While there are still some that are gorgeous, others have given their all and are ready for the seeds to be harvested.
Each dried flower head has many, many seeds, so you really don't have to gather each and every flower head, if you don't want to. Some people don't love the look of the brownish heads dying back in their garden. If you find yourself in that category, then you can collect the seeds from the dried up heads, and then pull out all of the rest of the plants as you're cleaning up for fall.
I have been cutting the dried heads when they become fully brown and dry, and then I just leave the others alone til it's their time to be cut. Since it's that time of year when things are naturally dying back anyway, I don't mind some brown here and there in my garden.
I kindof like cutting them when there is just a little bit left of the original color of petals left. That way next year, I can tell what color of flower I'm planting.
The smaller zinnias (like the photo below) don't have the same seed propagation, therefore you won't bother collecting seeds from them. These are some that I bought in a pony pack, and I'll just plant them the same way next year.
Isn't this a gorgeous time of year? I am so loving it and soaking it all in before the snows come. The other day, I was driving home, and looked up and had to pull my car over and gaze. The mountains are breathtaking with their amazing color and constant changes. I mean, even with the telephone lines and other obstacles, you can't help but be amazed at the beauty. Aaaaaaaaaaah. Fills the soul with good things.