Galadriel and Celeborn were married in the First Age and the story takes place at the end of the Third, so they were married for at least six and a half thousand years. During that time, they had one child. How often do you think they had sex?
It would be prudent for a sentient species with such long lifespans to practice planned procreation rather than multiplying exponentially like a culture on a petri dish.
There's the Elven Rope that's light as a feather and strong as steel. No reason there could not have been the Elven Condom that's thin and impermeable.
Thats weirdly more of a Warhammer fantasy hold over what with dommy mommy Morathi, mind you unlike the Aeldar they didnt murderfuck orgy Slaanesh into existance.
Dude it's elves who knows. She also slowes the passage of time by like MONTHS for a day, on top of being immortal it's pretty obnoxious. Maybe they only plow once a 1000 years, or maybe it's every day and they are only fertile once in thousands of years.