Cannot help you any at all, but what is the Orange Co. turf removal program? Are you required to remove turf, getting a rebate, or what? Just wondering.

Getting a rebate, $2 per square foot (so a little over $2,000 of expenses to be reimbursed). Going to plant California native plants.

You could "scalp" the lawn (cut super short) and then do cardboard over it and mulch over that so that your neighbors are not looking at a bunch of cardboard for months--the issue with cardboard is that it responds to alternate morning dew/hot day sitting in the sun by warping up--hold it down with something. The grass won't all disappear by November, so there will still probably be some digging and pulling involved.

One problem you are likely to run into is that when the winter rains
return, there will be some St. Augustine roots left that will start growing again.
This happened when I took out our St. Augustine back in 2006. This is
not a problem if you get out there and pull it out as it reappears, but
the grass can get tangled with what ever new stuff you put in, so be
alert to re-emergence.

You may also have Bermuda mixed in there with the St. Augustine, and that WILL come back, again and again, so be alert for that.

Oh, OK, Adam, I understand. Good luck with your project.

Is there a minimum amount of new plantings required?

Something I thought might work for you is to find plants for the minimum amount of planting and, once you're into the cooler months, get that area of grass out of there (do as thorough removal job as you can) and install your waterwise replacements. Leave the cardboard/mulch for the rest of the area...it could stay there for a year or more, depending on when you think all the grass is finally dead.

St. Augustine, like bermuda grass has runners, so smothering is not that effective. I suggest you read the information in the link below, and if possible, attend a lawn removal class at Tree of Life. It will save you a lot of headaches later. You don't want to be pulling grass out of your new landscape for the next several years. Unfortunately, Roundup is the best bet for this type of lawn. Spray, wait a few weeks, water to get the leftovers to grow, and then spray again.

If you search this thread, you will find a similar discussion about removing bermuda grass.

When you get to the link, scroll down a bit to download a pdf file about how to kill your lawn.

Kill Your Lawn

Have used black sheet plastic over areas to kill off grass. Cut grass as low as you possibly can, then use the plastic. The black plastic really heats up the soil and plants so there is fairly good kill

Clear plastic, not black works great for Marathon. For St. Augustine or bermuda, not so much.

Interesting...what is the reason behind that?

It seem like black plastic would make it hotter, but the reason clear works better is explained below.

Plastic material: In general, transparent or clear plastic is most effective for solarization, as the heating rays from the sun will pass through the sheet and be trapped to heat the soil below. Usually, black plastic is less effective because it absorbs and deflects part of the heat rather than trapping as clear plastic does. However, in cooler or coastal areas, black plastic is sometimes better than clear, because weeds won’t grow beneath it, as they will under clear plastic when the air temperatures are too low to kill them. In this case, the black plastic should be left in place for several weeks during the hottest part of the year.

Here's the whole article about solarization: Soil solarization

Bermuda has roots that can go down several feet. The plant will come back from those deep-down roots. St. Augustine roots are far more shallow--when I pulled out my St. Augustine, none of it came back, even after several years.

Just writing to provide an update.

I went ahead with the cardboard and mulch. First, I emptied all my compost and several bags of chicken manure onto the grass. Then, covered it with a roll of 4ft wide cardboard. I didn't mind paying $100 for cardboard because my costs will be reimbursed by the county offering the program.

Then, with the help of my father in law's truck we found some free mulch at a nursery. We thought this was great, though I wasn't satisfied with the coverage. We spread it evenly, but it was pretty thin.

It took a few more weeks but I found a tree company that sold "fine" mulch by the cubic yard. I ordered a delivery of 8 yards, with a yard of compost mixed in. This spread evenly and it is covered across the yard by about 4-6 inches of fine mulch/compost mix.

Closeup of the fine mulch, bricks for scale.

Here in Orange County it has been very hot this summer, approaching 100 degrees today. I've been watering it a couple times a week, and raking it over once a week. I've peeked underneath and the grass does not look happy. :) It's been covered for a solid month now in the heat of summer. I pick or spray the stragglers around the edges.

I am wondering, should I add some source of nitrogen to the mulch to help it decompose faster? Any suggestion? I spread some fertilizer on top of it and wet it down, but that might be paltry for the requirements. I need to plant by the end of November to get the rebate.

I think you could use blood and bone meal to help it decompose faster.

Everything looks as it should and all you have to do now is wait for the heat waves of late summer/fall.