Ask Mr. Smarty Plants

We are having a little trouble envisioning these "hanging gardens,"  but will try to help you as much as we can. Basically, what you are telling us is that you are planning very large container gardens suspended in metal troughs in mid-air. Probably the best place to start is with some help with container gardening. Please follow these two links:

How-to Article Container Gardening with Native Plants

Video presentation on how to plant in containers from the Wildflower Center.

Since you have stated that these are metal and will be in full sun (in Austin) a lot of the day, you will need to select very heat tolerant plants. The fact that the boxes are of metal means even more heat stress. And, in the Winter, there will still be concerns because the roots of the plants will be encased in a thin skin of metal and a few inches of potting soil, with cold air on all sides. The root of a plant is the most susceptible to cold. From Clemson University Cooperative Extension, here is an article on Cold Damage. Also, a previous Mr. Smarty Plants answer on the insulation the earth provides. This is from a colder hardiness zone, but it illustrates a problem you may find yourself dealing with. We realize we are spending a lot of time on heat/cold issues, but we hope it will help you realize that you are presenting us with a real challenge in terms of the environment these plants will have to endure.

Now, having hopefully covered ourselves if you have plant failures, we will fulfill your original request. For plant sources, we are going to to our Recommended Species for Central Texas list.  Please note this paragraph at the beginning of that list:

"Texas-Central Recommended

Commercially available native plant species suitable for planned landscapes in Central Texas. Visit our Suppliers Directory to locate businesses that sell native plants or seeds or provide professional landscape or consulting services in this state. Visit the Organizations Directory to locate native plant societies, conservation groups, governmental agencies, botanical gardens, arboreta, and other plant-related organizations in this state."

This list has 157 choices, all recommended for Central Texas, which means they should be heat tolerant in Austin. Cold tolerance is a whole other thing. Using the selection list on the right-hand side of that page, we will select on "moist" for soil moisture, since you say you are preparing drip irrigation, but you need to be aware that most succulents need very good  drainage and will do better with some sand or degenerated granite or limestone in their soils. For Height Range we will select 1 to 3 ft., but if you want to try for taller plants, you may run the same search and select 3 to 6 ft. For Light Requirement, "sun." You can follow each plant link to our webpage on that plant to learn what its growing conditions are, what soils it prefers, when it blooms and what color, etc. We will run separate searches for each Habit. Please note that many plants on the Central Texas list really prefer dry soil, so you may find yourself rethinking the drip irrigation. We chose 15 plants of various Habits, but only have room for 12 pictures; be sure to read each webpage on that plant where you can learn more about it, and see additional pictures.

Herbs (herbaceous blooming plants):

Asclepias tuberosa (Butterflyweed)

Callirhoe pedata (Finger poppy-mallow)

Conoclinium coelestinum (Blue mistflower)

Monarda fistulosa (Wild bergamot)

Dichondra argentea (Silver ponyfoot)

Salvia coccinea (Scarlet sage)

Grass or Grass-like:

Bouteloua curtipendula (Sideoats grama)

Muhlenbergia reverchonii (Seep muhly)

Succulents:

Hesperaloe parviflora (Red yucca)

Yucca rupicola (Twistleaf yucca)

Yucca thompsoniana (Thompson's yucca)

Shrub:

Chrysactinia mexicana (Damianita)

Dalea frutescens (Black dalea)

Penstemon baccharifolius (Rock penstemon)

Salvia greggii (Autumn sage)