From the garden
It is time to start preparing fall gardens. Days are sunny and warm, soils are warm, giving seeds a good start going into cooler weather.
A technique that was made popular in 2000s is solarization, an organic gardening practice that uses radiant heat from the sun to eliminate weeds and harmful soil pathogens. The technique is simple: cover moist soil with impervious plastic and allow the plastic to remain in place for at least 4 weeks.
Solarization is most effective in the summer months when the radiant heat is high and days are long.
During the period in which the moist soil is covered solar energy heats the soil and water molecules in the soil. The plastic traps the heat resulting in soil under the plastic heating to over 150 degrees F. Temperatures this high will sterilize the soil, which is the goal.
Moisture is critical in the solarization technique. Without moisture, the ground will merely be smothered. Smothering can be done with cardboard, plastic, or other material that blocks the sun. Weeds under the material may die because of lack of sun, but harmful pathogens are unaffected.
It is the moisture that conducts the heat throughout the soil. The soil will heat only to the depth of the moisture level. Moisture also is needed for seed germination. With the moisture seed dormancy is broken, seeds germinate, but seedlings are killed with the high temperatures. Be aware that solarization process is non-discriminatory; all seeds will be killed, weed or crop.
What kind of plastic is best? Any plastic will start the process going but the true solarization technique uses clear plastic. Clear plastic will heat the soil hotter than black plastic. Black plastic is also effective in heat buildup but the process is called tarping, not solarization.
To put this into practice, prepare seedbeds or raised beds by tilling and amending with organic matter to get them ready for planting. Moisten the soil. The soil does not need to be soggy wet but plenty moist. Then cover with clear plastic. Secure edges of the plastic or tightly weigh edges down to prevent plastic from getting dislodged by winds. Keeping edges covered makes a good seal and prevents heat from escaping.
Thickness of the plastic does make a difference. A 5 mil plastic sheet can be reused in subsequent growing seasons.
Ellen Peffley Harp, a retired professor of horticulture at Texas Tech University, writes about gardening for several Texas newspapers.
