When we bought our home three and half years ago, we had a decent looking front yard of a standard lawn. It didn’t last long. We stopped watering it, let the weeds grow in in full force, and have used it as a driveway and a landing pad for almost a 100 yards of compost and wood chips to be delivered on. In winter and spring it would be green, and depending on how often we’d weed whack (not frequently) or providing we didn’t have a tarp spread out or a giant pile of dirt, it could be passible as decent. But basically, most often, our front yard looks like shit. I can only assume our neighbors look at our house as blight of the neighborhood and wondering what the hell we are doing. But this weekend, I took the first step to my landscaping the front yard, and solarizing the area by using clear plastic to (hopefully) kill the weeds.
If this area was a maintained sod lawn, conversion to a different landscape would be easy. I could just sheet mulch, plant, and call it good. But my front isn’t a lawn, its about 1200 square feet of plantain, sow thistle, dandelions, weed geranium, unidentifiable weeds, and of course, my nemesis, Bermudagrass. Some of these weeds aren’t inherently bad, but I don’t want them here, and the Bermuda is a constant, painful battle. I’d stab myself in the eye before I use an herbicide or intentionally support Monsanto, so spraying the area isn’t an option. Sheet mulching has had little success in the back yard on the Bermudagrass, so over the 4th of July weekend, we branched out to a new experiment to naturally kill the weeds: solarization.
I followed the guidelines for solarization and Bermudagrass management based on some awesome UC IPM documents that I found here and here. Solarization works as the same principle of global warming: the sun penetrates though the plastic (similar to the atmosphere), which traps the heat underneath, and therefore heats up the soil. It is a natural, non-toxic way for killing a wide variety of garden pests, but in needs to be done during the hottest times of the year. For Sonoma County, and California, that is July, which was the main motivation to get this done this over the long holiday weekend. When done correctly, it can heat the top foot to 18 inches of the soil, and killing weeds, pathogens, and nematodes.
Solarizing the Yard to Kill Weeds, Naturally:
The first step was to lightly cultivate the soil. We borrowed a rototiller from a friend in our urban farming network, and Matt did several passes over the yard. Normally, you don’t want to chop up Bermudagrass- its like Hydra, you cut off one head and 5 more grow back, but UC says its ok to do to a depth of 3″. We made sure not to go deeper than that, and I think using the tiller was good decision because it cut up a lot of the dead weeds that had accumulated over the years, which we raked up to expose the soil. You want to be able to get the plastic as close to the ground as possible, and without sticks or rocks to puncture holes, so this was a helpful way for us to achieve that.
The next step was to completely water the area. The guidelines were to water to a depth of 12″, which I know didn’t happen. With my clay soil, that would have taken for-ever-er, and used so. much. water. We alternated between running a sprinkler, standing there with the hose running, and just laying the hose on the ground and moving it every 5 minutes or so. I took advantage of the situation and ran though the sprinkler a few times, which was fun, but just leaving the hose running under the loose plastic seemed to work the best, and it made me feel better about less evaporation. We slowly worked though the yard: water an area, cover it up, water an area, and on and on.
Once an area was watered, we spread the plastic over it. We used clear poly sheeting, purchased from the local hardware store, that was 4 mil thick. According to the UC, you want to use clear plastic, not black, so the sun goes though and heats the soil. Black plastic will shade the weeds, which could work, but we want them to cook. You also want a thin plastic, so the sun can penetrate easily. 4 mil is about as thick as you want, thinner like 2 mil would have been ideal, but I was concerned that because this area gets full sun for the entire day, a thinner plastic would start to photodegrade, and break into small pieces. This is still a concern with the plastic I’m using, but I felt it might last a bit longer.
We found it was easiest to unroll and unfold the entire sheet, then position it to the area we wanted. We’d anchor one side, then stretch tight and weigh down the other side. We used rocks, bricks and boards to create an edge around the entire area, which is important so you can trap as much of the heat in as possible. It is recommended to actually dig a small trench, lay in the plastic, then top with soil to create an even more air barrier, but we had asphalt on one side and our ground is rock hard, so digging is a pain. Our sheet wasn’t wide enough to cover the whole yard, so we overlapped two sections by about 9″, and anchored with bricks every few feet. We got it as close as possible to the house, and stapled the edge up on the side of the wall.
Now, we just wait. It is recommended to leave the plastic in place for 4 to 6 weeks. During this time, the soil can reach up to 140 degrees, hopefully killing all those weeds. I stuck my soil thermometer though the plastic into the soil, and so far we’ve reached 110 degrees. I still see green though the sheet, but I’m hoping there is magic and weed murder happening under the cover. There is obvious moisture trapped underneath, which I think is good for helping conduct the heat. We plan on leaving it in place for as long as possible, then sheet mulching and planting cover crop to help break up the clay and add organic matter. When we remove the plastic, I’ll make sure to report back on how it went!
I’d love to know, have you tried solarization before? How did it work for you? Please let me a comment and let me know!