Plastic weed block nightmare
Is there anything I can do to about an old plastic (impermeable) weed barrier in my yard without removing 6-8 inches of soil that's on top of it? I went to THPRD's native plant sale this weekend and was all excited about planting my new preciouses (aka plants). I knew about the layer of weed fabric near the top of the soil that I would need to cut through, but what I hadn't realized was two things: 1. It wasn't as water permeable as I thought. The ground was completely hard and dry and devoid of life underneath. 2. About six inches deep was a layer of completely impermeable black plastic. This probably explains why even I have problems growing day lilies. I'm going to work on removing the top layer of weed barrier every where that I can get to it. But what do I do about the deeper plastic barrier? I think both of these may even go under the grass which really concerns me for the trees. I have a large, established maple that looks great and maybe has coped with this problem. But my young baby maple that I trans-planted (from a shady spot in the yard) last year didn't grow much this year. Is there any option or machine that poke holes in the ground 8 inches deep, like a lawn aerator or something that could poke lots of holes in the plastic? Or am I really going to have to dig up the entire yard? Any other ideas? Is eight inches enough for most plants? Could I remove the top barrier and bring a couple more inches of soil? How deep do most plants send their roots? Thanks! Elizabeth
Washington County Oregon
Thank you for your question, Elizabeth. I feel your pain, having discovered the same problem on the landscaped part of our acre 8 years ago! I removed a dozen garbage cans full of 3 mil. black plastic. Although it was back breaking, it was the best thing I did for my soil and plants. (And then I made the mistake of putting down the pervious landscape material that you can read about here: https://s3.wp.wsu.edu/uploads/sites/403/2015/03/landscape-fabric.pdf) I, too, found soil that was compacted, bone dry and—as I now know as a Master Gardener—essentially dead for lack of microbes, which are the ‘heart’ of soil health. The depth of roots depends on the plant. Grass can thrive with less than 6 inches. Large trees’ root systems—and the soil fungi that support them—can go down and out many feet. Maple trees and rhodies have shallow root systems, which is why they need mulch and wilt easily. Bringing in more soil helps the depth, but your plants are still barricaded from developing the strong, healthy root systems that they need to thrive. Poking holes in the plastic won’t make the situation any better than the pervious barrier, discussed above. Based on soil science (and what I’ve observed in the revitalization of our garden soil and the improved health of our plants), I’d suggest you bite the bullet and remove the plastic in its entirety. If you need more impetus, watch the documentary ‘Dirt: The Movie.’ Your plants and trillions of soil microbes will thank you! Good luck!