This question arrived recently to my inbox. I paraphrase:
“Sir my greens are hard, the ball bounces and goes beyond the hole. Please give me recommendations on the steps taken to keep green soft. I have done vertidrain with solid tines but the effect is temporary. Please send suggestions.”
I’ve thought about this for a lot of climates, grasses, and soils, and I’m pretty sure this is a good way to handle this situation.
To make greens softer
The idea is to make gradual increases in organic matter near the soil surface until the desired surface hardness is achieved. To accomplish this, I want to grow more grass, and remove less organic matter. The specific things to do are to make the grass grow more, which can be done by increasing the nitrogen (N) fertilizer rate, and adding more water. I think 20% increments of increase are reasonable as a starting point, and one can evaluate the turfgrass response and make further adjustments. Also, I would do less verticutting, less sand topdressing, and less core aerification. Again, I think 20% increments are a reasonable first guess of how much to change things. If you do this for a while, I expect the surfaces will become softer.
To make greens harder
To create a harder surface, one does the opposite of the above. One wants to decrease the organic matter near the surface. To do that, I want to the grass to grow less, and I want to remove (or dilute) more organic matter. I would apply less N and water – that will make the grass grow less. I would add more sand and do more coring – that will remove organic matter. If I had no other idea, I would change all of those by 20% as a starting point.
What I’ve written above applies to sand rootzones. For turf growing on soil rootzones, the expected outcome is a bit different. See this video from Dan Dinelli:
When growing on soil, then I expect the surfaces to be harder than if on sand, assuming the soil is allowed to dry. So if you have turf growing in relatively dry soil, and want to make the surface softer, I suggest adding more water and more sand.