When I lived in Isleton, a small town in the California Delta, I made friends with the editor of the local weekly newspaper. It was called The River News Herald and Isleton Journal and his name was Michael Duffett.
Duffett was the most formidably educated man I had ever met. Cambridge and all that. Given a chance after college to work for the British equivalent of Wall Street, or to live with the Bedouins of Saudi Arabia, he chose five years in Arabia. He later traveled throughout India and Japan. Did I mention that he met the Beatles?
Although our educational gap was wide, he tolerated me as a writer and a reader in a place that fostered few of either. With his kindness, I wrote an occasional gardening column for the Herald. His desk was impressive, always scattered with books in Arabic and Japanese, both languages of which he could translate into the other.
One day I read to him a humorous haiku I had written for my magazine private line. He looked bemused and immediately asked, “Where’s the seasonal reference?” Huh? “Haiku should have a reference to a season.” I had never read that about haiku, I thought it was simply matter of getting the syllable count correct. Not so.
In the moonlight,
The color and scent of the wisteria
Seems far away.
Trusting the Buddha, good and bad,
I bid farewell
To the departing year.
The crow has flown away:
swaying in the evening sun,
a leafless tree.
In the case of the first, the wisteria blooms in early spring. The second poem clearly references the end of the year. The third obviously takes place in winter. Not all traditional Japanese haiku refers to a season but enough does that it makes me want to include that element when thinking about such poems.
Examples taken from here (external link)