1912 in reference to microbes, from germ + -y (2). From 1889 in reference to wheat.
Entries linking to germy
germ n.
mid-15c., "bud, sprout;" 1640s, "rudiment of a new organism in an existing one," from French germe "germ (of egg); bud, seed, fruit; offering," from Latin germen (genitive germinis) "spring, offshoot; sprout, bud," which is of uncertain origin, perhaps from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups.
The older sense is preserved in wheat germ and germ of an idea; sense of "seed of a disease" first recorded 1796 in English; that of "harmful micro-organism" dates from 1871. Germ warfare is recorded from 1919.
-y 2
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.