Coring three times a year is recommended when ...
When a lot of nitrogen is applied relative to plant demand, I guess.
The article Creeping bentgrass surface properties following aerification by Hubbard et al. reports the results of an experiment looking at various aerification treatments, tine diameters, and tine spacings on a `Crenshaw’ creeping bentgrass green at Clemson, South Carolina.
The authors end with this:
Overall, this study would support a recommended aerification program for bentgrass greens in the transition zone to include two spring [hollow-tine aerification] applications with 1.2 cm tines [0.5 inch] at 5.1 x 5.1 cm [2 inch x 2 inch] or 0.9 cm tines [0.375 inch] at 3.8 x 3.4 cm [1.5 x 1.4 inch] (March and May), monthly [solid-tine aerification] during the summer, and a fall [hollow-tine aerification] application with 1.2 cm tines at 5.1 x 5.1 cm.
I read that, and I read it again, and I muttered “wow,” or something to that effect, and then I looked at the Materials and Methods section of the article. The annual N rate on this green was 34.2 g N/m2 (6.8 lbs N/1,000 ft2). The green was established fourteen years prior to the start of this experiment on a green “originally built to USGA specifications.”
![This green [this is not the green in the experiment] was cored with 1.2 cm diameter tines but it won't get this treatment three times per year---the coring amount is adjusted based on OM246 test results and putting green performance (playability).](/post/coring-three-times-a-year-is-recommended-when/featured_hua3a14226fbc55da7aaf6bb20c4de28f0_361744_b442647e690bdb3d6e8f4aa7f736b8b3.webp)
That’s a lot more N than I would expect creeping bentgrass to use in such a climate. I used to suggest a monthly maximum N of 3 g/m2 when the temperature-based turfgrass growth potential (GP) was 1. Now I suggest a monthly maximum of 2—for creeping bentgrass greens, at least. Running the GP model for temperature data at Clemson, I get an annual N estimate of 13 g/m2 using my current maximum of 2 g, and I get 19.5 g/m2 using my previous maximum of 3 g. This green was getting 34.2!
One way I could try to interpret these results, I guess, is to assume the grass grows according the rate of N applied, and then to consider how much coring (hollow-tine aerification) treatment might be required if the grass grew at $\frac{13}{34.2} = 38$% the rate it did in this experiment. In that case, with about a 62% reduction in growth, would the coring requirement go down by a similar amount? Perhaps.
I recommend checking the total organic material (OM246) on your greens, noting how it changes over time in response to the work that you’ve done, and from that developing a site-specific plant for the amount of hollow-tine aerification and sand topdressing required for the greens you manage.