An explanation is found in Smith's Comprehensive Bible Dictionary. I found it as a footnote in the book Jesus the Christ by James E. Talmage:
There are three kinds of fig trees in the East:
Early fig, ripening about the end of June
Summer fig, ripening in August
Winter fig, larger and darker than the summer fig, hanging and ripening late on the tree, even after the leaves are shed, and sometimes gathered in Spring. The blossoms of the fig tree are within the fruit, and not visible outwardly, and this fruit begins to develop before the leaves.
Hence, the fig tree which had leaves before the usual time might naturally have been expected to have also some figs on it (Mark 11:13); but it was not true to its pretensions.