

What is the Minimum Length I Can Remove to "Top" a Podocarpus
Hi all. About a year ago I had a series of mature 24 gallon podocarpus trees planted behind my house. They've really gained some great height since then, but still haven't filled in in the center very much (where you see light in the photo). I've called around and spoke with a few gardeners in my area, and all of them have suggested "topping" or "pinching" the trees by removing material from the top to encourage them to fill in.
Unfortunately, each of them have seemed to suggest a different amount of material that must be removed on the top to accomplish this. AI seems to feel that I would only need to remove as little as 1 to 2 in from the top of the trees to break the "apical dominance" and to encourage them to fill in. Gardner #1 (an arborist) disagreed with this and felt that 6 in off the top would be necessary to encourage the desired thickness. Gardener #2 felt that 6 in would do nothing, and that I need to remove a minimum of 2 to 3 ft from the tops of the trees to encourage thickness.
At this point, I'm not sure who or what to believe. I do know that I hate the idea of removing 3 ft from the top of these beautiful trees, and it would dramatically set back the vertical privacy that I've gained from them. That said, if it's an absolute must to get them to fill in and close these gaps I'll do it. Do you guys have any experience with this or thoughts on the minimum amount of height removal necessary to encourage them to fill in?