Elyse setting up solarization study

Solarization reduces chickweed seed survival near soil surface

Sustainable Agriculture Student Research Project

Effect of soil solarization on chickweed (Stellaria media) seed viability across burial depths

Elyse Farmer, Department of Sustainable Agriculture, 2025

Introduction

  • Soil solarization uses clear plastic to trap heat and kill weed seeds without chemicals.
  • Stellaria media (chickweed) is a persistent cool-season weed.
  • Little is known about how burial depth changes chickweed’s response to solarization.

Methods

  • Field study at KPU Farm, Richmond’s Garden City Lands
  • Completely randomized factorial design with two factors and nine replicates (18 plots) (Fig. 1):
    • Solarization factor (Solarized vs. unsolarized)
    • Burial depth factor (40 seeds per mesh bag at 1, 2, 4 and 8 cm depth) (72 bags)
    • Randomization scheme
      Figure 1. A plot map assisted with study establishment according to a pre-determined randomization scheme for a completely randomized design.
  • UV-resistant clear 6 mm polyethylene applied for 8 weeks mid-summer (July 12 – September 6, 2025)
Solarization study
Figure. 2. Study site in mid-summer, showing uncovered control plots and plastic-covered solarization plots. 
  • End of season soil temperature measured at each depth for all plots
  • Seeds recovered from buried bags and germinated in plastic bags on moist paper towel
  • Weed density measured immediately after solarization and six weeks after solarization

Results

  • Solarized plots reached higher temperatures at all depths.
  • Chickweed seeds from solarized plots had lower germination, especially at shallow depths (Fig. 3).
  • Field emergence of all weeds was lower in solarized plots (Fig. 4).
Chickweed germination by solarization and depth
Figure 3. Germination of chickweed seeds buried for eight weeks in mid-summer at 1-8 cm depth in solarized and unsolarized (Control) plots. Error bars denote standard error.
Figure 4. Weed cover in unsolarized plot (left) and solarized plot (right). Quadrat marks a one-meter square.
Figure 4. Weed cover in an unsolarized plot (left) and a solarized plot (right). Quadrat marks a one-meter square. 

Conclusion

  • Solarization reduced chickweed seed survival near the soil surface.
  • Solarization effectiveness decreased with depth.
  • Solarization can reduce weed pressure without herbicide application.

Acknowledgements

  • Isaac Hendrickson and Hugh Graham assisted with plot establishment and maintenance.
  • Micheal Bomford greatly supported and guided this study.

Raw Data