If you google the seed company's name, you might be able to find out more from them. The publication in the link in this post is from NCSU and seems to be good information. They recommend 3-6" spacing and planting in August for fall and winter harvest. I haven't had creasy greens in more years than I can count! Where did you find the seeds?

Sandy

Here is a link that might be useful: Upland Cress