The speaker starts by describing dandelions the way most people see them: bright clusters in yards, wisps drifting through summer air, flowers children pick for their mothers. Then the tone flips. Dandelions are weeds, a nuisance, something to chop down before they ruin a garden.
Midway through, the poem reveals that the dandelion is a metaphor. The speaker once knew a person like this, "a happy yellow dandelion" who still felt like a danger to their garden. The speaker decided he had to be removed, and now he is gone. The poem doesn't say how or why, which leaves the situation unsettling and a little cold.
The mood is uneasy and guarded. The last stanza repeats the opening idea, that dandelions seem cute but will destroy everything, and it sounds like the speaker is justifying a choice. Judging by the title, "french kisser," the person may have been a romantic interest, though the poem never says so. The speaker may be hiding regret behind that hard, defensive logic.