How To Solarize Garden Beds To Eliminate Garden Pests In The Soil

How To Solarize Garden Beds To Eliminate Garden Pests In The Soil

A great way to eliminate garden pests in the soil, as well as weeds, is by using soil temperature gardening techniques, also known as solarization. This unique method uses heat energy from the sun to reduce the effects of soilborne diseases, pests and other soil problems. Solarization works well in all types of gardens, from vegetables to flowers and herbs. It can also be utilized in raised garden beds.

Soil Temperature Gardening

Soil temperature gardening involves the placement of thin, clear plastic over the soil, with its edges buried within an outer trench. Large rolls of plastic can be obtained at most home and garden centers. Plastic uses the sun’s heat to raise soil temperatures. In fact, when properly done, the soil can reach temperatures up to 120 F. (49 C.) or more. These high temperatures easily wipe out many soil-borne diseases and other garden pests in the soil.

It is important, however, that only clear plastic be used to solarize garden areas. Clear plastic allows sunlight to pass through more easily, which is vital for soil heat retention. Black plastic does not sufficiently heat the soil. Thin plastic (about 1-2 mil.) also yields better results, as sunlight is able to penetrate the plastic more easily.

Solarization is most effective during the hot summer months when the soil receives the maximum amount of sunlight, as this will kill weed seeds and soil pathogens deep down in the soil. Unfortunately, this is also the time when most people are using their garden to grow plants, so summer solarization is only practical if you have a large garden and are able to sacrifice a portion of your space every year. That said, it can also be effective to solarize for four to six weeks in the spring prior to planting and in the fall after harvest.

How to Solarize Garden Beds

To solarize garden beds, the garden area should be level and free from any debris. Generally, the area is tilled and raked smooth before placing any plastic. For better soil heat retention, the soil should be moist but not saturated. Moisture helps heat penetrate the ground easier. Most soil problems are also more susceptible to solarization when the ground is moist.

Before laying any plastic, a trench should to be incorporated around the outer edges of the garden. The depth can be anywhere from 8 to 12 inches and about a foot wide in order to secure the plastic in place. Once the trench has been dug out and the garden area raked smooth, the plastic is ready to be placed. Cover the entire garden area with the plastic, placing the edges into the trench and backfilling with the excavated soil.

Be sure to keep the plastic pulled tight as you go. The closer the plastic fits against the soil, the fewer air pockets will be present, allowing the soil to retain more heat. Once you have finished laying the plastic, it should be left in place for about four to six weeks.

Solarization enables soil heat retention, which in effect, not only helps eliminate most soil problems but also stimulates the release of nutrients presently found within the soil. Soil temperature gardening, or solarization, is one of the most effective methods of controlling garden pests in the soil and other related soil problems.

Nothing’s tastier than tomatoes picked fresh off the vine, but maintaining a vegetable garden can be hard work, and not everyone has room for one in the yard. If you’re looking for a simple solution to grow your own produce this summer, consider a raised garden bed. These large container-type gardens are filled with lightweight, nutrient-rich soil and can easily produce twice the yield in half the space. Because they’re in a contained space raised higher than ground level, they’re also easier to maintain—no hoeing or stooping to pull weeds. The tips ahead will help you plan, plant, and maintain a raised garden bed for bumper-crop results. You may never go back to traditional gardening.

What is occultation?

Occultation is similar to solarization, but opaque coverings are used instead of clear. While it may sound counterintuitive, fields covered in clear plastic become hotter than fields covered in black plastic.

Black plastic actually absorbs light, whereas clear plastic allows light and heat to pass through. So occultation takes longer.

Occultation typically requires at least four weeks to be effective. The longer you keep the covering in place, the more effective it will be, up to about six weeks, at which point efficacy begins to level off.

Common materials for occultation on a small scale include common tarps and cardboard. On a larger scale you can use silage tarps and old billboards. Since these materials tend to be relatively heavy, you can use sandbags, bricks or other heavy objects to weigh down the edges.

