mirabilis are easy to grow,sow the seed in normal compost,i just put them in pots and leave outside,some people soak the seed but they will germinate without this,once plant has grown,put in a sunny spot and water well,they will self seed all over the place.sow in spring about now,you can sow indoors to give them a head start.when flowers have died down,cut stems back or leave until they have started to wilt,they will flower year in year out and spread.