Developing Shrubs into Trees

As the horticultural supervisor for a fairly large institution, I work with several different crews, each of which has it?s own realm of responsibilities. One of those crews is a group of highly trained and motivated professionals that is responsible for maintaining the trees on campus. We call them, simply enough, our tree crew. Now, it?s obvious to all that the ash, mulberry, mesquites and locusts on campus are all in their realm of responsibility. But I sometimes find myself facing a dilemma I?ve never had before; I?ll be standing on campus, looking at a particular plant, and asking myself the question, ?Is that a shrub or a tree??
 
The answer to my above question is yes. The plant usually can be either, and it?s up to me as the caretaker to decide which it is. Now this is more than merely a debate about language and definition. It is a matter of determining the developmental approach to take for that plant to best fulfill its role in the landscape.
 
So what exactly am I talking about here? The point I?m trying to make is that many of the ?shrubs? in our landscapes would more fully realize their potential if they were developed and maintained as trees. They are woody, long lived, trunk-developing perennials, which is, by the way, I think a good definition for a tree. In fact, after having arrived at that definition on my own, I looked it up in the 1947 edition of Funk and Wagnall?s ?New? College Standard Dictionary, (ok, so I?m a bit behind the times in some respects), and I was relieved to discover my definition closely matched theirs. The only differences are that they referred to it as ?having a single self-supporting trunk?, a point I?d be willing to debate, and that they range ?from about ten feet to as high as three hundred feet?.
 
About ten feet, huh? Surely, the dwarf peach trees that I?ve worked on over the years, which max out at about 6 or 7 foot tall, are indeed trees. So now I?ve managed to further minimize the height a plant must reach to achieve tree status. Or should the definition be based on species as well as size? Should we take growth habits into account as well?
 
The answer is up to us as the caretakers. We can develop shrubs into trees, and maintain our trees as shrubs, some of them anyway, if we so choose. And many of the plants that are now being kept as shrubs would do well if their care regimen were to change to allow them to develop as small trees.
 
The plants that I?m talking about here include, but are not limited to, such species as Photinia x frasieri (frasiers photinia), Pittosporum tobira (mock orange), Myrtus boetica (twisted myrtle), Myrtus communis ?Compacta? (dwarf myrtle), Xylosma congestum (xylosma), Euonymous japonica (euonymus), and Nerium oleander (oleander). Each of these species are usually maintained as shrubs, often in hedges, and often sheared. In fact, these maintenance practices are usually detrimental to the health and aesthetic qualities of these plants. The shearing of the large leaved members of this group results in ragged, marred and brown leaf edges, and others, such as the twisted myrtle, lose their unique and beautiful natural form. In the case of the oft-maligned oleander, the pruning often seems timed to best remove the flower show.
 
These plants often perform and show best if they are developed into small trees, assuming space and design characteristics allow for it. This is especially true if one takes into account the limited yard space that most single-family homes and apartments complexes have. A well pruned and developed photinia for example, maxing out at 15 to 20 feet in height, can be the perfect focal point and visual anchor for a small landscape, assuming one is willing to provide for it?s nutritional (read as chelated iron) needs.
 
The developmental regimen one must undertake to develop these specimens as trees are similar in many respects to ?regular? tree care, with just a few differences. First off, throw lines and rigging devices are likely to not be needed. Much of the work, especially at first, is likely to be performed on your belly, for one of the first steps is to choose which of the lower trunks and laterals are to be maintained and developed into permanent wood, and which are only temporary. When choosing, select well-positioned and divergent branches and stems that are appropriately spaced and free of included bark (weak crotches). Because these trees are smaller in stature than our oaks and pines, a smaller vertical branch spacing of six to twelve inches is sufficient.
 
Most of the standards of good tree care remain in place, unchanged. Never remove more than 25% of the plants foliage in a year, with less often being better. Lift the tree slowly, retaining some lower branches temporarily to shade and strengthen the trunk. Remove crossing, rubbing, diseased and damaged branches. Strive for appropriate radial and vertical branch positioning with good angles of attachment. Make cuts at laterals at least one-third the diameter of the branch being cut, or take the branch all the way off at the point of attachment, leaving the branch collar (the swell of tissue on the trunk where the branch begins) intact.
 
Not all of the large shrubs in our landscapes would best be maintained as trees, but I think we might be missing some wonderful opportunities here. I?ve admired twenty-foot oleanders, pendulous under the weight of their own flowers. I know of photinias strong and woody, with their trunks exposed to show magnificent and wild structure. I?ve walked beneath a long archway of euonymous and mock orange, raised into small trees on either side of a walk, pleached together overhead, and filling the air with wafts of sweet fragrance. I?ve stood spell bound by the flirtations of delicate and incredible butterflies as they?whoops, I?m getting carried away again.
 
You get the idea.