Part 1
Transcriber Note
Whole and fractional parts are shown as 2-1/2. Emphasis shown as _Italics_ and =Bold=.
UNITED STATES DEPARTMENT OF AGRICULTURE
=BULLETIN No. 816=
Contribution from the Bureau of Plant Industry
Wm. A. Taylor, Chief
Washington, D. C. [Illustration] January 19, 1920 -------------------------------------------------------
=STREET TREES=
By
=F. L. MULFORD, Horticulturist=
Office of Horticultural and Pomological Investigations
CONTENTS
Page
Importance of Shade Trees 1
Public Control of Street Trees 6
Planning for Trees on City Streets 8
Spacing Trees 9
Conditions for Tree Growth 10
Kinds of Trees Suitable for City Streets 14 Qualities Necessary 14 Trees for Different Regions 16 Trees for Special Purposes 20
Descriptions of Street Trees 20
Culture of Street Trees 43 Selection of Individual Trees 43 Preparation of Holes 44 Planting 45 Pruning 50 Stakes and Guards 51 Later Care 52
Care of Mature Trees 53 Pruning 53 Feeding 55 Spraying 55
WASHINGTON GOVERNMENT PRINTING OFFICE
1920
=BUREAU OF PLANT INDUSTRY.=
William A. Taylor, _Chief_. K. F. Kellerman, _Associate Chief_. James E. Jones, _Assistant to Chief_. J. E. Rockwell, _Officer in Charge of Publications_.
Office of Horticultural and Pomological Investigations.
SCIENTIFIC STAFF.
L. C. Corbett, _Horticulturist in Charge_.
Truck Crop Production Investigations:
J. H. Beattie. F. E. Miller. C. J. Hunn. B. J. McGervey.
Irish Potato Production Investigations:
William Stuart. C. F. Clark. W. C. Edmundson. P. M. Lombard. J. W. Wellington. L. L. Corbett.
Truck Crop Improvement Investigations:
W. W. Tracy. D. N. Shoemaker.
Landscape Gardening and Floriculture Investigations:
F. L. Mulford. W. Van Fleet.
Bulb Culture Investigations:
David Griffiths.
Fruit and Vegetable Utilization Investigations:
J. S. Caldwell. C. A. Magoon. C. W. Culpepper.
Fruit Production Investigations:
H. P. Gould. L. B. Scott. C. F. Kinman. George M. Darrow. E. D. Vosbury.
Grape Production Investigations:
George C. Husmann. Charles Dearing. F. L. Husmann. Elmer Snyder. G. L. Yerkes.
Fruit Breeding and Systematic Investigations in Pomology:
W. F. Wight. Magdalene R. Newman.
Fruit Improvement through Bud Selection:
A. D. Shamel.
Nut Investigations:
C. A. Reed. E. R. Lake.
Fruit and Vegetable Storage Physiology:
L. A. Hawkins. R. C. Wright. J. R. Magness. J. F. Fernald.
Extension Work (in cooperation with States Relations Service):
W. R. Beattie. C. P. Close.
UNITED STATES DEPARTMENT OF AGRICULTURE
Contribution from the Bureau of Plant Industry
WM. A. TAYLOR, Chief
Washington, D. C. [Illustration] January 19, 1920
=STREET TREES.=
By F. L. Mulford, _Horticulturist, Office of Horticultural and Pomological Investigations_.
CONTENTS
Page
Importance of Shade Trees 1
Public Control of Street Trees 6
Planning for Trees on City Streets 8
Spacing Trees 9
Conditions for Tree Growth 10
Kinds of Trees Suitable for City Streets 14
Qualities Necessary 14
Trees for Different Regions 16
Trees for Special Purposes 20
Descriptions of Street Trees 20
Culture of Street Trees 43
Selection of Individual Trees 43
Preparation of Holes 44
Planting 45
Pruning 50
Stakes and Guards 51
Later Care 52
Care of Mature Trees 53
Pruning 53
Feeding 55
Spraying 55
IMPORTANCE OF SHADE TREES.
The comfort to be derived from shade trees has long been recognized. The early settlers of this country saved fine trees about their homes, on the village greens, along the country roads, and in the fields. Later, as villages grew, the householders planted trees adjoining their properties, and the result has been the beautiful elm-shaded villages of New England, the maple-shaded towns of New York and the Ohio Valley, and the oak-shaded streets of the Southeastern States. (Fig. 1.)
With time, the villages and towns became cities, and the woodlands were largely destroyed. Conditions for tree growth were less favorable in the cities, and nurseries had to be depended upon for planting material. With these changed conditions the native trees of a region became less dominant in the city planting and were largely replaced by those trees listed in nursery catalogues which took the fancy of each property owner along the street. (Fig. 2.) The quickest growing trees were considered first, and as some of these made a big showing the first few years and were easily transplanted, they have become the dominating trees in street planting from the Atlantic to the Pacific and from the Great Lakes to the Gulf of Mexico. (Figs. 2, 10, and 13.) A few have planted better and more lasting trees (figs. 1, 3, and 4); but the tree growth on the streets of the average town or city is ragged and unkempt in appearance, while that of the suburb or small village is not much better unless the planting has been done under municipal control and the plantings on a street have been confined to a single kind of tree.
The advent of such civilizing agencies as the telegraph, the telephone, the electric light, and the trolley car have added each its share toward the mutilation or destruction of the good trees that were in existence at the time of their coming. Faulty methods of pruning also have caused much disfigurement and ruin. (Figs. 5 and 21.) To this mutilation has been added the unnecessary destruction of many trees in centers of business (fig. 6), because they excluded a little daylight, or made a store less prominent, or were somewhat in the way of using the sidewalk for merchandise.
