Pot marigolds (Calendula officinalis) were my favourite flowers this year. I do not remember where the seeds came from but I picked them myself and had them stored for a few years, yet they germinated perfectly. I primarily grew them for their leaves as food for Rocket (yes, tortoises can eat pot marigold, but not other marigolds, which might have the same English name but actually are not related to each other - English can be very confusing. It is always better to go by the scientific Latin name). They did not do very well until I moved them into direct sunlight. It is almost middle of October and they are still flowering.
When I was little and wasn't such a huge fan of creepy crawlies as I am now, the marigold seeds terrified me because they looked like a cluster of caterpillars. I'm sure you'll see what I mean when you look at the picture below.
I let the seeds dry on the plant and then cut the whole head off and let them dry thoroughly on a tray at home. Then I store them in a labelled paper envelope where they will rest until spring. With so many seeds already dried and many more forming, I will probably have more than enough for a nice flower border and more than enough tortoise food.