I have been preparing some ideas for publication on training fruit trees and have encountered some confusion around tree form terms. The terms delayed open center and modified central leader are often used interchangeably. I have typically used them interchangeably to indicate a tree that has an open center form, but with the branches evenly spaced, and a shortened, diversified top. The top, ideally at least, is decreased in vigor by 3 to 4 fairly tall, vigorous and reasonably upright branches (45 degrees or less at trunk to branch angle). The center portion is small, branching, and small, like a small centerpiece.
Perhaps the more common usage though is to indicate an open center tree that has branches well spaced along the trunk instead of coming out all at one point, or randomly. The central leader is cut out and it is grown as an open center tree with no dominant leader.
I started to wonder if these two terms are really synonymous and maybe modified central leader better describes what I like to do. The only way the term Modified Central Leader refers to an open center tree is that the top branch is equal in vigor to the other branches and is laid off to the side. So, it is really just an open center tree with more deliberately placed branches, and the central leader is just cut out.
Modified Central Leader on the other hand, better applies to the way I do it, where the central leader is still there, but it is largely subordinated, or at least weakened by the tall vigorous and relatively upright limbs, or as I said, it’s like an open center tree with a centerpiece. While open center trees are employed in this part of the country, they are especially prone to sunburn due to the intense sun reaching the center and hitting the angled branch surfaces. They burn easily for the same reason the tops of our noses burn easily. Having a bit of growth in the center of the tree, while partially negating the opening of the tree to light, which is one of the main reasons for growing open center trees in the first place, partially shades the center and protects from sun burn. I usually top the center at about 18 inches and let it fork into two or three mini tops that are shortened yearly.
Does anyone use these terms separately, or are you aware of any sources that discuss them separately? Any other thoughts welcome. Personally, I’m inclined to start using the terms separately to refer to these two forms and have to wonder if they were not originally referring to different systems. I always use a form something like one of these for large trees, because it is strong and once established, never requires the removal of larger branches that begin to crowd as the tree gets older.