Rudbeckia seed heads should look dry and brown. I also watch for the stem below the blossom (i.e.below the seedhead) to start to discolor. That stem generally starts turning yellowish, then brownish.

If in doubt, you can leave the seedhead on the plant, tilt it a little, and rub the cone with your finger or thumb. Catch whatever drops in your other hand. You can see mature seeds if they're ready to harvest.

Ruds cross pollinate readily. If there are other cultivars growing close by, the seedlings might not even resemble cherry brandy.

Karen

Hmmm, don't think mine are quite ready then. The stems are still kind of green, even though the flower heads are mostly dry. I snipped off one and put it head down in a little plastic cup, uncovered. What the heck, worth a try. I'm just afraid that things are going to get soggy and nasty before the seeds are ready to harvest. Sigh, the bad weather and snow tend to creep up on me unnoticed.