Solarization with clear plastic and tarping with black plastic help with weed management in high-value horticultural crops that otherwise need extensive hand weeding. Solarization tends to be more effective under suitably warm and sunny conditions, although tarping may be more suitable for some applications. With either practice, the plastic may be removed before planting, allowing for reuse, or left in place with holes cut through it to allow for transplanting.
University of Maine researchers give the following advice:
- Prepare a smooth seedbed before applying solarization or tarps.
- Apply plastic when soil is moist.
- Tightly secure plastic edges, especially for solarization.
- Minimize soil disturbance after removing the plastic to avoid bringing up new weed seeds.
- Consider incorporating organic amendments before applying plastic.
UMaine researchers found that solarization followed by flaming reduced subsequent weed emergence by 78 percent compared with a control that was flamed only.
Cornell researchers have studied the potential uses of tarps in organic vegetable systems to reduce or even replace tillage by controlling weeds and decomposing crop residue. They suggest that laying a tarp just three weeks before planting should sufficiently suppress weeds. Also, using tarps made tilling at 1 inch about as effective as rototilling at 4 inches, while non-tarped plots often had significantly fewer weeds and higher yield in rototilled versus shallow-tilled plots.
Check with your USDA-approved certifier about which solarization and tarping materials are allowed under organic certification standards.
Sources: “Solarization and Tarping for Weed Management on Organic Vegetable Farms in the Northeast USA,” By Sonja K. Birthisel et al., eOrganic, Aug. 28, 2018;
“Reusable Black Tarps Suppress Weeds and Make Organic Reduced Tillage More Viable,” By Haley Rylander et al., Cornell University, eOrganic, Aug. 22, 2018;
