my sweet pea are 6 inches high,what is the best care for them

Have you pinched the tops out of them? By doing this the plants will be more 'bushy' - you will get more stems and therefore more flowers. Keep them well watered until they are established (it's pouring with rain here at the moment, so I won't need to water mine tonight!). Dead head them regularly, to keep them flowering through the summer. Good luck!

they are very greedy plants so fed regularly too