Solarizing with Black Plastic
I don't have a large backyard, and I didn't have a lot of grass to remove. But getting rid of grass is hard work (and my master plan is to be grass-free). When I removed the grass from my front yard, about half of it had died off over the winter, some I dug out by hand, and then the rest I killed with RoundUp to make digging out easier. It was hours of back-breaking effort.
When I decided the backyard grass needed to go, I talked to a landscape designer and she suggested I solarize with black plastic. This would be less work than digging it out alive, and more environmentally sound (and healthier for me) than RoundUp. She said I should keep the plastic on for a year because of Pittsburgh's climate, and recommended 6mm plastic for sturdiness.
How I Solarized
I measured my space and bought a close-enough sized roll of contractor plastic online. On an April afternoon, I rolled it out, trimmed it, pinned it down with landscape fabric pins. I also secured it with various bricks and pieces of wood I had around.
After it rained a few times (spring in Pittsburgh!) I realized it was pooling with water. I went to a big box store and bought a pack BTI mosquito control dunks to drop in the puddles. Fingers crossed I won't be patient zero for West Nile virus this year.
How I Should Have Solarized
After I solarized, I read online that there were more steps to solarizing than what I did! Some people recommend that you cut the grass short before you put the plastic down. This is good advice. My black plastic was "puffy" with tall-ish grass, which caused some of the water puddles until the grass died back and flattened. Now that the grass underneath is dead or in decline, there's less puff and fewer puddles. I'm fairly certain that if you start with super short grass, you will have fewer puddles and might not even need those mosquito dunks.
The other thing that I didn't do was water the grass before I put the plastic down. I have no idea what this step might do, but maybe it's important if you're in a dry climate. Pittsburgh is so wet and soggy in the spring that the clay soil underneath already had plenty of moisture. But, perhaps if I was doing it during a dry spell, it would've been helpful.
How's It Going?
Two Month Update
I'm two months into this experiment and the grass is yellow! For the first few weeks, it smelled like a barnyard, but now it smells normal. Occasionally I have to add more pins or rearrange my seams, but otherwise, so far so good.
One Year Update
Winter was rough on the plastic. Pieces would tear and get caught by the wind, so I’d add more bricks and flower pots and pieces of stone to keep it in place. Landscape pins were not very effective at this point because the plastic was so brittle. In February, Pittsburgh had a bad windstorm and two-thirds of the plastic did not survive. This was a shame, because I’d planned to leave the black plastic on while I planted in the spring, pulling it up piece by piece. In March and April, the exposed dead grass started to grow weeds and some of the grass was also regrowing. I wasn’t ready to plant yet, so I had decided to try sheet mulching to buy myself more time.