Zilker Neighborhood Gardens

Commentary by a National Wildlife Steward who helps Zilker neighbors establish native plant gardens

The plastic soil solarization approach

It’s time for another round of soil solarization. If you recall, last year at about this time, I used the newspaper + mulch method to kill the grass to create a planting bed. Well, that approach was not very successful with our St. Augustine grass. It worked out OK but I had to go through and weed grass out of the beds twice before the fall when I finally planted plants in the beds. It seems most of our St. Augustine died and Bermuda grass volunteered in its place. So, now we are trying to kill Bermuda grass which is a bad, bad invasive.

So this time, we are using plastic instead of the newspaper and mulch approach. Following are pictures of the steps we took. There are varying views on if you use black or clear plastic. In my reading, I finally came to the conclusion to use black plastic in the cooler months (winter, spring) because it will also keep out the light that could help grass grow. In the hottest months, you should use clear plastic because it will allow all the sunlight through and create an inferno under the plastic. Whereas, black will reflect back some of the light and thus, not get as hot during the summer. So, ultimately we chose to use black plastic for the next few months.

Step 1: Draw out your design. First, draw it in your mind, then on paper, and then on the land. I used landscaping spray paint I bought at home depot ($5). That red line you see is paint. I am creating a semi-formal design so you can see the new bed on the right will mirror the bed I created last year on the left side. Using a measuring tape, I created the mirror image bed’s shape. Due to our lot size, sidewalk, and house placement, the right bed will be larger than the left bed. I decided to plant the oak tree in the round middle area in line with the house’s front window so you could see it from inside. Planting it dead center on our grass didn’t seem right (the grass on the far left is our neighbor’s). So you have to make some decisions like that. You don’t have to go out and buy paint – you could just use plain old baking flour and dust it along your shape. You could also use a hose to arrange the shape. Since I was not going to do all the steps on the same day, I didn’t use flour because it would blow away by the time I got to Step 2. The paint is permanent but quickly fades and would be mowed away within a few weeks if you changed your mind.

design your planting bed

Step 2: Scalp the grass. Next, we mowed the grass in this section as low as the mower would go. Then, we used a trimmer to scalp the grass down to the dirt. We tried to get every morsel of grass out of there (which is impossible) but the more, the better. It’s a dusty job – wear a mask if you can! When you are done, there will be a lot of grass shaving to brush up and put in your green waste bucket. If it is Bermuda grass, give it to the city’s green waste rather than your own compost. You don’t want that grass in your compost. We also took rakes and raked all the grass shaving out of the area to be swept up. I don’t recommend using a blower as there’s a lot of dirt now, and you’ll just create a big dust storm. Just use a broom to collect it and put it in green waste.

Scalping the grass

Scalp the grass










Step 3:Water the area deeply. Next, you want the area to be very moist. When you put the plastic on top, the moisture and the heat will allow it to become hotter and the heat penetrate more deeply. We turned on our irrigation sprinklers. After 15 minutes, I stuck a screwdriver down into the soil to discover that it was not wet at all. So we followed up with a local sprinkler to get just this area. Once adequately moist, it’s time to add the plastic.

Water more

Water the area deeply










Step 4: Lay down the plastic. As discussed already, we chose to use black plastic. I bought a role of 3.5 mil black plastic at Home Depot for $10. I thought it would be large enough for our area, but it was not. Luckily, we had some black plastic bags that we cut and duct taped to the rest of the plastic to finish the job. You really need two people to do this, and do not try it on a windy day (especially if you have only 1 person!!!). We cut a trench using our edger along the grass side so there was a slight trench into which could add the plastic. The deeper a trench you can create, the better to prevent whatever is on the other side of the new bed from penetrating into it.

We laid the plastic down and my husband shoveled up rocks we have available and we mounded those along the edge. Make sure the plastic is as flat and tight as possible to the ground. This helps heating as well as prevents wind from damaging the plastic or blowing it away. You should not have any holes in the plastic or the whole point will be sabotaged. Once we had our plastic in place, secured with rocks, I cut any extra plastic from the edges off with a scissors. Just after we were done a large, gale force wind came along, and our plastic passed the test!

Plastic in place

Step 5: Wait. Now we wait for several months for the grass to (hopefully!) die. If it doesn’t die off, we may recover with clear plastic in May when it gets hotter and see how that works. We suspect we will still have to do some digging to rid the area of deep grass roots that may persist. We will also put in metal edging to prevent grass from entering the area after our bed is created.

If you create a bed, know that you will always have to do a little weeding in it. There’s no 100% solution to weeds (a weed is anything you don’t want in your area). Even xeriscaped areas with rock will have weeds. But, I have to admit that I am LOVING my small gardens we’ve put in so far. I can’t imagine how happy I’ll be when the rest of the garden is done.

2 responses to “The plastic soil solarization approach

  1. Pingback: Soil Solarization … Update « Zilker Neighborhood Gardens

  2. Pingback: Soil Solarization … Update on the New Garden « Zilker Neighborhood Gardens

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