Romeo speaks through the poetic device of nature imagery less than might be expected considering how well known Romeo's most effective and famous example of the use of nature imagery is:
But, soft! what light through yonder window breaks?
It is the east, and Juliet is the sun.
Arise, fair sun, and kill the envious moon,
The brightness of her cheek would shame those stars,
As daylight doth a lamp; her eyes in heaven
Would through the airy region stream so bright
That birds would sing and think it were not night.
Lady, by yonder blessed moon I swear
That tips with silver all these fruit-tree tops--
In this famous and beautiful Capulet's Orchard scene (II.ii), Romeo enjoys flights of celestial fancy (at Shakespeare's hand) as he gazes upon the visage of young and fair Juliet who is silently musing about her encounter with Romeo Montague at the Capulet ball, as is shortly revealed:
O Romeo, Romeo! wherefore art thou Romeo?
Deny thy father and refuse thy name;
Or, if thou wilt not, be but sworn my love,
And I'll no longer be a Capulet.
In this instance of nature imagery, Romeo employs an extended metaphor to compare Juliet's beauty to the sun, moon and stars and to say that her face, her cheeks, her eyes would so outshine them all that if she were transported to the heavens, "the airy region," the birds would forget it was night, i.e., think it was day, and begin their singing. Later, during the balcony conversation, Romeo swears his love by the moon--one of the lights that Juliet outshines--until Juliet calls the moon "inconstant" because it changes in its aspect from one day to the next.
In an earlier instance, Romeo briefly uses nature imagery to speak of his prescient misgivings of impending doom and "untimely death" before he and his friends appear unwelcomed at the Capulet ball.
I fear, too early: for my mind misgives
Some consequence yet hanging in the stars
Shall bitterly begin his fearful date
With this night's revels and expire the term
Of a despised life closed in my breast
By some vile forfeit of untimely death.
But He, that hath the steerage of my course,
Direct my sail! On, lusty gentlemen.
Here, Romeo uses nature imagery to allude to astrology, which is said to read a person's fate written in the stars that govern their life from the hour of their birth to their death. Romeo uses stars to say that he believes some dire fate is hanging before him like stars hanging in the heavens (he is not thinking scientifically but poetically as stars do not "hang").
Another instance of nature imagery spoken by Romeo is his use of "flower" during one of the comedic ribaldry exchanges between Romeo and Mercutio:
Nay, I am the very pink of courtesy.
Pink for flower.
Why, then is my pump well flowered.
This exchange is most notable for how it contrasts with Paris's use of flower imagery in the closing act of the play when he goes to the Capulet tomb with flowers for Juliet (V.iii). Here, Paris is painted by Shakespeare with great sympathy showing that he loved deeply and would not have been so awful a husband for Juliet but for the fact of the mingling of the paths of the two star-crossed lovers, Romeo and Juliet.
Sweet flower, with flowers thy bridal bed I strew,--
O woe! thy canopy is dust and stones;--
Which with sweet water nightly I will dew,
Or, wanting that, with tears distill'd by moans:
The obsequies that I for thee will keep
Nightly shall be to strew [with flowers] thy grave and weep.