Texas climates are very unique. We do not have regular seasons in most of the State, and for those of us in the Deep South, Fall is one of the best times to plant. We have less bugs, less heat and more water. Herb gardening is often much easier than vegetable to begin with, so our resources here are to get you set up for success!
We are greatly influenced by hurricane season in the Fall in Central Texas, the Gulf Coast, and even up into NE Texas. Temperatures begin to back down from 100+ by about October, unless we get an early hurricane that sweeps the heat away. I like to get things going as soon as temperatures begin to dip into the high 80s. Be aware that many starts can still get burnt if we get a heat wave in Fall.
Fall is the perfect time to plant both perennials and biennials so that they have more time for their root systems to get established before the heat sets in. With climate change, our seasons are getting more deregulated, and I encourage experimentation rather than looking at traditional planting guides found at local garden shops. Due to almost regular flooding, its a good idea to due successive plantings of seeds, in case seedling gets washed out.
Make sure to walk the site and watch how the light falls, keeping in mind that the angle of the light will change depending on the season when starting new beds. You will also have to decide what type of beds work best for your site, which often times depends on the soil. For example, East of Austin sheet mulching works great, while in Hill Country West of Austin raised beds are a better choice.
I find that many annual herbs do best direct seeded, please see a link here for how to direct seed. I also like to integrate permaculture concepts like wicking buckets for my herbal experiments, especially in the spring. You may also want to integrate in the idea of guild gardening so that your more sensitive herbs are protected in the heat. Fall is the perfect time to get the guild started.
Start small, make sure your beds are ready, and give starts enough room to get established. More than anything have fun, and enjoy watching the life cycle of a plant. Once you grow, harvest, prepare and take the plant, it will completely change your relationship to the herb.