planted sweet peas for the 1st time this year myself - and from the display ive got i dont think theres much you could do with these plants that will stop you getting a good show out of them - planted in a bit of shallow ground i topped up with some multi purpose compost, jst gave them a bit water with either liquid plant feed or tomato feed depending on what i was watering - and they have come away a treat - covered in flowers and smelling amazing.
all i did was follow the instructions on the pack.