Green’s Dictionary of Slang

a severe reprimand, a ‘telling-off’.

1646		Parliament of Women B4: If he cog and offer to kisse, and tell you that he will kisse you, bid him take you about the middle and kisse the heaviest end; or if he faile, she may read him a Juniper Lecture.
c.1698		B.E. Dict. Canting Crew n.p.: Jiniper-Lecture, a round scolding Bout.
1706		T. Hearne Collect. 10 June (O.H.S.) I: The Quaker read him a Juniper [mispr. Jumper] Lecture agt. Lewdness [OED].
1714		A. Smith Lives of Most Noted Highway-men, etc. I 156: She read the Baker such a Juniper Lecture, that he really wisht his Ears [...] both off.
1725		Bailey (trans.) Erasmus’ Colloquies 30: ha.: Go get you home and tell your Wife of your Exploits. thr.: She’ll read me a juniper Lecture.
1744		W. Ellis Modern Husbandman VII Pt II 142: When women chide their husbands for a long while together, it is commonly said, they give them a juniper lecture; which, I am informed, is a comparison taken from the long lasting of the live coals of that wood.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.