samhain, I looked around for you, to see if I can help but found nothing about why yours aren't setting seed. I can promise you, though, that Alaska Nasturtiums are not sterile. Click HERE for information.

I'd evaluate your weather conditions, your soil, and your cultural practices, especially fertilization.

Thanks, rhizo. The other nasturtiums right next to them are setting seed just fine. It seemed odd to me that the Alaskas aren't. Well, I'll continue to check them.