An article writen by USGA agronomists suggested that on mature greens the area impacted each year should be about 15%-20%. This is based on controlling organic matter buildup and intended as a general guide as there are many variable factors. If there is an existing thatch layer these figures will have to be increased to address the problem.
The table below shows a comparison between Coring and Graden'ing for impacting surface area for thatch removal. The Graden blades have been accurately measured and are wider than 1, 2 and 3 mm, the figures are based on the actual widths of the blades. We have also measured the inside diameter of the bottom of new hollow tines (plug size is determined by this) which is far less than the specified tine size, the area impacted will increase as tines wear. Results are from largest tines tested and will vary with different manufacturers.