Most edited publications do not capitalize the seasons of the year, and we know of no major style guide that recommends doing so. Spring, summer, autumn, fall, and winter are common nouns like any other. Think of them as similar to morning, afternoon, and night—terms that denote clearly defined periods of time but are not capitalized because they are not proper nouns.
As parts of official names, however, seasons are capitalized—for example, the 2012 Summer Olympics, the Fall 2011 semester.
According to folklore, Phil’s sighting of his own shadow means there will be 6 more weeks of winter. [Washington Post]
A second issue is planned for the fall, although the subject matter is not known at this time. [Los Angeles Times]
They will air in the spring, autumn and winter. [Guardian]
By autumn 2000, the parties who were to take the lead role in the project were substantially identified ” [Irish Times]
My husband, Steve, and I were as excited as kids on summer vacation. [Globe and Mail]
It was blue-sky thinking for Karl Lagerfeld, as he treated guests to a jet-set experience in Chanel’s spring-summer collection. [New Zealand Herald]
If last spring taught us anything, it was that even the mining sector is vulnerable to the market miseries unfolding abroad. [Sydney Morning Herald]