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Let the Sun Shine: How we’re eradicating weeds with sunshine, and you can too.

Updated: Jan 16, 2023

Something exciting is afoot in the patch of soil that will become VISTA’s Wildflower Garden. A process known as soil solarization is arguably one of the most fascinating of the landscape preparation tasks we’ve undertaken. Elegant in its simplicity, soil solarization uses the intense Florida heat to destroy harmful weed seeds in the soil.

A humble sheet of clear plastic tucked tightly over the planting area creates a greenhouse effect. Soil temperatures rise to as high as 140F near the surface, killing weed seeds, tubers and rhizomes.

Because the planting site for the Wildflower Garden originally was overgrown with Wedelia (Sphagneticola trilobata), it wasn’t enough to just clear the planting area. Wedelia is an invasive plant that was introduced to Florida sometime prior to 1933. It grows quickly and forms a thick groundcover, choking out the native plants in its path. Even though the planting site had been cleared and the weeds and plants removed, Wedelia is an intrepid adversary. Its seeds remain buried, and over time the vexing weed creeps back in. To make the planting area truly clear of Wedelia and ready for the new wildflower plantings, volunteers put soil solarization techniques to work.

Below are the steps they followed and you can follow too in your garden.

1. Volunteers dug a narrow trench around the perimeter of the marked area for the new Wildlife Garden. The trench created a place to tuck in the plastic used in step 4. Because the optimum time for soil solarization (June to September) coincides with Florida’s rainy season, volunteers had to redig areas of the trench after a downpour. If your garden area is small enough to complete all steps in a single day, you can reduce the risk of showers caving in your trench walls.

2. Raking the planting bed allowed volunteers to remove any rocks and debris and created a smooth surface for the plastic cover.

3. In the time between the intense downpour and the second trench digging, the ground had dried significantly. The last step before applying the plastic was to spray the bed with water since moist heat is most effective at killing weed seeds.

4. Finally, volunteers spread a sheet of clear 6ml plastic over the planting area, tucked the plastic edges into the trench and covered the edges with soil. This method holds the plastic tight against the soil to keep the heat in and prevent the plastic from coming loose in the wind.

With so much good help, volunteers finished all prep work and laid the plastic in between summer showers. And now we wait. The soil solarization process takes an estimated 4 to 6 weeks. The blazing sun will work its magic, and volunteers will continue to monitor the bed and hand remove any emerging Wedelia.

By early September, the site will be ready for soil preparation. In October the garden will take shape as volunteers plant around 400 beautiful native plants. We’ll keep you posted on the progress of this exciting new Wildlife Garden.

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