I know I am but summer to your heart,
And not the full four seasons of the year;
And you must welcome from another part
Such noble moods as are not mine, my dear.
No gracious weight of golden fruits to sell
Have I, nor any wise and wintry thing;
And I have loved you all too long and well
To carry still the high sweet breast of Spring.
Saying she is not Autumn–when the fall harvest brings about plump “golden fruits”–and so has none “to sell” (i.e., give to her lover) 

I know I am but summer to your heart Sonnet XXVII