As production in the spring vegetable garden begins to wane with the approach of high summer temperatures, many gardeners assess what went well and what did not.

Assess spring gardening

Did weeds sprout too easily and vigorously? Did nasty bugs eat leaves and damage production? Did nematodes distort roots and retard the growth of the plant and the quality of the vegetables?

If the answer to any of these questions is yes, the home vegetable gardener might want to consider solarization of part or all of the garden plot before planting a fall garden.

Consider solarization

Even if the garden produced well, many gardeners use solarization as a way to prevent problems, particularly weeds that can arise by leaving garden beds uncovered.

  • Description

Solarization is an environmentally friendly and inexpensive way to use the sun to reduce weeds and kill harmful pathogens, insects and nematodes. Plastic tarps are laid on moist soil to concentrate the heat of the sun and pasteurize the soil. Seeds, pathogens, insects and nematodes present in the solarized bed are killed by the extreme heat.

Research studies at Texas A&M AgriLife Extension in 2011 and 2012 showed that soil temperatures under the plastic tarps can rise to 180 degrees, more than enough to kill weed seeds and garden pests. By contrast, bare soil rises only to 115-120 degrees.

  • Beneficial organisms rebound quickly

Although many beneficial organisms are killed by solarization, studies have shown that good things in the soil like mycorrhizae fungi and certain types of beneficial bacteria rebound in the soil very quickly, making solarized soil more resistant to pathogens than soil that has not been solarized.

Other beneficial organisms, such as earthworms, survive the solarization process. In the case of earthworms, it is believed they survive by moving deeper into the soil during solarization.

  • Weeds suppressed six months or longer

In the short term, all types of weeds, both annuals and perennials are effectively suppressed by solarization.

In the long term, the 2012 study by Texas A&M AgriLife Extension showed that most annuals and many perennials continued to be significantly reduced as much as six months or longer after solarization.

  • Increases availability of nutrients

Solarization improves soil tilth and increases the availability of nitrogen, calcium, magnesium, potassium, and fulvic acid. Solarized vegetable gardens produce greater yields.

Solarizing a vegetable garden

Plan to solarize for at least one month, preferably two or more during the hottest time of the year when the days are long and the sun is more directly overhead.

  • July through

    • September ideal time

    July, August and even September are ideal, fitting almost perfectly between the spring and fall vegetable gardens.

    • Steps

    First, remove all vegetative matter and till or turn the soil deeply, breaking up any clods that can create air pockets under the plastic. Then rake the soil as level as possible.

    Next, water with an overhead sprinkler to a depth of 6 to 12 inches. Moist soil will conduct heat better to greater depths, allowing seeds, pathogens and insects to be killed in deeper soil.

    This might require sprinkling for as long as 18 to 24 hours, depending on how moist the soil is to begin with and whether the soil has much clay in it. Very sandy soil does not retain water as well as loam or clay, making solarization less effective in sandy soil.

    Next, stretch a clear plastic sheet directly on the soil as flat as possible. Bury all edges of the plastic with a layer of soil to make sure strong winds aren’t able to pull the plastic away.

    Be sure to use clear plastic between 1 and 6 ml thick. Painter’s plastic sheets, available at hardware and big box stores, work fine, particularly in the appropriate thickness. If tears develop in the plastic, repair them with plastic tape to retain as much heat as possible.

    The whole idea is to create a system to retain heat in the soil for as long as possible and to get the temperature very warm and hold it during the day.

    Let the plastic remain on the area for four to eight weeks. Be sure to remove it before it begins to break down too much, making removal difficult.

    Layer of compost can be added when complete but without turning it under

    After solarization, you can cover the area with a layer of good compost if you desire, but do not turn it under.

    You do not want to bring any deep weed seeds to the surface of your newly solarized bed. Hopefully, you will have the benefit of a weed-free garden for a few months.

    Plant the fall garden and enjoy.

  • The Gardeners’ Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas A&M AgriLife Extension – Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at VictoriaAdvocate.com.

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