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Put that blazing sun to work

Now's the best time for soil solarization

Raised bed covered with plastic
Here's my raised bed, all ready for the sun to do its work.
(Photos: Kathy Morrison)

There's at least one good thing about our hot, no-rain summers: We can easily put the sun to work for us in the garden, solarizing our soil.

Why solarize? It's a natural way to control pests, pathogens and weeds.

My first 4-by-8-foot raised bed was built 20 years ago on the south side of our small backyard. This replacement bed, constructed with better lumber, is 18 or 19 years old. It was my tomato-growing workhorse site for a few years, until I joined my local community garden and moved tomato production there.

Since then the raised bed has had an erratic production history. Beans did well for awhile, and peppers two years. Onions went in at least one year. I most recently had strawberry plants there, but they were not happy and died more often than not. The survivors were moved to grow bags, where they are doing well.

Since I didn't have to plant anything in the home raised bed this year, I decided to try solarizing it to kill off any lingering pathogens (such as wilts), weed seeds or nematodes. We had an overgrown podocarpus tree nearby removed earlier this year, clearing the way for an intense solarization experience.

The soil needs to be soaked first for
solarization to work. Those remaining
podocarpus leaves also have to go.

The solarizing process is easy, for raised beds or in-ground planting areas:

-- Remove any debris from the site and rake it flat.

-- Water it well, down at least 12 inches.

-- Dig trenches along the edges where the plastic will be anchored.

-- Cover tightly with plastic; anchor the plastic with soil (and rocks, in my case).

-- Wait four to six weeks (or more) for the sun to do its work.

-- Uncover and plant. (Though I likely will do a soil test before I put any plants in.)

The plastic sheet I used is 1.5 mils thick, which is within the recommended range for durability. It's not perfectly clear, but clear enough. Black or colored plastic is not recommended. Rolls of clear plastic can be found at most home improvement stores -- look in the paint section.

My raised bed's been set up for a week now. The soil temperature's already up to 98 degrees and the underside of the plastic shows many nice bubbles.

I'll report back later in the summer on my progress. Meanwhile, here's a great guide to solarization from the UC Integrated Pest Management program, if you want to try it. If a video is more useful to you, the Sacramento master gardeners filmed a solarization guide for the 2020 Virtual Harvest Day; see it here .


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Dig In: Garden checklist for week of Sept. 25

This week's warm break will revive summer crops such as peppers and tomatoes that may still be trying to produce fruit. Pumpkins and winter squash will add weight rapidly.

Be on the lookout for powdery mildew and other fungal diseases that may be enjoying this combination of warm air and moist soil.

* Late September is ideal for sowing a new lawn or re-seeding bare spots.

* Compost annuals and vegetable crops that have finished producing.

* Cultivate and add compost to the soil to replenish its nutrients for fall and winter vegetables and flowers.

* Plant for fall now. The warm soil will get cool-season veggies and flowers off to a fast start.

* Plant onions, lettuce, peas, radishes, turnips, beets, carrots, bok choy, spinach and potatoes directly into the vegetable beds.

* Transplant lettuce, cabbage, broccoli, kale, Brussels sprouts and cauliflower.

* Sow seeds of California poppies, clarkia and African daisies.

* Transplant cool-weather annuals such as pansies, violas, fairy primroses, calendulas, stocks and snapdragons.

* Divide and replant bulbs, rhizomes and perennials.

* Dig up and divide daylilies as they complete their bloom cycle.

* Divide and transplant peonies that have become overcrowded. Replant with "eyes" about an inch below the soil surface.

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