Weed seeds, plant diseases and soil-dwelling pests can build up in garden soils and emerge year after year to wreak havoc in flower and vegetable beds.
But if you keep an organic or no-till garden, you can manage many of these issues naturally using the sun and garden tarping.
Tarping is an ultra-simple gardening technique in which gardens or bare patches of earth are covered with plastic sheeting to raise soil temperatures and alter moisture and light levels.
Tarping is mostly used to reduce soil-dwelling pests, weeds and their seeds, and certain plant diseases, but it also is a handy way to remove grass or weeds before adding a new garden bed.
To complicate things a bit, tarping is a general term, but there are two main techniques: soil solarization and occultation. The main difference between solarization and occultation is that gardens are covered with clear plastic sheeting with solarization and dark tarps with occultation.
Surprisingly, clear plastic sheeting is better at capturing solar energy and raising soil temperatures, while dark tarps are ideal for blocking out light.
Solarization works best during the hottest part of the year and it basically creates a greenhouse-type effect by raising soil temperatures and “cooking” the soil. Studies have found solarization to be quite effective for managing some plant diseases, like blight and wilt, as well as nematodes, mites and certain weed seeds.
Occultation, on the other hand, “increases soil temperatures, brings soil moisture to an optimal level, and (most noticeably) almost completely wipes out annual weeds,” explains Jason Lilley from the University of Maine Cooperative Extension.
Essentially, weed seeds “germinate under the tarp, but then die due to the lack of sunlight,” Lilley said. Occultation can be used to manage existing weeds, but it can also target weed seeds that haven’t germinated just yet.
Whether you use occultation or solarization is up to you, but if you want to try out either of these techniques, the steps are basically the same.
Just remember, ambient temperatures need to be high with solarization, because clear plastic sheeting can actually promote weedy growth when used in cold weather. Occultation can be used in hot or cool temperatures.
To start, prepare your garden space by cutting down tall plants as low to the ground as possible. Don’t forget, solarization “cooks” the soil and occultation smothers plants, so you basically want to remove all the plants you care about before tarping!
After prepping the soil, water the area deeply until the top 6 inches of earth are damp. You may need to water several times to get the ground nicely saturated. Adding moisture encourages weed seeds to germinate, but it also helps raise soil temperatures.
Next, lay down your plastic sheeting — clear plastic for solarization or dark tarps for occultation. Anchor tarps to the ground with landscape staples, sandbags, bricks or stones, but bury the edges of the solarization plastic. Creating a tight seal around the soil is especially important with solarization since you don’t want any heat or steam to escape.
Leave the sheeting or tarps in place for four to six weeks, then remove the plastic from your garden. If any dead weeds remain, rake them away and start planting.
Tarping can help break the pest and disease cycle and reduce garden weeds. Like many other garden strategies, it works even better when combined with other weed and pest management techniques, such as companion planting, crop rotation, cover cropping and mulching.
If weeds, pests and diseases have been plaguing your garden, tarping is well worth a try.
