That is odd about the aphids. I grow nasturtiums every year (because my mom loved them, called them "Little Nasties
), including this Alaska dwarf variety, and I've never seen an aphid on them. And I'd notice, too, because I like to pick the flowers and leaves for salads. I know there are aphids out there, because nearly every plant I bring indoors to try to overwinter shows up with aphids on it!