45° F? Chilly feet for the seedlings indeed. Getting the sheet mulch down will help. Paper mulch around the seedling stems will help. Still, there’s good reason to have Memorial Day as our default day for planting, isn’t there?

Measuring soil temperature is a good exercise for me, because it keeps the idea of soil as a living system in the forefront of my mind. Soil isn’t just there. It’s ever responsive to changing conditions, including air temperature.