Why would someone choose occultation over solarization? While occultation takes longer, there are a few benefits. For one, the types of tarps used in occultation tend to be re-usable, whereas solarization tarps are thin and more prone to tears. Because opaque tarps are multi-functional, you may already have some at home.

Soil solarization

Use the sun to control weeds as well as bacteria and fungi

Managing weeds

Soil solarization takes advantage of the sun’s heat, trapped under clear plastic sheeting, to control many kinds of weed seeds as well as harmful fungi, bacteria, and some nematodes. The process is carried out in summer and works best in regions that have hot, sunny weather for 4 to 8 weeks straight daytime temperatures above 80 degrees F/27 degrees C are ideal. Solarization isn’t very effective in coastal climates with summer fog, nor does it work well in very windy areas.

Plan to solarize areas you intend to use for fall vegetables, ornamental beds, or lawn. Follow these steps:

1. Cultivate soil, clearing it of weeds, debris, and large clods of earth. It is important to get rid of growing weeds, because clear plastic ― unlike black plastic ― doesn’t halt growth of plants in the soil beneath it.

2. Make a bed at least 2 1/2 feet wide (narrower beds make it difficult to build up enough heat to have much effect). Carve a small ditch around perimeter and rake to level surface.

Soak soil to a depth of 1 foot: moist soil conducts heat better than dry soil and initiates germination of weed seeds, which will then be killed by heat.

3. Cover soil with 1- to 4-mil clear plastic use UV-resistant plastic if it’s available, since it won’t break down during solarization. Stretch plastic tightly so that it is in contact with the soil. Bury the edges in the perimeter ditch. An optional second layer of plastic increases heat and makes solarization more effective use soda cans as spacers between the two sheets.

Leave plastic in place for 4 to 6 weeks (8 weeks for really persistent weeds) then remove it. (Don’t leave it down longer than 8 weeks, or soil structure may suffer.) You can now plant. After planting, avoid cultivating more than the upper 2 inches of soil, since weed seeds at deeper levels may still be viable.

How Solarization Works

Whether as a preliminary step before mulching, or on its own, solarization is a formidable chemical-free weed-control strategy.

“Soil solarization is the practice of covering moistened soil with clear plastic for a period of weeks, to create a local greenhouse effect,” said Sonja K. Birthisel, a postdoctoral research associate at University of Maine, who focuses on ecological weed and pest management in a changing climate. Water molecules in the soil are heated up by solar energy, she explained, and in suitable conditions, heat trapped under the plastic yields temperatures hot enough to kill pests, weeds and some plant pathogens, too.

Solarization is most effective during the sunniest weeks close to the summer solstice, but it can also be effective in spring and later summer. Even in Maine in May, maximum soil temperatures beneath the clear plastic in Dr. Birthisel’s plots were typically around 100 degrees — “or sometimes as hot as 118.” After two weeks, she said, that “was effective for pretty substantive weed control.”

Her research in support of farmers is conducted on open fields, but she has advice for gardeners, too.

“If you wanted to take a piece of lawn and turn that into a garden, solarization would be a great first step,” Dr. Birthisel told me in an interview last year. “If you lay that down for several weeks, it’s going to do quite a number on your grass.”

Sonja Birthisel’s Solarization Tips

Solarization is more effective when soil is moist. Irrigate or wait until just after a rain to install the plastic.

To better trap heat, patch any holes and tightly secure plastic edges by burying them or weighting them down all around.

Avoid bringing fresh weed seeds to the surface by minimizing soil disturbance between plastic removal and planting.

When you are solarizing open soil, try incorporating compost before solarization. Many studies suggest this can increase pest control.

Controlling perennial weeds will likely require far more than two weeks of solarization.

More about Traditional Soil Preparation

If you’re interested in learning more about more traditional soil-preparation methods, John Jeavons’s classic book “How to Grow More Vegetables” has continued to be updated over the decades, and his YouTube channel has a seven-video series on his “biointensive method,” including a how-to on double-digging in the first installment.

