Ask Mr. Smarty Plants

First, let us ask you if you really need sod in that back yard? Is it required by a Homeowner's Association or do you need play space for children? If you don't have to have a sodded area, we have a neat idea for your garden that will solve several problems. Both St. Augustine and bermudagrass are non-natives to North America, and bermudagrass is extremely invasive, as well. At the Lady Bird Johnson Wildflower Center we are committed to the use, care and propagation of plants native not only to North America but to the area in which they are  being grown. So, we will look at answering your questions about drainage and fill, and then try to find the right solution for your purposes.

Drainage-you apparently are in some sort of neighorhood Homeowners Association, as the irrigation system is centrally controlled. By the same token, that association should have some knowledge of and control over drainage. Inquire if there are rules forbidding blocking natural drainage paths, and if anyone in your area has done so; thus, removing the water from their property and diverting it to yours. 

Filling-the clay soil is a big part of the drainage problem, as clay soil expands and holds water, and will permit no more to drain. Please read the section on "Soil Preparation" in our How-To article Native Lawns. In fact, if you are hoping to plant grass, this whole article will be of value to you. It suggests rototilling and adding compost, which is a good idea but if you have a sprinkler system with underground lines, you will need to get them located and avoid damage to those lines. Also, you won't want to cover up a sprinkler head with fill dirt. 

Next, lawn possibilities: the same How-to Article discusses the native grasses that can do well in Austin. One problem is that these all require a lot of sun and, once established, not much water. If you have no control over the watering, you are going to raise more weeds than you do grass. You have already established bermudagrass is not working in your area and, as noted before, is a non-native invasive.  St. Augustine is, while also non-native, is not as invasive and can survive in more shade and requires more water than the natives. 

Now, for the other solution we promised you. Sometimes called a "rain garden," sometimes a bioswale, there are other ways to get around your situation. Please read our previous answer on this situation, including all the links to other articles in that section. While this particular question came from Pennsylvania, it still addresses the question of clay soil and standing water. After you read this material, you will understand what we said about requiring sod or having a play area; a rain garden is neither. With flagstones for a path across it, and plants that will flourish, you will have a lovely area in your back yard, taking adantage of the conditions that exist.

We will go to our Recommended Species and search for plants in Central Texas that tolerate wet feet and can still survive being sometimes dry. You can follow each plant link to our page on that plant and find out more about height, care, light requirements, preferred conditions, etc. Because this IS Central Texas, and there are not many plants that tolerate standing in water for very long, you do need to address the drainage issues before you plant anything.

Central Texas plants tolerating moist or wet soils:

Amorpha fruticosa (desert false indigo)

Andropogon glomeratus (bushy bluestem)

Anisacanthus quadrifidus var. wrightii (Wright's desert honeysuckle)

Callicarpa americana (American beautyberry)

Conoclinium coelestinum (blue mistflower)

Liatris pycnostachya (prairie blazing star)

Lobelia cardinalis (cardinalflower)

Oenothera speciosa (pinkladies)

Physostegia pulchella (showy false dragonhead)

Taxodium distichum (bald cypress)

Quercus macrocarpa (bur oak)

From Our Native Plant Image Gallery:

Amorpha fruticosa

Andropogon glomeratus

Anisacanthus quadrifidus var. wrightii

Callicarpa americana

Conoclinium coelestinum

Liatris pycnostachya

Lobelia cardinalis

Oenothera speciosa

Physostegia pulchella

Taxodium distichum

Quercus macrocarpa