Sunflowers are tall and straight, tenacious posture; Breaking the shackles is presented to people with its power.
I found that every time I grabbed the soil under its feet, it would definitely bleed. As for meaning, I think it's the price of blood paid by sunflower in its struggle.
The sunflower in this poem symbolizes the heroic image of daring to challenge authority, yearning for freedom and being brave and fearless. It is probably "wealth can't be lewd, poverty can't be moved, and power can't be bent." -"Mencius Teng Wengong" such an image.