Start with omphalodes, which some people think of as a perennial forget-me-not, its star-shaped azure blue flowers floating above ovate to heart-shaped verdant green foliage.

Plenty of flowers are bluish, but it’s rare to find true blue in nature, says Naonobu Noda, a plant researcher at the National Agriculture and Food Research Organization near Tsukuba, Japan, and ...

Ranking near the top of this list is the charming Blue Thimble flower, Gilia capitata. It features finely divided, mid-deep green leaves that have a feathery appearance.

Roses are red, violets are blue. Except they’re not. They’re, er, violet. True blue flowers are exceedingly rare, and not for lack of effort. Plant breeders have repeatedly tried to nudge ...