I would definitely use Red Yucca! Scarlet Penstemon (Penstemon triflorus), Coral Honeysuckle (might need support as it gets taller), Tropical Sage (Salvia coccinea) Flame Acanthus (some nurseries have the redder one), Four-Nerve Daisy (Tetraneuris scaposa), Yellow Bells (if you want a shrubby one), Golden-eye (Viguiera dentata, 3-6 feet)Damianita, Squarebud Primrose, Brown-eyed Susans, Cenizo (one of the more purple ones...also a shrubby plant), Gayfeather (Liatris sp.) and Hill Country Aster (Aster Oblongifolius)

Are these plants going to be in sun all day, on gravel? I can second the cold hardiness of the squarebud primrose, aka, I believe, calylophus. Mine is still green, along with the Blackfoot daisy, a prolific white bloomer. You will see both blooming along the roadways in a few weeks. If you want to keep them blooming until fall, however, I expect they will require occasional watering. You might run this topic by the salvia forum, where some botanical heavyweights hang out.

Copper Canyon Daisy bloomed right up to our deep freeze last week. It's more on the orange/yellow side.

Salvia Greggii is available in red and also kept blooming through the fall.

There's a great purple lantana out there.

Roses look great with Agave too.

Most sages are xeriscape and cold hardy here up north. They tend to be red and purple. Zexmenia(Zexmenia hispida) winecups (Callirhoe involucrata), various Yucca, and Texas (Fall) Aster (Aster oblongifolius) are my personal favorites.

If you're OK with the plants dieing back to the roots in the winter, lantana should work. The Dallas Red is nice and has come back every year for me, although it was very slow last year. I planted it in morning sun almost seven years ago. The Confetti I planted at the same time that gets afternoon sun came back faster last summer.

I took a vacation to New Mexico and collected a lot of seed from wildflowers that I thought had promise. Now to see if they can put up with Central Texas humidity. Apache plume, Rubber rabbit brush, 4 winged salt bush, desert asters, and several thick bush forming heterothecas ( stiff leafed false golden aster). I have many dessert mallows and penstemons from around the state. 50 seeds varieties in all. Many without names. I have one pink buckwheat that dies back making a gorgeous dark red cluster that it holds thorough the winter. I have my fingers crossed. They are all growing and have survived the winter in 4" pots placed on the ground with a cloth over them for a couple of nights. I love to experiment.

I have been growing cold hardy cactus. I am tired of having to cut off 200 lbs of melted slime off my large "old mexico" cactus 2 years running. I dug the whole thing out. I like the Santa Rita Purple padded cactus. Some varieties that have the O glocinaia (sp) strain are not that hardy but the O macrocentras and O. Santa Rita "tubac" are winners. They survived in pots. I also like the O. chenile, O Erineacea, and O.polycantha. I collected a Huge padded nasty needled Opuntia from the Valley of Fire State park that is gorgious but dangerous. I had a needle go in me and break. It just came out 4 months later. I forgot about it. I think I am naming it Sid Vicious Evil Twin. Sid Vicius moniker is already taken By a cactus sent to me.

I grow most of the plants mentioned above by others. and they take no care except cutting back to make bushy. There is one texas plant that I never seen grown in the trade but is gorgeous and that is Antelope horn milkweed. I also like Echenacea augustifolia and Crag lilly Echeandia texenis(not a show stopper but a nice fall bloomer that bees love), Dalea aurea, and False Gaura . I love my natives.

I love natives also! I just wanted to mention one little thing on 4 winged saltbush...it's a known allergen in the SW U.S. Don't know to what extent people are affected, but it showed up when I was tested for allergies. But if you have extras on some of those other natives, I'd love to try some.

Linda, I emailed you.