Common groundsel is an important weed of strawberry and other horticultural crops. Few herbicides are registered for common groundsel control in such crops, and understanding and predicting the timing and extent of common groundsel emergence might facilitate its management. We developed simple emergence models on the basis of soil thermal time and soil hydrothermal time and validate them with the use of field-derived data from Minnesota and Ohio. Soil thermal time did not predict the timing and extent of seedling emergence as well as hydrothermal time. Soil hydrothermal time, adjusted for shading effects caused by straw mulch in strawberry, greatly improved the accuracy of seedling emergence predictions. Although common groundsel generally emerges from sites at or near the soil surface, the hydrothermal model better predicts emergence when using hydrothermal time at 5 cm rather than 0.005 cm, probably because of the volatility of soil temperature and water potential near the soil surface.