The seeds take about a month just to sprout, so start them at least 3 months before you want to move them outdoors. They need very well drained soil that is kept moist, but not wet. They are not frost hardy, so you might want to grow them in containers, which will make it easier for you to bring them indoors before the first frost. They may need monthly feeding, especially if in containers.
Here's a pretty good article about growing heliotrope:
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams