Courtesy of Ed G., Davis CA:
Clear plastic directly on the soil is the fastest way to warm soil to get a jump on the season. Â Drier soil will be warmer so the plastic will help keep added rain from preventing warm up. The natural heat lower in the earth will combine with any solar radiation you get (even on moderately cloudy days) and be trapped by the plastic. There is no a benefit from using black plastic unless you know you will have direct sunlight … and if you do, you probably don’t have a cold soil issue
