Home Gardener habits develop primarily through trial and error, influenced by the Old Wives story. Most scientific research focuses on commercial agricultural practices that don’t necessarily extend to home gardeners, so there is no science to confirm or deny the value of gardening practices.
Now there is a new science examining one old-fashioned chemical-free weed control method. Soil solarization is not a new weed control practice for organic gardeners who have practiced “tarping” for many years, especially in hot climates. However, Dr. Sonja Birthisel studied it as part of her postdoc the study In 2018, mulching a bed prepared with plastic a few weeks before planting makes sure that even in cooler climates like the northeastern United States, we can reduce weed pressure on subsequent crops. a A study from the University of Perugia found in 2024 Its solar system was limited to 67% to 81% during autumn and summer, but it can reduce the growth of weeds in winter and winter by 94% to 96%.
What is solarization?
For scientific purposes, the solar system refers to the covering of soil with clear plastic. Turping refers to the use of black plastic. This is probably counterintuitive, not very effective at controlling weeds. Both practices can raise soil temperatures sufficient to kill dormant weed seeds. Research has shown that even at low temperatures it has the effect of suppressing weeds. Warm temperatures can encourage “suicide germination” that causes seeds to germinate but cannot grow under plastic.
How to Solarize Your Soil
The solar system is most effective in moist soils that move heat better. Moist seeds are susceptible to heat. Using a layer of clear plastic over two layers of clear plastic or black can be used to enhance effectiveness. The best combination of plastic sheeting and plastic lengths may depend on your local climate. However, once the bed is prepared for planting, the plastic must be applied and left for several weeks. This means that it should be done after the initial thawing of the soil, but before the average last frost day. Alternatively, you can prepare your bed in the fall and be in the sun all winter.
But plastic is bad
The news is bewildered for those looking to reduce plastic use. A time- and capable gardener may choose a more labor-intensive, natural way to kill weeds, rather than buying sheets of polyethylene that cannot be recycled when it is unusable. But for those facing permanent perennial weeds, or converting neglected lawns into new garden beds, soil sun alternatives may be chemical solutions. They have a way to minimize the impact of solarization plastics.
It may be possible to obtain used greenhouse plastic. If that’s not an option, buy a thick plastic sheet instead of film. Gardeners can remove thick plastic before planting for many years. If your community can recycle plastics, do so. Otherwise, if the plastic sheet becomes brittle and the pieces begin to break, dispose of the plastic sheet properly. Sending large plastics to landfills can be bothering you, but it’s better than breaking them down outside to drop the microplastics into the waterway.
Editor’s Note: This article was originally published on March 12, 2019 and updated in March 2025.
