- 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.
- Author: Jeannette Warnert
Dec. 4 - 8 is Healthy Soils Week in California. Learn more by following the hashtag #healthysoilsweek2023 and visiting the CDFA Healthy Soils Week webpage.
Soil and plant science students at Madera Community College are learning about the local soil profile by climbing into a five-foot-deep soil pit at the UC Master Gardeners' Three Sisters Garden.
The students are in an agricultural lab course taught by Dr. Elizabeth Mosqueda, who knew the best way to understand the different layers of soil is to personally see, feel and collect soil samples at different depths.
Mosqueda starts her soils class with a PowerPoint presentation and a video to introduce the students to the physical properties of soil – color, texture, structure, porosity and other characteristics. Using the USDA online soil survey tool, the students learn that the soil series is Hanford fine sandy loam and the horizon contains three other soil layers beneath it. Then the learning comes to life when the students arrive at the soil pit with trowels, sharp scraping tools and containers.
![Professor Elizabeth Mosqueda (in orange shirt) instructs her students at the soil pit in the Master Gardeners' Three Sisters Garden. (Photos: Sarah Del Pozo) Professor Elizabeth Mosqueda (in orange shirt) instructs her students at the soil pit in the Master Gardeners' Three Sisters Garden. (Photos: Sarah Del Pozo)](http://ucanr.edu/blogs/FresnoGardeningGreen/blogfiles/103516.jpg)
“In our case, you can't tell the different soils just by looking at it, but by wetting samples and then assessing it with your hands, you can determine the properties of the different layers,” Mosqueda told the students.
Mosqueda wasn't able to get permission to dig the pit elsewhere on campus, but the Three Sisters Garden, a two-acre area on the north side of the school set aside in 2008 for community and student learning, was open to the idea.
With financial support from a dean, the professor worked with lab coordinator Lukas Griffen, who operated a backhoe to carve out the soil pit. The pit is protected by orange fencing when not being used for education.
The Three Sisters Garden is always open to visitors interested in all aspects of gardening, such as vegetable production, flowering perennials, drought-tolerant plants and attracting wildlife. The garden also provides a peaceful respite for stressed students and faculty.
“Some visitors just want to walk around, and we also have tables and chairs for those who want to eat lunch or talk,” said Barbara Mattice, a Madera County UC Master Gardener volunteer and a garden manager.
She said the garden also supports the campus community by donating about 2,000 pounds of fresh vegetables harvested in the garden per year to the campus food pantry and by participating in campus events.
View a video of Dr. Mosqueda at the Three Sisters Garden soil pit:
![Measuring the soil pit depth. Measuring the soil pit depth.](https://ucanr.edu/blogs/FresnoGardeningGreen/blogfiles/103518.jpg)