What month do you dethatch?
The best time to dethatch your lawn is when it's actively growing and the soil is moderately moist. For cool-season grasses, that's early spring or early fall. For warm-season grasses, dethatch in late spring through early summer (after the second mowing). That's when your grass is growing most vigorously.
When should you not dethatch your lawn?
Dethatching causes a lot of damage to your grass and should be done at a time when the grass is growing so it can fix the damage before the next dormant period. Warm-season grass can be dethatched in late spring or early summer after it starts to grow. It is best not to do it in the middle or late of summer.