Winter begins at the winter solstice (in December) and ends at the vernal equinox (in March).
Spring begins at the vernal equinox (in March) and ends at the summer solstice (in June).
Summer begins at the summer solstice (in June) and ends at the autumnal equinox (in September).
Fall/Autumn begins at the autumnal equinox (in September) and ends at the winter solstice (in December).