Star Trek: 10 Things You Didn’t Know About Vulcans

Every seven years (about), Vulcans are biologically summoned to return to their homeworld to play a very literalised version of 'F**k, Marry, Kill'. During the pon farr, a Vulcan must 'take a mate' or die, fight and kill or die, or meditate so much they probably wished they were dead. If nothing is done, the resultant neurochemical imbalance is likely fatal within days.

Suggested in various ways over the years with Spock, Tuvok, and Vorik, and not least in that song The Doctor sings, it would appear that Vulcans only have sex during the pon farr. The Star Fleet Medical Reference Manual even goes so far as to say that "The [Vulcan] male is only capable of sex approximately once in seven years". This was never meant to be the implication, however. As Original Series writer D.C. Fontana stated in Captains' Logs: The Unauthorized Complete Trek Voyages:

Vulcans mate normally any time they want to. However, every seven years you do the ritual, the ceremony, the whole thing. The biological urge. […] This every-seven-years business was taken too literally […]. We didn’t mean it only every seven years. Every seven years would be a little bad, and it would not explain the Vulcans of many different ages which are not seven years apart.

That seems to be the general consensus moving forward in Star Trek: Strange New Worlds. Spock, T'Pring, and Chapel certainly haven't… gone without for that long.