As you work upward and outward after clearing the tree's inner air space, room for the secondary branches and twiggy terminals increases. Your object here is only to lessen interference, without creating gaps in the tree's spread and crown. Gaps are not only unsightly: they expose interior stems to sunscald. Take it easy as you go and stand off frequently to study your progress. Remember, there is no fixed rule for the shape or density of any tree, unless it is this: after you have pruned, your efforts should not, like a "plumber's haircut," be too obvious. A properly pruned tree has an airy, graceful wholeness that persuades the beholder it grew just that way all by itself.

If the tree is too wide or too tall to suit you, or is threatening to become so, do not shear or head it back as you would a hedge. Single out the too long or too high members and lessen them one by one by drop-crotching—that is, cutting back to a fork where the abbreviation will look natural. (This overhead work will perfect your handling of the pole tools.)

Finally, if the tree stands where traffic or mowing machinery must pass, eye it for ample clearance and prune accordingly. Better a few less branches than any bruised ones.

Thus far we have generalized about pruning small deciduous trees. Evergreens call for different treatments, which will be discussed below. Pruning fruit trees, too, has special rules, which appear in a later chapter. Here it would be well to draw some distinctions about the pruning of deciduous species with various habits.

The leafy sucker growths on elm trunks and branches, also called "hairs" or "feathers," are somewhat necessary to these water-loving trees, especially aloft, to keep them from dehydrating. They should be pruned sparingly. But all elms should be watched closely for deadwood, which invites the bark beetles that carry dread Dutch elm disease.

Plane trees are vulnerable to cankerstain, a fungoid disease that is highly infectious, but less so in dead of winter. That is the only time planes should be pruned; and even then, disinfect the tools.

Pin oaks put out laterals so closely spaced sometimes as to look overgrown, but these should be thinned with much caution. This tree's branches support each other under loads of rain and snow.