"What if I have this great zinnia and I want to continue to propagate this same zinnia year after year after year?"

That's a good question. The simplest approach is to self it on a lot of its seedheads on the original plant. If the plant has growing room, you can get a dozen or more flowers on the original plant and several dozen viable seeds in each seedhead. You could get 500 or more seeds from the original plant. That can give you a reasonably large zinnia patch of zinnias from that chosen plant.

It is reasonable to assume that your chosen zinnia will have complex ancestry, which will make it highly heterozygous, and that patch of progeny will have a wide variety of recombinants. A relatively small percentage of the progeny will be "good" and resemble the original. It is possible that a few of them will actually be improvements on the original. But many of the progeny will be surprisingly different from the original. Some may be completely different, but desirable in their own right. My first generation progeny cull rates are typically 90 to 95 percent. I self and intercross the few good specimens for a second generation.

The second generation will have a higher percentage of on-type specimens and a lower cull rate. Successive generations will have a higher percentage of on-type specimens. It can take 5 to 8 years to get a reasonably pure open pollinated strain. You can speed that up by growing more than one generation of zinnias per year.

This process of successive selections to convert a hybrid to a true-breeding open pollinated strain is called de-hybridization. That is the method that was used to create most of the many varieties of zinnias that are commercially available.

None of the books on propagation mention it, but zinnias can be grown from cuttings. I have propagated several zinnias from cuttings just go get a larger stock of seeds to start my selections.

A third method of propagating zinnias is by tissue culture. I have dabbled with tissue culture of zinnias, but that is something I am still learning.

I have developed techniques for growing zinnias indoors, and that can be helpful in propagating cuttings, as well as allowing more generations per year. But zinnias are not a houseplant, and growing zinnias indoors requires special care. And I have a lot to learn about the micropropagation of zinnias by tissue culture.

ZM