All 3 of the plants you mentioned will self-sow reliably year after year after year. For 30+ years I gardened in Zone 6 and discovered a wonderful combination in the verbena bonariensis and the tall orange sulphur cosmos. The verbena is a see-through plant but very sturdy and helped hold up the tall cosmos. The orange/blue mix of colors was eye catching. The verbena/cosmos were in a driveway entrance planting and backed by a clump of miscanthus. The location was on a hillside in full sun. This bed rarely received supplemental water and looked inviting year after year. Removing unwanted seedlings in the spring took some time (the verbena seedlings were nearly thick as grass) but it was such a carefree and lovely combo thereafter, that the spring chore was well worth it. Cleome was in another bed in full sun and also reliably self seeded. It looked good in the early part of the day but in the scorching heat of August, the flower would wilt and look faded in the afternoon. This bed did not get supplemental water either; maybe the cleome would have look perkier with an afternoon drink. Despite this, cleome remained a part of this sun bed for years. The seedlings of all seemed to remain in the general area of the mother plant(s) Â i.e. not 30 feet away. Other reliable self-seeding annuals I had in my Zone 6 garden were the red salvia coccinea (the hummers loved this one) and malva zebrina. Besides the striped purple flowers, the malva had lovely glossy foliage

Hi Karen, I have some pink poppies that I can trade and some no ID pink Cleome and Cleome "Rose Queen" which is rosey pink - both of which are self-seeding. I think I might have some others too, but I can check. I'll send you an email. Sue

I know that some seeds need light to germinate altho I couldn't off-hand tell you which ones so I'm posting a link which gives some info. Not all on the list are annuals. I expect that if the seeds fall naturally on a thin mulch there may be enough light for germination anyhow. I don't use a lot of annuals but do love those self-seeders whether annual or perennial. They are worth a lot in plant value altho I really need to replan my garden because I tend to let them take over. Here is a link that might be useful: flower seeds that need light to germinate

Winter sowing has more to do with the temperature being below the temperature for germination, does it not? If so, I would think you could winter sow in zone 4 right thru march. Just follow the directions on the winter sowing thread and wait for germination. It won't happen till the soil in the containers reaches the optimum temp for that seed, right? Maybe I got it bassakwards?