I’ve always understood this idiomatic English expression, applied to a person, to say that his prime has passed. This is horticulturally bizarre, because a plant that has “run to seed” is only guaranteeing that many more plants and flowers will appear in the next season.
The expression is supposed to hold because English people (who AFAIK invented the phrasing) believe flowers exist only for their enjoyment, not as plant genitals which by design must do all things genitals everywhere do. And it’s unsavory when they do, all those seeds and pods flying everywhere from wilted petals and deliquescing flowerheads. Given the regimentation of English gardens: gross.
Yet this song, by Düsseldorfers Strafe für Rebellion, expresses the more human understanding of having “run to seed,” and poignantly. Apparently the inclusion of vocals by young turkeys alludes to the more nature-oriented interpretation of running to seed. You decide, since I’ve overthought this enough.