Soil Solarization: May All Your Weeds Be Wildflowers!

Wildflowering L.A.‘ers – in particular those who battled weeds during the 2013-2014 Wildflowering L.A. project – as well as those of you reading this who are inspired by our collective project and wish to plant their own wildflower meadow this year….

Take note: it’s the time of the year to solarize your soil!

Only during hot, high summer when days are long and temperatures soar can gardeners perform soil solarization—a non-chemical control for soil-borne pests, including those dreaded weed seeds.  

The good news is: it’s not a difficult process and can easily be completed in just an afternoon with lasting effects. 

When done right, an enormous number of weed seeds are killed, meaning your 2014-2015 wildflower meadow (or your new native garden, if you’re converting to long-lived plants) will be more beautiful and easier to maintain. Less weeding is more time to watch the bees, butterflies and other beneficial insects that love to visit native flowers!

A group of staff and volunteers recently solarized Wildflowering L.A. Site #21 at the base of Wildflower Hill at the Theodore Payne Foundation in Sun Valley.

Here are the basics of solarizing:

  1. Clear the area of all plant material and any sharp objects such as rocks.
  2. Wet the soil thoroughly to a depth of 6″.
  3. Dig a 6″ deep trench around the perimeter of the area. 
  4. Lay clear (not black) 1.5-4 mil. plastic on the soil surface, stretching it tightly to the edges and down into the trenches. 
  5. Fill the trenches with soil to secure the plastic very tightly – as tightly as possible so that no air gets in. This way, the sun’s rays are able to penetrate and heat the soil.
  6. Leave the plastic in place for 4-6 weeks. 

For solarizing to work, you should see condensation (water droplets) under the plastic but no plant growth. Ideally, the soil will heat up to 140°F, a temperature that few weed seeds can survive!

Soil solarization works best in areas with full sun (no shade) and is most effective inland, where summer days are consistently hot and fog free.

SEE PHOTOS of the Theodore Payne Foundation’s solarization process on Wildlfowering L.A. Site #21 on Facebook. 

READ more about solarizing from the University of California, Davis. 

Happy wildflowering, all! 


Posted by Lili Singer, Director of Special Projects and Adult Education, Theodore Payne Foundation  for Wild Flowers and Native Plants