"Jacqueline" wrote in message .. .
I have a bed in front of my house (part sun, northern exposure) where I've
tried some annuals that are supposed to reseed (marigolds, sweet allysum,
coreopsis, and something else I can't remember now), but nothing ever comes
back. I'm wondering if there's something I should be doing to encourage
them, short of collecting seeds & sowing them the next spring.

It's a hit and miss thing. At my site, dianthus, asian lily, yarrow,
and coneflower reseed well, but other flowers (including black-eyed
susan, a relative of coneflower) don't. I know, only dianthus is an
annual. Try a dozen annuals and go with what works. If you get four
which reseed and have a somewhat staggered flowering schedule, you are
home. Collecting seeds and starting them in flats works as well.