There are many things you can do to rejuvenate, clean up and make healthy your overgrown shrubs and small trees. Thinning is the most important technique to learn. Judicious thinning can invigorate a plant, accentuate its character or make a dense, heavily leafed plant look lighter and more beautiful. Even the largest, most oppressive looking shrub can be made friendlier with the proper pruning.
Thinning means lightly pruning without making heading cuts -- like those found on decapitated Mulberries. A thinning cut takes a branch back to its point of origin, usually to where it forks from a larger branch. A heading cut, by comparison, gets done at an arbitrary point on a branch. That point may be ten inches or ten feet from a fork. Tree topping, as in the case of our brutally assaulted Mulberry, is an example of numerous heading cuts made across a tree's canopy. This stubbing destroys a plants' character. Thinning cuts, however retain a plants' natural form.
Many people avoid thinning, though, because they don't know where to start. It is easier, they say, to pick a point in the canopy and head back all branches to that same size. Look at the tangled branches in the first illustration. Where does one begin? After eliminating any branches that physically touch and rub against each other, try removing 20 to 25 per cent of all interior branches. The best approach is to strike a rough balance between open space and closed space across thewidth of the plant. Think of this as a balance between dark and light. Start with the densest, most congested part of the interior and remove small branches until you can see through the interior. Continue on until the whole plant displays a somewhat uniform play of light. Take your time.
Don't worry if you produce some awkward gaps here and there. Use green twine or plastic garden tape to pull nearby branches toward these gaps. Step back from your work as you go. You can't develop any sense of what you're doing unless you back up ten to fifteen feet. Finish up with a strong jet spray of water to knock down litter and debris produced while pruning. If you really want to make your shrubs sing, and not just hum, consider eliminating lower branches from ground level to a height of six inches or so. Not only will raking and maintenance be easier, you'll create a dark shadow band and a sense of lightness at the same time. Shrubs up against a solid fence? Eliminate some or all fence facing branches to lighten things up even more.
There are cases, of course, in which you do not desire any thinning. Hedges used for privacy and screening must be as dense as possible. These include privet, photinia, xylosma and oleander, just to name a few. Overgrown shrubs like these are best headed back several feet on the top and on the side. Water well afterward and fertilize with a weak solution in two or three weeks. Although most new growth will appear at the top and on the sides, you should get some new interior growth as well. Keep top growth and side growth in check by pruning lightly over the next several months, but allow all interior growth to fill in as much as possible. Pruning the top, sides and interior in this manner will result in a very dense hedge by the end of summer. I prefer, by the way, to do my most drastic pruning when there is no heat spell going on. It also helps to water first.
Uniform thinning is also unwanted on certain other trees and shrubs. Those trees with a stratified branching pattern, such as some Japanese maples, Tupelo (Nyssa sylvatica), Hollywood Juniper and Monterey Cypress are all examples of plants with a multi-layered, horizontally based branching pattern. Emphasize this characteristic by pruning out strongly vertical branches and by tying down, with tapes or weights, branches that exhibit good lateral growth. You'll have a very distinctive plant in just a few years if you prune consistently.
Thinning is also impractical, in the long run, for the few shrubs and trees that are naturally congested. These include redwood hedges, Olive trees, African Sumac (Rhus lancea) and Carob trees (Ceratonia siliqua). Each cut on these plants result in several new shoots arisingfrom the point just pruned. The only real solution is to treat each cut with napthaleneacetic acid (NAA). This growth inhibitor is sold in many forms, including spray cans. One trade name is Maintain. It's available in larger orchard supply stores. Buy a can and experiment -- you'll find it keeps congested plants cleaner for a longer time than any amount of hand pruning can do.
The last point to emphasize about thinning is difficult to describe. Most trees have a fairly straight trunk for five or six feet and then three or four main branches lifting skyward after that -- a classic vase shape. Too many people, for some unknown reason, make bare these main branches. Don't do that. Keep some smaller growth along large branches or the tree will look very unnatural.
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