The seeds will be hard to miss. The entire stalk will be covered with small round balls which will turn to a tan then dark brown/purple to blackish color. Leave the seeds to mature (late in the season). You'll know they're ready when you rub your hand over the stalk and the seeds come away fairly easy. Watch that the birds don't eat them all up before you harvest.

Wait until the tops are thoroughly dry and brown. At that point the seeds will be ripe and ready to fall out of the nooks they are in. I generally put the cut heads into a bucket and let them dry further in the garage. After a month or two I can then shake the heads and get most of the seeds out. After shaking I will break up a few to convince myself that shaking is getting most of the seeds out. Almost all seeds are most easily collected after they have completely dried on the plant. The few exceptions are seeds that disperse soon after ripening, such as dandelions, which would be easier to collect a day or two before they were ready to fly. Most flowers or seed pods turn a dry brown or straw color when the seeds are ripe, and the seed are generally black, brown, or straw colored and their coats harden. Some seeds become quite hard while others, such as grass seeds, are not especially hard, but in almost every case the ripe seed is a lot harder than the soft immature seed.

A good rule of thumb to remember when looking at flower stuff and there is more than one type of thing that could be seed, is to test with your fingers. The seeds will hold together while the other stuff will crumble or if moist roll up in a ball. Viable seeds are always hard and will not easily crush/break under pressure. Remy

If you haven't planted the seed yet... You may want to check that they are viable first. Think of echinacea seed just the same as sunflower seeds. You have a seed husk or shell... And then you have the seed inside it. A cone will be full of husks... But they aren't all full of seed. Vaible ones will be hard... And bulkier then just an empty shell. You can pinch them between you finger nails... Viable ones are hard and don't do anything. It they compress between you nails... It's empty.