Most Coreopsis that you grow from seed are clump forming plants that will reach 2-3 feet. They hold daisy-like flowers on tall stems clear above the foliage. This growth characteristic makes it easy to enjoy the blooms in the garden, and to collect seed from your plants. No digging around the foliage looking for seed heads like with some other decorative garden plants. Collecting and saving Coreopsis flower seeds couldn't be any easier.
How to Save Coreopsis (Tickseed) Seeds
Here's a quick garden video on how to collect and save Coreopsis seeds. You can watch this seed saving tutorial in lieu of reading the post.
Shortly after the flowers have been pollinated the flower petals will fall and leave behind green 'buttons' where the seeds are forming. If you would prefer more blooms than seeds, deadhead the blooms by pulling off the spent flowers heads. Otherwise the seeds will begin to develop and soon the seed head will open up and out will spill the seeds. Coreopsis flowers and seed heads will grow at the same time on plants. So there is no "right" time of the year to harvest seeds. Collect your seeds are they develop on the plant. Don't wait until it has stopped blooming.
Here's a picture of two Coreopsis seed heads at different stages. On the left, is a seed head that has fully opened and the seeds have been dispersed. On the right, the seed head is just at the right stage of development for saving the Coreopsis seeds inside. The seed head is still tight enough that it is holding all of the Coreopsis seeds inside. To collect the seeds, just snip off the entire seed head.
You can pry open a Coreopsis seed head and carefully extract the seeds, but just crushing the seed head between your fingers is good enough. Inside there will be dozens of semi-flat, brown to maroon seeds. They supposedly remind people of ticks, which is why many call the plant "tickseed." And now you know how to save Coreopsis seeds in your garden.