You have a very long growing season in Houston, and it would make sense to do succession plantings of your zinnias. Some of the large flowered zinnias make a big seed set on their first few blooms, and the process of ripening all those seeds takes a lot out of the plant so that it will decline. Some of the smaller flowered zinnias, like the scabiosa flowered strains, can set and ripen seedheads all season while continuing to make new branches, and looking reasonably good.

If you want to extend the ornamental life of a zinnia, you could deadhead it, or just bring all the flowers in as cutflowers in vases. That will keep it from "going to seed."

If you are going to grow a lot of zinnia flowers next year, you will have the opportunity to save seeds from your favorite specimens, which will make you a breeder of your own zinnias. You will be surprised at how easy it is to improve your zinnias by saving seeds from your favorites.

And it is also easy to cross-pollinate them for added interest. Even if you don't cross-pollinate your zinnias, the bees will do some of that for you. But bees keep very poor records.

If you don't have any Whirligigs in the zinnia seed packets that you have, I recommend trying them. Whirligigs display many variations, and are interesting zinnias to grow for that reason.

ZM

I am retired now so I have the time to deadhead. I think I'll do that, but leave some plants to go to seed, that way I can have a longer bloom season but still get seeds for the following growing year.