The influential gardener and educator Alan Chadwick, who died in 1980, developed a “biodynamic French intensive method” that calls for turning and mounding up the soil, as shown in this video.

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Controlling Crabgrass in Lawns

Crabgrass is a common weed in lawns, but you can control it without harming turfgrass. Mow, irrigate and fertilize your lawn regularly so that the turfgrass grows strongly and out-competes crabgrass. Be sure to read any herbicide label to make sure the product doesn't injure your turfgrass (University of Georgia).

Set your mower blades at the correct height for the grass type. Irrigate your lawn weekly during dry weather so that the soil is constantly moist but never saturated and feed regularly (This Old House).

Garden Bed Weed Management, by Southern Trapper

Working a 9-to-5 job, I don’t have time to pull weeds every day so I sure won’t be able to do so during TEOTWAWKI when time and operational security are scarce. So, I have spent a lot of time experimenting with techniques to reduce weed growth and improve soil conditions that require minimal inputs and labor. Here I present three methods of preparing new garden beds and maintaining existing beds that require only hand tools. These techniques are particularly suitable for individuals who want to turn existing sod into high-intensity gardening as happened in March of 2020 when many suburban and urban homeowners frantically tried to turn lawns into beds when they realized the fragility of the food chain.

In addition, these techniques eliminate the use of small engine noises. During situations like the breakdown of civil order or hyperinflation, it may be very important for operational security to minimize small engine noises so as to not signal the presence of abundant food at a particular home. And for the elderly or ill, these techniques do not require much physical labor besides bending over.

1. Sheet Composting

The most popular of these no-till methods enrich the soil while providing weed suppression by blocking sunlight. I originally used this method of sheet composting to convert portions of my lawn into rich garden beds without a tiller or tractor. Also called lasagna gardening, the sheet composting technique uses layers of carbon and nitrogen biomass. Begin with a heavy layer of cardboard or if not available newsprint. Layer more carbon materials onto this layer. Leaves, [some types of] sawdust, [some types of] wood chips, or [some types of] rotten logs are ideal. Then cover with nitrogen-rich material such as kitchen scraps, lawn clippings in small amounts, or animal droppings. Keep layering nitrogen and carbon until you have at least 2’ of material. I have found that you want at least around an 8:1 ratio of carbon to nitrogen. And also, be careful not to put “hot” nitrogen materials like chicken litter immediately on top of your base cardboard layer as it will quickly reduce the ability of the base to block sunlight. In arid climates, water occasionally.

How long it will take for the compost to cook will depend on your area, but we have been able to plant in 4-6 months after laying down all the material. Sheeting composting in fall or winter when you have access to leaves is a perfect time to prepare for spring planting. When it is time to plant, simply take a spade and dig right where you want to put the transplant or direct seed. Leave the rest of the bed undisturbed. When beginning sheet composting, it is easiest to plant transplants or tubers. However, it is certainly possible to direct seed. You can work the seeds into the layer of compost without disturbing the soil, though in our experience this may result in uneven germination. Or, simply dig a 1” deep by 3-4” wide trench with your hoe. Plant seeds in a trench and then, after thinning, throw compost heavily around the small plants as you have disturbed the weed bed in the trench. For plants like watermelons that grow best in a mound, I’m not shy about pushing the dirt around, but I then place sheets of newspaper to cover the mound except where the seed was placed.

Using sheet composting substantially improved my soil and yields, and it provided a very low tech way to convert sod into productive land. I would recommend using this method now while many of the inputs are easily available. Cardboard is very easy to source from appliance or grocery stores. When I go into town in the fall, I pick up more than enough bags of leaves on the curb. And while I would never buy a cup of coffee at a certain coffee chain due to its support of evil, I will take their coffee grinds for free which they give you if you ask.

