If you want to get rid of those weeds always coming up in your garden – solarize. Desperately desiring to drastically cut down on the number of insect pests for next seasons planting? Suspect you may have some root rot nematodes? Or some microscopic pathogenic bacteria villains creeping through your garden beds? Solarization may be a solution.
Solarizing is what scientists describe as the “greenhouse effect“
Using a lot of help from Old Sol, some elbow grease, and a few dollars, you can kill most weeds, their seeds, and insects and their eggs that might be living in the soil. Even though the process is the same a s the greenhouse effect, it is on a much smaller level, and no planet is harmed by the process.
The sun’s rays can heat the soil up to 140 F. This heat will destroy most seeds, insects, insect eggs, nematodes, and lots of pathogens. The pathogens – bacteria and fungal bodies that cause things like Southern blight, Verticillium wilt, root rot, damping off, and many other diseases are virtually obliterated by solarization.
Many beneficial organisms are killed by the process as well. However, many can withstand solarization or can quickly recolonize the garden. Mycorrhizal fungi rebound quickly as do fungal and bacterial organisms that parasitize plant pathogens. Earthworms, those workhorses of the garden, will generally dig deeper to avoid the heat and return once the process is ended.
In addition to killing all the bad guys, solarization also speeds up the breakdown of organic matter. This, in turn, releases nutrients into the soil and making them available to plants.
Solarization is particularly useful for destroying weeds. Bermudagrass, johnsongrass, nutsedge, field bindweed (morning glory), and other annual and perennial plant pests succumb to solarization.
Now that we know what solarization does let’s explain how to take the sun’s power and convert it to heat.
Purchase a roll of clear plastic sheeting long enough to cover the entire bed both lengthwise and across. The plastic should be 1 to 4 mils thick – although up to 6 mils can be used. Using black plastic is a misconception. Clear plastic allows the sun’s rays to penetrate through it, trapping the rays between it and the soil.
You can use the easy way to solarize, which I recommend, or, if you are on the meticulous side, you can use the more work-intensive method. It depends on your inclination. Let’s start with the easy way first.
- Smooth out the soil in the bed. Take out or break up clods.
- Fill in any holes in the soil.
- Thoroughly wet the soil in the bed to a depth of six inches.
- Spread the clear plastic over the bed and stretch it tight.
- Place stones or bricks, or really any type of weighted material along the edges of the bed, enough of them to keep the wind from blowing the plastic over.
- Wait four to eight weeks.
- Remove the plastic.
- Add organic compost to re-inoculate the soil with beneficial organisms.
It took me about 2 ½ hours to solarize a 40’X6’ raised bed garden.
The meticulous method:
- Dig a small six-inch trench around the entirety of the garden.
- Pile the trench soil onto the bed or, if you prefer, save it in a wheelbarrow or a tarp.
- Rake out the bed, spreading the soil well and breaking up any clods, but keeping it out of the trench.
- Thoroughly wet the bed down to a depth of six inches.
- Lay the plastic down onto the bed.
- Backfill one of the side trenches you dug with either the soil you took from the trench or other soil.
- On the other side of the bed, pull the plastic tight, and repeat number 5.
- Backfill both ends of the trench.
- Follow numbers 6, 7, and 8 of the easy method.
I have no idea how long this would take because I’ve never done it. However, I suspect it would take much longer than the easy method.
The best time to solarize is in high summer, from July until the end of September for those of us who live along the Gulf Coast.
Some folks keep the plastic on as a mulch, cut holes in it, and transplanting seedlings through the plastic. However, the plastic sheeting will start to degrade, leaving unsightly (and environmentally undesirable) pieces of plastic everywhere. I suggest you remove the plastic, discard it or save it for next year, and add organic mulch like straw to further keep weeds down.
While trying to lower my use of any type of plastic, I haven’t found anything that can replace it for solarization except glass. Perhaps scientists will come up with a new product shortly that can take its place.