About a year ago I posted my thoughts about the nursery production practice of heading young trees (“whips”) to stimulate lateral branching or columnar form or whatever. (You can find this original column here.) A healthy discussion ensued, much of which revolved around the need for appropriate follow-up pruning to ensure the development of a stable crown structure of headed trees.
Fast forward to last month, where a column I wrote for NPM (Nursery Production and Management) magazine hit the web. And then the fan.
I made some people very unhappy with this article. I had a lengthy and productive conversation with one such person last week, during which we agreed on many things, including (1) trees that are headed develop multiple leaders; (2) multiple leaders, however they’re created, need to be thinned to one central leader; and (3) uncontrolled multiple leaders can create hazardous conditions. The bottom line, from a nursery production perspective, is that headed trees require regular pruning to create and maintain natural, structurally sound crowns.
And here’s my problem: how many homeowners are going to perform this regular pruning? Furthermore, how many homeowners KNOW how to perform corrective pruning? We all know that number is going to be abysmally small. Even for those situations where competent arborists could do this regular pruning, how many communities budget for this activity?
More troubling for me as a scientist is the lack of peer-reviewed scientific papers on this practice. Though there are numerous papers documenting the effects of pruning, I can’t find any that specifically look at the long-term effect of heading trees during nursery production. You’ve heard all of us GP’s say it before – unless you can show us the data in a published and peer-reviewed format, we can’t regard anecdotes as anything but.
The nursery industry has invested a lot of time and money in a practice that leads to problems for which no one will claim responsibility. Production nurseries wash their hands of the issue once the trees leave their facility. Many retail nurseries don’t perform the necessary follow up pruning while the trees are in their care (do any retail nurseries do this? Are they aware of the problem?). Homeowners don’t receive information or training on how or why to perform corrective pruning.
What I’d really like to see the nursery production industry focus on is consumer education. The metamorphosis of a sapling into a maturing tree is a wondrous thing. Rather than interfere with the process, we need to cultivate patience as well as a respect for tree physiology.