As a part of my spring lawn care I power raked detached, scarified and then overseeded my lawn. In this video I share my results now that it is 2 months later. To be honest 90% of the results that I had were right when I originally dethatched. My results may be skewed due to the weather conditions that we had this year but it will be interesting if the soap makes a difference.
The thought process of shampooing or washing the lawn is to attempt to wash away a waxy layer that has built up on the surface of the dirt. Washing away this layer should allow water to penetrate down into the soil easier and make it easier for water to get to the roots of the grass. I used Johnsons Baby shampoo and used 5oz per 1,000 sq feet. The area I treated was a total of 2,000 square feet so I used a total of 10oz of shampoo.
I understand the thought process behind washing or shampooing the lawn but I am very curious to see if it will actually work. That being said, the combination of dethatching, washing, and then in the future aerating the lawn I do believe it will make the yard much better.