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You get fluff when you dry goldenrod flowers.
This is what the fluff looks like, on one dried flowerstalk. But that's normal, with goldenrod (Solidago virgaurea), so just strip the flowers off the stalk and put the lot into a glass jar into your cupboard.
New England Aster is even worse than Goldenrod. If you get half seedy-fluff and half dried petals, you've done exceptionally well. I leave the fluff in, and can't complain about its efficacy...