Avoid aerifying a wet soil, as it is messy and leads to further compaction of the soil as well. If the soil sticks to your shoes or if the soil core sample you take sticks to your probe, you should wait until it dries out some before starting when to dethatch lawn the job. If aerifying in the summer during a droughty period, monitor your irrigation as an aerified turf will tend to dry out quicker than before the aerification process. Compacted soil can also contribute to the accumulation of thatch.