I just stick straight into the ground.  My actual plan was to have them in the borders or in a oblong planter thats about 8" deep.

Never done them before.

thanks a lot
Amanda

Thanks thats great