The adjective "learnèd" (meaning "well-educated") is a native English word that should take the grave accent even outside of poetry. Also "unlearnèd".
Interestingly, as an addition to the parent comment, there's a certain point in time where a lot of -ed words are often spelt -'d, which presumably is from the transitionary period between the expectation that the -ed was pronounced and today's general pronunciation.
e.g. "Long legged monster"