So there I was doing the Tribune Crossword last week and the hint was “The Cruelest Month”, and lo and behold, the answer was “April”. I hadn’t a clue. Why is April the cruelest month?
It’s a quote from literature. The opening line from T. S. Eliot’s “The Waste Land” to be specific:
Hope this helps. 
Up to a hundred years ago ,before the time of food preservation, by the time that April had come round most people would be short of food. What had been stored over winter had been used up or had gone bad . It was too early for anything to be growing in the fields and a lot of people would nearly starve.This was why it was considered a cruel month.
Not to disagree, but that doesn’t really have anything to do with it.
Eliot’s purpose in calling April “the cruellest month” (I really meant to stick a [sic] in there the first time, that is how it’s spelled in my edition) is to turn the commonly-used “springtime is good” concept on its head and instead show us that in the waste land he describes in his poem, springtime is cruel because it means the cycle of life leading to inevitable death has begun again. Granted, you wouldn’t get that from the very short section I quoted.
But the direct literary reference Eliot is making (if you know Eliot, you know this has to come up) is probably to Chaucer’s The Canterbury Tales:
If your Middle English is as rusty as mine, just take my word for it, it’s a much nicer image.