- Author: Jeannette Warnert
The summer months in Fresno County are ideal for garden soil solarization, an environmentally sound way to kill weeds, insect pests and soil pathogens with free and naturally abundant solar energy. No pesticides are used in the process.
The greenhouse effect of the sun's rays on clear plastic can heat up the top 12 to 18 inches of the soil to as high as 145 degrees under perfect conditions. Excellent pest control can be achieved by maintaining the soil at 110 to 125 degrees in the top 6 inches, according to the UC Integrated Pest Management Program. The hot soil environment will kill such pests as nematodes, grubs, cutworms, beetles and snail eggs. Disease pathogens, such as fungi that cause verticillium and fusarium wilt, die.
There are downsides. Solarization requires taking garden space out of production during the growing season for 4 to 6 weeks, but future garden success is likely worth the sacrifice. The process may also kill some beneficial soil organisms, though UC IPM reports that many beneficials survive solarization or quickly recolonize the soil afterward. Earthworms, often present in healthy soil, burrow deeper to escape the heat and return when the treatment ends.
To solarize soil, smooth an area and water uniformly to 12 inches deep, then cover it with clear plastic. Rolls of clear plastic “drop cloth” are available in the paint sections of large home stores and online. Thin plastic (1 millimeter) provides greater heating but is susceptible to tearing; slightly thicker plastic (1.5 to 2 millimeters) is better for windy areas. Secure the plastic tightly over the soil with shovelfuls of soil, lumber, rocks, landscape staples or anything that will keep the breeze from catching the edges. Leave the area undisturbed for 4 to 6 weeks or longer in cooler temperatures or if the area is shaded part of the day.
After solarization, the bed can be planted immediately with seeds or transplants.
Fresno County Master Gardener Emily LaRue is solarizing a garden bed at the program's demonstration garden, 1750 N. Winery Ave., Fresno. The Garden of the Sun is open to public visitors from 9 to 11 a.m. Mondays, Wednesdays and Fridays.
For more information on soil solarization, see the UC IPM Pest Note: Soil Solarization for Gardens & Landscapes.
We have endured multiple years of drought, and are probably in store for more. For many of us, it makes sense to replace all or part of our lawn area with less water-intensive plantings.
Step One: observe and plan. What existing trees and plants do you want to keep or remove? What are the sun and shade patterns within your yard? What types of grass grow in your lawn? Do you want any additional amenities, such as paving or a shade structure? How will you irrigate your new plants?
Step Two: kill your lawn. Homeowners can use two eco-friendly methods to kill their lawns: Solarizing or Sheet Mulching. For detailed instructions on solarizing, click here. For instructions on sheet mulching, click here.
Sheet mulching kills weeds by starving them of light. It takes 6 to 10 months and can be started any time of the year as long as at least three months of growing season are included. Sheet mulching works in sun or shade, and is effective on all grasses, including Bermuda grass, and many annual and perennial weeds. It is left in place permanently; over time, the dead lawn, sheeting, and mulch will break down into soil-enriching compost. Sheet mulching should be placed before new plants are installed if being used alone to kill lawn or weeds. It can be placed after plants are installed if solarizing has been completed first. New hardscape and irrigation should be installed before commencing solarizing or sheet mulching.
Step Three: replant. Whichever method you choose to kill your lawn, time it so that you are ready to replant in the fall, winter, or early spring. The cool temperatures and moist soils of our wet season allow drought tolerant plants to develop the healthy roots they need to thrive with little water during the heat of summer. Taking time to thoroughly kill the grass and waiting until the climate conditions are suitable for new plants will ensure the long-term success of a lawn replacement project.
UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu or leave a phone message on our Hotline at (530) 538-7201. To speak to a Master Gardener about a gardening issue, or to drop by the MG office during Hotline hours, see the most current information on our Ask Us Hotline webpage.
- Author: Margaret Gullette Lloyd
- Re-posted by: Gale Perez
From the Small and Organic Farm Advisor Blog
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The Heat is On: Soil Solarization
The days are long and the temperatures are high. This is a great time to solarize the soil in the Central Valley as a way to manage annual weeds and improve the growth of fall crops.
