I knew about Bill Mollison's method of using a plank, had never tried it, but this seemed an ideal moment to give it a try. I used a small plank from a wrecked pallet, and immediately noticed the soil underneath remained moist for days on end without me having to water. Some three weeks later I saw small seedlings appearing and I could remove the plank. That's the day the picture shows, more seedlings have surfaced since, and I now need to thin. So, depending on your climate and soil, an old plank can indeed be a big help with germination.