Aerification of golf course putting greens is the most disruptive maintenance activity, but it is also one of the most important. Proper aerification creates a healthy growing environment for turfgrass. That healthy growing environment is very important when we consider the stresses that a putting green is subjected to: traffic, low mowing heights, nematodes, diseases, low light conditions -- the list is extensive. But putting greens are also the most important area of any golf course. Turfgrass managers should do everything they can to create a healthy growing environment for putting green turf.
I have written about the importance of filling core aeration holes with sand, and this video from Washington State University shows how water does NOT easily enter aeration holes that have collapsed at the surface. Coring holes must be filled with sand to get the desired effect.
Everyone knows that coring is disruptive, but having bad greens is even more disruptive! Having an effective core aeration program is a key to having good greens, and at many of the courses that I see in Asia that have recurring problems with the grass on their greens, we can trace the problems back to a general lack of core aerification, and a subsequent accumulation of organic matter at the putting green surface.
So how much coring is enough? It depends on the course, but I say that at a bare minimum, there must be at least 10% of the putting green surface area removed each year and replaced with clean sand in the holes. Ideally there would be 20% of the green area removed, and if the ownership of a course wants to have good greens, they will find a way to get this done. Chris Hartwiger and Pat O'Brien, agronomists with the United States Golf Association Green Section, recommend 15 to 20% of the green surface area be removed each year. Courses in Asia that remove less than 10% of the green surface area by coring each year tend to have recurring problems with their greens. The exact amount of surface area to remove must be decided on a course-by-course basis, but you can be pretty sure that you need to remove between 10 to 20% of the green surface area annually.
[Update in 2019: I think one can make a more site-specific calculation of how much coring is required. See more recent thoughts about this matter at Core Aerating Putting Greens, Or Not and This One Simple Trick to Consistently Great Greens.]
I would never make an aerification without first determining how much of the green surface area will be affected. The calculations are simple. We know the tine diameter and radius and can calculate the area affected by one core using the formula π * r2. The number of coring holes per unit area can be calculated based on the tine spacing used on the machine; tines on 5 cm x 5 cm spacing will give 400 holes per m2. So as an example, 10 mm diameter tines used to aerify a green on 5 cm x 5 cm spacing will remove 3.1% of the green surface area. Using 12 mm diameter tines on the same spacing will remove 4.5% of the green surface area.
All other factors being equal, the key determinant of recovery time from aerification will be the tine diameter. Larger diameter holes take a longer time to recover. So for efficient aerification, with the least disruption to the golfer, removing as much of the green surface area as possible while still having the fastest possible recovery time, my goal is always to use the closest possible tine spacing and an approriate tine diameter. If you are able to set your aerifiying machine to a 2.5 cm x 2.5 cm spacing, there will be 1600 holes per m2! But keep in mind that it is not the number of holes on the green that cause a disruption to putting quality. It is the time the holes remain open without the grass growing back over them that actually causes a disruption to play.
Here are some tips for effective core aerification of putting greens:
- Ideally you will remove cores from 20% of the green surface area each year.
- Be sure to remove at least 10% of the green surface area by coring.
- Do whatever it takes to fill the holes with sand -- coring holes that are not filled with sand only have a temporary benefit to the putting green quality.
- Because small holes are very difficult to fill with sand (because of bridging of sand particles at the top of the hole), I recommend the use of tines at least 10 mm in diameter -- 12 mm or 14 mm are even better.
- I always try to minimize the tine spacing, making the holes as close together as possible. This is the most efficient way to core aerify while minimizing disturbance to golfers.