Sorrel makes a lovely micro! It just takes a little time and patience.
Surface sow in soil, a light top cover of soil is fine, and occasionally recommended to help retain moisture for the seed. It does not need a pre-soak. An ideal soil temperature is 75°F (24°C) until germination, then reduced to 60°F (16°C). Bottom water or mist to prevent any mold forming on the seedlings. Maintain even moisture and do not allow sowing medium to dry out. It is typically ready to harvest in 16-25 days. Typically, microgreens are harvested at 1/2-2" in height, you can harvest at the cotyledon stage, or wait till true leaves emerge, this is usually recommended with red veined soil because of the pretty color. Hope this helps, thank you!