However, I would not recommend using sheet composting solely as your method of bed preparation in a crisis situation. It is very hard to acquire enough inputs (compostable materials) to scale up production even at a time when you can simply pick them up off the curb. In TEOTWAWKI, it would be extremely difficult for most people to gather enough inputs. In addition, there is a risk that during subsequent years of sheet composting you will develop intractable perennial weeds. For this technique, the primary mechanism of weed control is blocking sunlight from weeds while minimizing exposure of the layer of soil that contains weed seeds (the weed bed). However, unless one is consistently putting down very thick and large amounts of opaque material, you are not killing the weeds but simply retarding their growth. We have found that after 3-4 years of sheet composting that we develop significant problems with Bermuda grass infiltrating the bed. This plant grows via rhizomes so it spreads its roots underneath the composting layer, and it grows up immediately when the bed is disturbed or the material cooks down.

2. Solarization

If you have ever laid a windowpane on the ground during a project, you will know that when you come back a week later you will have bare dirt. Solarization traps sunlight to increase the temperature of the soil and vegetation. In addition to substantially killing existing weeds and weeds in the weed bed, this method has benefits for controlling fungi, nematodes, and other pests. Studies have found a 94% reduction in weed seeds in solarized beds compared to non-solarized beds (Masabni and Franco, 2017). To solarize, you can either till or simply scrape the soil with a hoe to remove as many plants as you can. Lay down clear plastic. Painter’s plastic is standard, and I would recommend at least a 3 ml thickness. Non-standard sources for foraging in a crisis include shower curtain liners or clear vapor barriers on insulation. Leave the plastic in place for at least four weeks. For spring planting, we laid our plastic down in the last week of January. Since it is darker and colder now, I am going to keep it down until I am ready to plant in 3 months.

Once I am ready to plant, I will take the plastic off and move it to another plot to prepare the bed for summer planting. I cover the active bed with a layer of rotted compost (leaves from the fall, chicken litter, rabbit droppings, and kitchen scraps) to provide a layer of mulch. I run drip irrigation on top of this and then a light (2”) layer of new leaves but hand watering is of course a fine option. After you harvest, it best to cover up the soil. An easy way to do this is to plant a cover crop like rye or clover. Direct seed the cover crop by lightly working the seeds into the layer of mulch and then water well. Mow it down and compost or feed to the animals when you are ready to solarize again.

3. Occultation

The final method of no-till garden management is similar to solarization but has a different role in the survival garden. Like solarization, occultation raises the temperature of the soil through the greenhouse effect. The opaque plastic of occultation also prevents sunlight from reaching the plants and seeds in the bed, unlike the clear plastic of solarization. Because sunlight is deflected, there is a relatively lower increase in soil temperature compared to solarization. To use occultation, clear debris and plant material using a hoe then tightly fit a tarp or black plastic over the bed. Leave in place in at least 6 weeks and spread compost and plant without tilling.

Compared to solarization, one advantage of occultation is that a tarp is more likely to be found in the prepared household. Tarps can also be reused more times than painter’s plastic. In addition, occultation may harm pose less harm to the beneficial microrganisms of the soil compared to solarization which has more of a sterilization effect (Smith et al., 2017). One disadvantage of occultation is that it takes longer to provide adequate weed suppression. Smith and colleagues (2017) found a complete removal of weed seeds from the weed bed at four weeks using solarization but only a significant reduction of weed seed count at six weeks using occultation.

Putting the no-till garden together

All three techniques are suitable for gardening in an austere environment, and particular application will depend on your available resources and context. For improving existing beds, sheet composting in the offseason or solarization followed by mulching with compost are very effective techniques. If sheet composting, I would still recommend periodic solarization after the organic matter has completely broken down to reduce the weed bed. If converting sod into productive land, I would suggest mowing the grass as short as you can and then using occultation to kill at least the visible grass. Next, use sheet composting for at least the first season to improve and aerate the soil. After a bed has been established, plant cover crops followed by seasonal solarization and mulching with compost.

Watch the video: The Result of Using Black Plastic Over the Winter