From About.com Poetry:

I Know I Am But Summer to Your Heart

Edna St. Vincent Millary

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.

Wherefore I say: O love, as summer goes,
I must be gone, steal forth with silent drums,
That you may hail anew the bird and rose
When I come back to you, as summer comes.
Else will you seek, at some not distant time,
Even your summer in another clime.

Back Yard

Carl Sandburg

Shine on, O moon of summer.
Shine to the leaves of grass, catalpa and oak,
All silver under your rain to-night.

An Italian boy is sending songs to you to-night from an accordion.
A Polish boy is out with his best girl; they marry next month;
to-night they are throwing you kisses.

An old man next door is dreaming over a sheen that sits in a
cherry tree in his back yard.

The clocks say I must go—I stay here sitting on the back porch drinking
white thoughts you rain down.

Shine on, O moon,
Shake out more and more silver changes.

From About.com Poetry:

In the Mountains on a Summer Day
Li Po, translated by Arthur Waley

Gently I stir a white feather fan,
With open shirt sitting in a green wood.
I take off my cap and hang it on a jutting stone;
A wind from the pine-trees trickles on my bare head.

Poem 1386
Emily Dickinson

Summer — we all have seen —
A few of us — believed —
A few — the more aspiring
Unquestionably loved —

But Summer does not care —
She goes her spacious way
As eligible as the moon
To our Temerity —

The Doom to be adored —
The Affluence conferred —
Unknown as to an Ecstasy
The Embryo endowed —