Answer: In my experience, self seeders do very well when the seeds fall naturally onto old rotted down bark mulch -- it seems to be an ideal medium and the roots make their way down into the soil just fine. The only possible problem is that the gardener will add a layer of fresh mulch and cover up the seeds so that they can't germinate the following year. If you mulch routinely in fall or early spring, it may well interfere with the self seeding. Fresher mulch is also far less hospitable a germination medium.
To harvest hollyhock seeds, wait until they are dry; this only takes about two or three weeks after flowering. Be careful when you do it because the "pod" will disintegrate in your hand -- you might want to hold a paper bag underneath to catch any stray parts.
Enjoy your self seeders!
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