All you need to grow fine, vigorous grass is a crack in your sidewalk.

The line uses a homely, urban image—grass thriving in a sidewalk crack—to make a broader point about nature’s persistence and the irony of human effort. Rogers suggests that what we try hardest to cultivate (a perfect lawn) can be stubborn and difficult, while what we don’t want (weeds or grass in pavement) appears effortlessly. Read more generally, it’s a wry observation about unintended consequences: life and growth exploit small openings, often in spite of our plans and controls. The humor comes from reversing expectations—“all you need” is not care and attention, but neglect plus a flaw—turning a mundane annoyance into a comment on resilience and futility.