Why did the old almanacs always recommend...

We can’t speak for other old almanacs, but certainly The Old Farmer’s Almanac has never recommended planting potatoes on Good Friday; our only recommendation has been to plant by the dark of the Moon. Further, all our research has turned up contrary advice — neither to plant nor to dig potatoes on Good Friday. It was thought the timing would produce poor crops. The Creoles of Louisiana believed that if the ground were cut open on this day, Christ’s blood would run out into the rows. The only exception we found was an old belief that seeds planted on Good Friday will thrive.