Bartlett on Gardening: Harness Helios

​​The longest, warmest days of the year have arrived. Gardeners living in hot, sunny areas can use this time to solve persistent pest problems using a practice called solarization in which sunlight heats the top two to six inches of soil above 110 degrees. The heat kills pests, pathogens and weed seed. Annual weed seed is more susceptible than those of perennials. Beneficial microorganisms are also affected, but their populations quickly recover.

Weeds that spread from rhizomes, such as nut sedge and Bermuda grass, are not killed. They are better controlled by selective herbicides. I have had good results with Grass-B-Gone and am using Sedge Hammer for the first time this year. It is easy to apply but takes several weeks to eradicate the nut sedge.

We backyard farmers do not practice adequate crop rotation. We plant our favorite veggies in the same area year after year. This leads to a concentration of disease-causing fungi and bacteria as well as a proliferation of nematodes (aka roundworms). Rather than let the land lie fallow long enough for the pests to move on or die, solarization allows a rapid return to gardening.

Solarization is a four-step process. First, clear the area of all vegetation, then rake the surface so it is level and smooth. Water the area deeply to make the microorganisms more susceptible to the heat. Finally, cover the surface of the soil with clear plastic that is 1 to 4 millimeters thick. The thinner plastic allows faster heating but is easily damaged. (It may seem counter-intuitive to use clear plastic rather than black, but black absorbs and deflects some of the heat.) Spread the plastic over the soil and anchor it around the edges by tucking the sheet into a shallow trench. Ideally, there are no air pockets between the soil and the plastic sheet.

The gardener wants to use the longest, hottest days of the year for this process. Cloud cover and wind decrease the effectiveness of the treatment. Generally the process is complete in four to six weeks. At the end, remove the plastic. When you begin gardening the area, for best weed control, use transplants rather than seeds to avoid disturbing the soil.

A botched attempt at solarization. Not only did these folks use thick black plastic, they just covered whatever was growing in the beds. But this is the only solarization picture I had!

After using the power of sunlight to cleanse the soil, the gardener should begin a program of crop rotation to prevent the return of pathogens. This is challenging in small gardens because one needs a minimum of four areas. The goal is to place closely-related plants in an area no more frequently than every fourth year.

​​There are seven major vegetable families, so in theory one can plan a four-year rotation schedule. The reality is that we may not want to grow all of them, and our climate limits what we can plant in summer. One does not need to plant vegetables in

a space. Herbs and cut flowers are great summer crops.

Sun goddess Ann Bartlett lives among a series of ornamental gardens, where she harnesses the sun to do her bidding.

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