What is solarization?
A non-chemical approach to weed control, soilborne pest management and soil enhancement using solar heating of plastic-covered moist soil. This method allows the sun's radiant energy to be trapped in the soil thereby heating the upper levels, killing and/or suppressing soil pests.
Watch VIDEO: Laying plastic with a tractor for soil solarization
Why solarize?
- Kills or weakens many crop pests such as plant pathogenic bacteria and fungi, insects, nematodes and weeds within 2-12 inches +/- of the soil surface
- Soil physical and biological benefits
- increases levels of soluble, mineral nutrients available to the subsequent crop (nitrogen in the form of ammonium and nitrate, calcium, magnesium)
- generally less lethal to beneficial microbes than to plant pests
- increases breakdown of organic matter
- improves soil tilth
- Effects often last for multiple seasons, though best effects are directly after solarization
- Can work in combination with other pest management techniquessuch as steam, hot water, fumigants and pesticidal chemicals, biological controls, organic amendments (“biosolarization”), and host resistance
Watch VIDEO: Paul Underhill discusses how has used soil solarization
Solarization factors:
- TEMPERATURE: Solarization should be done in the warmest part of the summer. Usually this is between June and Augustin California. (See http://ucanr.edu/sites/solarization/california_air_temperature_maps/ for average temperatures for different months and locations in California.)
- TIMING: 4-6 weeks for maximum benefits (even 1-3 can provide some effects; time may be reduced with combinations such as biosolarization)
- SOIL PREPARATION: Soil should be as smooth as possible to get maximum soil-plastic contact. This can be achieved by finishing with roller or bedshaper, or working the soil by hand and removing any large debris or clumps.
- PLASTIC*: The most commonly used plastic is transparent polyethylene. Optimal thickness is 025-.03 mmunless solarization is being done in a particularly windy or animal-trafficked environment, in which case slightly thicker plastic should be used. Infrared-transmitting plastic can be purchased to facilitate a slightly higher temperature increase. Plastic with additives to decrease brittleness-causing sun damage can also be purchased.
- MOISTURE: Soil moisture should be at 70% of field capacityin the upper layers of the soil and moist up to 24 inches deep to obtain maximum benefits. It should crumble easily when squeezed. When moistened prior to plastic, soil should be covered as soon as possible to avoid evaporation. When done after, water can be added via drip lines, furrows or hose pipe outlets under the plastic.
- BEDS: Plastic can be laid in stripsover beds (min. 30” beds)or continuously for complete coverage. Strip coverage tends to be less effective than complete coverage because there is a cooling effect on the edge of the beds. For complete coverage, plastic can be installed by hiring a custom applicator, or can be laid in strips and joined by glue.
- BED SPECIFICATIONS: For strip solarization, wider bed tops will accumulate more heat. It is best to solarize on strips with north-south orientation rather than east-west, to minimize shading. Beds with no slope or a slight south-facing slope will yield optimal results.
- PLASTIC PLACEMENT: Plastic can be lain by machinery or by hand. It is important that the edges of the plastic are buried.
- REPAIR: If tearing occurs, plastic can be patched with patching tape.
Possible disadvantages:
- Challenges associated with plastic disposal
- Perennial weeds, bulbous weeds, and seeds with a hard seed coat are harder to control
- Climate factors, such as fog and wind, may impede solarization
- May decrease root nodulating rhizobial bacteria in the soil
- May increase purple nutsedge under certain circumstances
Further information:
Check out videos, how-to and the science of solarization here (http://ccsmallfarms.ucanr.edu/General_Production/Soil_Solarization/).
*Plastic can be sourced locally from Irrigation Supply Co. in Woodland. The price is $137.14 for a 60” x 4000' x 0.001” roll. Plastic is usually in stock, though should be ordered several weeks to months in advance for large orders.
