Black plastic does not raise soil temperature as high as clear plastic and will not kill pathogens or fungi. But it can be more effective at killing weeds. Black plastic blocks the sunlight so that plants cannot produce sugars through photosynthesis.
Neither clear nor black plastic will eliminate every weed. Sturdy weeds can puncture the plastic and grow through either color. Heat- and drought-resistant perennial weeds or those with deep roots may be able to enter a dormant state and begin growing again once the plastic is removed.
Killing weeds with plastic will have different results depending on the color of the material. Clear plastic raises the temperature of the soil. This can kill weed seeds and roots as well as soil pathogens and fungi. It also allows light through the plastic, which can allow heat-tolerant or hardy weeds to survive. Clear plastic is most effective during the hottest summer months.
Crafting and creative projects have been part of Heidi Grover's life since she was old enough to reach the glue and glitter. Grover received a degree in creative writing from Utah Valley University and combines her love of crafting with her love of words.
Yes, the tarp brings with it moisture as it sweats, feeding the weeds and allowing them to germinate. But without the sun, those pesky weeds die off. Earthworms pop up to the surface of the plot and, finding nowhere to go, start moving horizontally, and in effect, naturally till your soil. While cooking the soil, fungi, bacteria, weed seeds and insects also are killed off in the dark, moist environment.
A drive through the countryside in early spring used to reveal stunning fields carpeted with yellow and blue wildflowers, daffodils, crocus and black-eyed Susans. Today, you’re more likely to see black plastic tarpaulin instead of colorful flowers covering the fields of rapeseed. Instead of using chemicals to kill weeds, the tarps smother them naturally, helping prepare the soil for planting. Black plastic weed control was inspired by European gardeners, and its use in growing crops ‒ from multi-acre organic farms to backyard plots ‒ has proved successful.
The Tarp and Moisture
Once the flowering or growing season is over, clean out your patch. Remove all previous growth visible to the eye, and if you’re covering grass, mow it as low as you can. Spread the tarp over your target, weigh it down heavily on all sides. The heavier the tarp, the less susceptible it is to heavy winds; then, let it go to work until it’s time to remove it. Shake the dirt and weed bits out of the tarp if it’s not too heavy, clean it off and store it for another time.
Much discussion and disagreement have occurred as to which is better: a black tarp that blocks out all sunlight or a clear tarp, which lets the sun penetrate. Researchers at the University of New Hampshire found that the black tarps had a success rate of 100 percent weed suppression, while clear tarps, although they killed the weeds and cover crops, didn’t completely suppress all the weeds.
Using cardboard to suppress weeds has been effective in low-wind areas; however, don’t lay the ink side onto the soil. Black plastic sheeting and black trash bags also are not recommended as they aren’t heavy enough or thick enough to prevent high winds from blowing them away. You’ll also have to watch for birds pecking through the plastic, creating holes for the weeds to grow.