Calendula is sometimes called pot marigold but shouldn't be confused with Marigolds from the genus Tagets. Since they are in the Asteraceae family they also don't develop a single seed pod that makes collecting seeds extremely easy for the beginner gardener/seed saver among us, but the seeds are just as relatively easy to locate as the Marigold seeds.
Calendula flowers can be yellow, white, orange or a combination of two colors-- like the calendula I spotted at the medicinal plant garden walk. The petals of the calendula surround many small "flowers" that are pollinated, from my observations in the garden, by small insects butterflies, moths and beetles.
The petals around the tiny flowers are only there to help attract pollinators to the center of the bloom. After the flowers have been pollinated the petals will wither and fall, leaving just a button-like center comprised of numerous seeds. Each segment, marked with the arrow, is an individual seed.
The seeds will fall off on their own, sometimes they stay on until they are brown and dried, and sometimes they fall while still green. The trick is to remove the seeds when the plant is ready to release them before wind, rain or garden critters do it for you. I do this by brushing the "button" with the pad of my thumb. Get a better idea of what I mean by watching the garden video below.
When dried, either on the plant or indoors by a gardener, calendula seeds look like this. They are brown, spiny and curled. Save some seeds from your plants to grow again in your garden next year or to share with gardening friends.
When I'm not actively harvesting calendula seeds and sowing them in the garden, they still come back because they're scattered around by birds. Most of the calendula I grow is located in the shadiest spot in my garden against the foundation of the house where it doesn't thrive, but blooms enough to keep it around.
Every year I tell myself I will grow it in the sunniest spots because it is a low-maintenance garden plant that blooms like crazy up until the first frost and sometimes beyond. We already had a light frost in the garden this year and just yesterday I spotted one of these plants blooming in the garden when I was collecting the calendula seeds pictured above.