Do you mean surfinia petunias? If so, they're not frost hardy so should not be planted outdoors before mid May (in London and the West country) or end of May elsewhere. Best planted in hanging baskets or somewhere they can tumble downwards, because that's what they do, tumble, they don't grow upright. Keep well watered and fertilise weekly during summer, turn them out and throw them away come autumn. I've noticed that many people say to dead head these - I never do and they carry on flowering regardless, but you can deadhead if you think they look untidy.