For an eighteen-line song, "Spring" has more than its fair share of flowers, but that's really no big surprise. Flowers are often used symbolically to represent springtime and rebirth, as well as beauty and femininity. Shakespeare certainly employs these symbolic aspects here. However, the Bard takes this flower thing a step further. Things get really interesting when we consider what specific flower types represent symbolically and how these symbolic readings inform the song's interpretation.
Line 1: "Spring" gets floral from the very first line. First we have daises. Aside from signaling spring's arrival, these little yellow-and-white flowers pack a pretty good symbolic punch. Daises traditionally represent purity, innocence, and virtue. Symbols of virtue often accompany references to "maidens" and respectable ladies. The mention of daises in the poem's first line sets up some expectations of purity and honesty that don't quite get fulfilled as the poem develops. These expectations add to the sense of surprise we feel when the adulterous nature of the cuckoo's song is revealed. The poem's first line also mentions "violets" and specifically refers to their "blue" hue. That flower, like our pal the daisy, often symbolizes virtuousness and its color (violet) sometimes represents fidelity. So, to recap: the poem's first line gives us a bunch of floral symbols for innocence, virtue, and fidelity. No wonder the adulterous cuckoo song takes us by surprise.
Line 2: The poem's second line presents us with another flower (thanks, poem). This time we get "lady-smocks." The "lady" in this flower's name strengthens the symbolic connection between women and flowers in the poem. It also helps that there is a reference to maidens and "their summer smocks" in the poem's second stanza. It seems like Shakespeare wanted to make sure we didn't miss this connection. Got it? Good. For all you horticulturists in the crowd: what's another name for lady-smocks? Anyone? Anyone? If you said the cuckoo-flower you'd be right. Now we have a subtle connection between flowers, ladies, and adultery (remember that cuckoo-cuckold connection). Pretty sneaky, Shakespeare.
Line 3: "Cuckoo-buds" (different from cuckoo-flowers) are the last flower mentioned by name in the poem. There is some debate as to exactly what flower Shakespeare was referencing here, but because of that "yellow hue" description most people seem to believe he was talking about buttercups. The mention of cuckoo-buds makes that cuckoo-cuckold connection even more obvious. But wait, there's more. That "yellow hue" is important. The color yellow traditionally represents things like sunlight and goodness. But yellow has another side. In the Middle Ages, yellow had mostly negative associations including deception or disgrace. That field of yellow "cuckoo-buds" doesn't seem like such a happy, sunny image now, does it? It feels more like a reflection of the disgrace felt by all those married men who fear they're a cuckold. Bummer.