I notice that seed packets always say "Sow after danger of frost has passed." Obviously, the seed companies don't endorse planting by the phase of the moon, or they'd say so, wouldn't they?

But how do you know when the danger of frost has passed? That would require keeping careful records of previous years' weather and subjecting them to statistical analysis—something that was beyond the abilities of the average farmer. That's probably why almanacs were so popular. Almanacs could easily create the impression of having done scientific analysis of the data—whether they actually did or not is highly doubtful.

I think my father liked to collect and repeat advice he had heard, and he pretended to believe it, because he thought it made him appear wise. (He did the same thing with the Bible, by the way.) But he didn't necessarily practice what he preached. In reality, planting, like everything else, was more a matter of convenience and intuition than following rules.