This is why...

I save the goldenrod all summer.  When the monarchs migrate from here the last thing standing is the goldenrod, and this is what they prefer, on their way down the road, and out to wherever they go.
All summer they feed on milkweed which apparently makes them taste just awful--and their caterpillars       as well--but in the fall they need the sugar that the goldenrod  has, apparently, to sustain them to the next resting place.  I leave stands of this stuff wherever it comes up, and my reward is seeing this.