It's been years since I've grown it but I seem to remember dark, round and tiny seeds.

They will self sow a gajillion seeds but only some of them will make it to blooming size so there is no need to worry about having too many.

The seeds need light so keep the area free of leaf litter or mulch and just let mother nature do her thang. When the baby plants show up (often during the cooler times of year) you can then move them around if you need to or thin them if too many sprouted.

Thanks, John. They are in a crowded border, so I hope they can get some sunlight to sprout.