Hi Lance,

Generally, the best time to dethatch is mid-late spring or early fall. Please see the link and the excerpt below for more helpful information when making decisions concerning your lawncare and any thatch issues.

Plant Talk Publication 1520:

https://planttalk.colostate.edu/topics/lawns/1520-thatch/

From CSU-Extension Fact Sheet 7.202

“Thatch is a tight, brown, spongy, organic layer of both living and dead grass roots and stems that accumulates above the soil surface. The interactions among environmental conditions, soil conditions and management practices (irrigation, mowing, fertilization) influence the rate and extent of thatch accumulation. Thatch tends to be a problem on Kentucky bluegrass, bentgrass and fine fescue lawns. It is rarely a problem with tall fescue, wheatgrass, bromegrass or buffalograss. Grass clippings do not contribute to thatch accumulation and should be returned to the lawn during mowing to recycle the nutrients they contain.

Measure thatch buildup by removing a small piece of turf, including the underlying soil. Try to slow buildup when the thatch layer exceeds 1/2 inch in thickness. The thickness can increase quickly beyond this point, making it difficult to control later. As the thatch layer thickens, it becomes the main rooting medium for the grass. This predisposes the turf to drought stress or winter kill and increases the possibility for insect, disease and weed problems. Also, fertilizers and pesticides applied to a thatchy lawn work less effectively.

Power Raking

This method of thatch removal has been used for years. Light (shallow) power raking may be beneficial if done often. Deep power raking of a thatchy lawn can be damaging, and often removes a substantial portion of the living turf.
Used properly, power raking of wet, matted turf can speed spring green-up by letting air move into the root zone and warm the turf.

Compost the thatch and organic material to kill any living grass before it’s used as a mulch or soil amendment.”