hey there Matthew. Years ago i made some seed bombs of various old seeds, including Ech purp, and turned out with no success at all, but thats not to say that 1. the seeds were tooo old (i know this is rarely true with wildflowers, but sometimes it is the case, as they were stored in a Greenhouse) or 2. might have been a problem with my
compost... in any case, i look forward to hearing what others have come up with.
I know Ech. needs to be wintered, whether in a fridge or in the landscape, they need some cold downtime before they will sprout. So, by chance you threw out some bombs in the spring with no results, wait a year and you might be suprised what comes up next year! good luck!