References:
Elmore, C.L., Stapleton, J.J., Bell, C.E., & Devay, J.E. (1997). Soil Solarization: A Nonpesticidal Method for Controlling Diseases, Nematodes, and Weeds. (Publication No. 21377). Oakland: University of California Agricultural and Natural Resources.
Stapleton, J.J. (n.d.). Solarization for Vegetable Weed Control. California Weed Science Society. Retrieved from http://www.cwss.org/uploaded/media_pdf/59-67_2007.pdf
Yaduraju, N.T., & Mishra, J.S. (2004). Soil Solarization: An Eco-Friendly Approach for Weed Management. In Inderjit (Ed.), Weed Biology and Management. (1st ed., pp. 345-362). Dordrecht, Netherlands: Springer Science + Business Media.
Original source: Small and Organic Farm Advisor Blog
- Author: Ed Perry
Soil solarization is a simple technique that you can use in your home garden to reduce or eliminate many soil-inhabiting pests. Solarization works by heating up the soil in the presence of moisture to temperatures that are high enough to kill many fungi, nematodes, weeds and weed seeds.
In order to solarize your soil, you must leave a clear plastic tarp on the soil surface for 4 to 6 weeks during the hottest part of the year, which of course is now. Black or colored tarps will not allow the soil to get hot enough, so you must use transparent plastic. Polyethylene plastic 1 mil thick is the most efficient and economical, but you must handle it carefully because it rips and punctures easily.
Before laying the plastic down, clean up all weeds, debris and large clods, then level and prepare the soil as for planting. The closer the tarp to the soil, the hotter the soil becomes. Air pockets caused by clods or debris will decrease the effectiveness of the treatment. A smooth, bare soil surface is best.
You must also wet the soil before covering it with the tarp. The moisture causes organisms to be more sensitive to heat and also allows the heat to penetrate deeper into the soil. It's best to wet the soil thoroughly before laying the tarp.
While some pests may be killed within a few days, 4 to 6 weeks of treatment in full sun during the summer is needed to kill most pests with solarization. The highest soil temperatures will occur when the days are long and hot, and when the sky is clear and there is no wind.
Many disease organisms are effectively controlled with solarization, including the fungi that cause Verticillium wilt, Fusarium wilt and damping off of seedlings. Many annual weeds are also controlled, but perennial weeds such as Bermudagrass, field bindweed, johnsongrass, and yellow nutsedge are suppressed but not completely controlled by the procedure. Nematode populations are also reduced, but the heat may not penetrate deep enough to destroy those below the top foot of soil. Nematodes should be controlled well enough for shallow-rooted crops.
Once the solarization is completed and you've removed the tarp, take care not to disturb the soil very much. Turning the soil can bring up living weed seeds and diseases that were too deep to be destroyed by the heat.
Read the publication Soil Solarization for Gardens & Landscapes for more information.
- Author: Cheryl A. Wilen
Welcome to summer! Or at least I think it's summer since southern California is having a very strong “June Gloom” period that started before June and has touched July. You folks up north have had some pretty hot days though. That got me to thinking about solarization – the non-chemical process where soil is heated to a temperature that kills weed seeds (in this case) – by using the sun's energy.
Solarization is effective for controlling a number of different weeds species and on the surface (no pun intended), it's a pretty simple technique. Make the area smooth, wet it up, cover with clear plastic (be sure to tuck it in on the edges), and walk away for 4 weeks. It's also something that can be done on small spaces (although I don't think I would go much smaller than 25ft2) to many acres, provided you have the right equipment. Optimally, you would apply the plastic during the hottest part of the year but if you are in the desert, no need to wait until the daily temps hit 110, you are good to go pretty much anytime in the summer. For the rest of us mortals, generally August to early September will be fine.
Clyde Elmore, Weed Science Specialist emeritus, wrote a great blog about solarization about 4 ½ years ago so I'm not going to repeat it here. However, I invite you to take a look at it and also check out the newly revised Pest Note Soil Solarization for Gardens & Landscapes to prepare yourselves should you choose to try it out this year.