This poem is all about silence. Look at those skinny lines, and all that white space they leave on the right side of the page. Listen to the way the poem takes a sentence like the first one and breaks it apart so that even a section of the sentence like "often before but not" (which normally would never have any pauses around it) gets bookended by little silences. All those line breaks insert brief pauses before we get to the next line. Plus, there are the natural pauses at commas and periods.
All that silence gets pretty loud, doesn't it? What's so clever about Williams's use of that white space is that silence is – wait for it – the absence of words. We know, we know. But before you roll your eyes and say duh! give us a minute to explain.
"The Widow's Lament in Springtime" is all about absence and loss. A-ha! Williams knew what he was doing. In a poem about absence (of the widow's husband), his use of silence, which is another kind of absence, reinforces his speaker's feelings of loss.
When the speaker does break the silence, all that empty space is still felt, and deeply. She sounds almost preoccupied, as her thoughts meander through her grief. We hear words that end one sentence at the start of the next, as she uses them to move from one thought to another: "closes round me this year. / Thirty-five years / I lived […]" and "with masses of flowers. / Masses of flowers / load […]" (6-8 and 10-12).
We also hear a subtle stressing of her emotional state when she adds on words that aren't technically necessary for getting her meaning across. For instance, instead of saying "Sorrow is my yard" she doubly emphasizes her connection with the sorrow by saying "is my own yard." Likewise, instead of just saying "they were my joy," she adds an extra emphasis on the fact that things have changed by saying: "they were my joy / formerly." This widow is focused on one thing and one thing only: the death of her husband. That focus is reflected in the very way the poem sounds.