Darrell Blackwelder column: Solar soil sterilization kills plant pests

Published 12:00 am Saturday, July 16, 2022

During a gardening interest meeting last week, home gardeners brought up an issue. The problem was that planting the same plants each year in the same location can lead to fungal and bacterial disease buildup, as well as insects and other pest problems. Many have no choice because of limited gardening space and plant selection, especially fall plantings with limited plant availability. Unfortunately, plant rotation may not be an option. However, there may be a simple solution that will reduce diseases and insects in planting areas. Soil solarization utilizing clear plastic kills plant pests by heat treating the soil. Commercial vegetable producers in California use soil solarization to avoid using pesticides. Plastic placed over the soil raises the soil temperatures to 180 degrees, reducing most fungi, bacteria, insects and weed seeds. Now is an excellent time to consider this practice with the excessively hot temperatures we’re currently experiencing. Make sure the area to be treated is clear of plant debris.

The soil should be irrigated; this helps the heat penetrate deep into the soil. It’s important to keep the soil moist for best control. Cover the planting area with clear plastic. Do not use white or black plastic because it will not produce enough heat. Try to use UV light resistant clear plastic (painters’ plastic). Seal the edges of plastic with mounds of soil to trap the heat. The solarization process takes 6-8 weeks for best results. One drawback is that often good bacteria will also be eliminated in this process. Be sure to add ample compost and organic matter to replace beneficial bacteria.

Darrell Blackwelder is the retired horticulture agent with the North Carolina Cooperative Extension Service in Rowan County. Contact him at deblackw@ncsu.edu.