In spite of all these troubles tree planting has continued because people love trees, enjoy well-shaded streets, and are willing to make efforts to get them. The trees on well-shaded streets are not only pleasing, but also contribute toward the health of the community by transpiring moisture into the atmosphere and by producing a restful effect on eyes and nerves. Red, especially, is known to have an exciting effect on human beings, and where city streets are well-shaded it makes less prominent those colors that might otherwise prevail and offend.
Good shade is so appreciated that its presence adds a value to adjoining properties. Real-estate men recognize this factor and plant shade trees as early as practicable on land which they develop. That the beauty of a city is improved by good street trees is becoming recognized more and more and is finding expression in the desire of garden clubs, civic improvement associations, and boards of trade for information on this subject.
Success in planting street trees can be attained only by planning and controlling the planting as a whole, by selecting the most suitable varieties, by securing trees in the best condition and planting them properly, and by giving the necessary later care.
While towns were small, conditions for tree growth favorable, and woodlands plenty, so that native trees were easily obtained and started, the practice of each householder planting his own trees as he saw fit gave good results. As towns became larger and impervious pavements took the place of earth roads, the conditions for tree growth became more severe and the results from the individual planting of trees less uniform. In large cities the conditions to be met are so extreme that it has become practically impossible for the average householder to grow street trees successfully, or to do so only at excessive cost. Then, too, a lineman in a few minutes often undoes what the individual has achieved with care and years of patient waiting (see fig. 5). The trees and the lines are both needed by the public, but when provided by individual initiative at private expense, but trimmed for the benefit of electric lines by employees of corporations intent on maintaining service at the least cost, the trees suffer unduly.
In order to have good shade trees at a reasonable cost which receive timely and efficient attention, with the effective control of wire lines, the care of the trees needs to be vested in some adequate authority.
PUBLIC CONTROL OF STREET TREES.
Providing shade on city streets is as much a municipal function as providing lights or sidewalks and should, therefore, be cared for by public officials. All street trees should be directly under the care of duly appointed officers, who should be responsible for their planting and care, as well as for their pruning or removal. Negative control by requiring permits for planting, pruning, and removal is little better than no control.
The officials in charge should have the necessary authority and should be required to initiate and carry forward planting and all other needed work connected with the establishment and maintenance of street trees. Probably the most satisfactory way of securing supervision is through an unpaid commission of three or five members, which in turn employs an executive officer. In a small place a commission of three persons may be best, one being appointed every 2 years for a 6-year term. In large places five members may be better, and the ideal term would be 10 years. A compromise would be a 5-year term, a new member being appointed each year. The great need of long-term appointees is that it takes two or three years for a member of such a board or commission to see and realize the things needed to be done and the policies that should be carried out. Because it takes a long time to get results in growing street trees, the policies should be as nearly continuous as possible and the terms of the members long enough to insure a majority of experienced persons on the board at all times.
The method of appointing the commissioners is not so important as that each shall be selected from the territory as a whole rather than from a part of it. In some places where the term of service is 10 years, each one's successor is appointed by the remaining commissioners, subject to confirmation by the court. Where this is done a member is not permitted to succeed himself. In other places the commission is appointed by the court; in others, it is elected by the city legislative body or is appointed by the mayor subject to the approval of the legislative body. The important point is to keep the administration as nearly as possible on a purely business basis.
A good board can accomplish nothing without liberal funds. There are two methods of providing these: (1) By an appropriation from the general tax levy and (2) by direct assessment against the properties, collectible with the other taxes. If the funds are provided by appropriation, a fixed minimum, expressed in millage of the tax rate, should be provided in the organization of the commission. This minimum should be such that a fair amount of maintenance work can be done when no other funds are available. Councils that appropriate money sometimes hamper boards by withholding appropriations. Work of the nature of tree planting should not be permitted to suffer or be lost by a year's neglect. The fund provided by this minimum amount should not be so large that regular additional appropriations will not be needed to carry on the work properly, as this will give a desirable point of contact of the commission or board with the ordinary channels of expressing public sentiment in the district interested. The minimum appropriation mandatory should be sufficient to prevent injury from lack of care of work already begun. A period of minimum care and attention while a board and the people or their representatives are coming to a new understanding of one another's position is not necessarily a detriment, provided a reasonable maintenance has been possible in the interim, but without such care the results are ruinous and work would better not be started than be undertaken with the possibility of such a period of neglect occurring.
It is probably desirable to assess the cost of tree planting against the adjacent property owners at a proportional cost per front foot and to provide for maintenance out of a general fund. Boulevards and other unusual developments are sometimes maintained with satisfactory results by regular assessments against the abutting properties.
After a proper governing board is provided, the securing of a competent executive is a matter of ordinary business procedure. It is usually desirable that he shall be not only a good executive but also a man with a knowledge of trees and trained in their care, so that he may be a competent adviser of the board as well as its executive.
PLANNING FOR TREES ON CITY STREETS.
With the help of one who knows trees and the local conditions to be met, the town should be studied and a suitable kind of tree selected for each street or for a large portion of a street (figs. 1 and 3), and as conditions warrant the plan should be carried out as outlined. Mixed plantings of different sorts of trees (figs. 2 and 7) are not as pleasing and effective as the use of a single species for considerable distances. The use of only one or two kinds for a whole town is likely to be monotonous, and it is also undesirable because the variety most used may become subject to serious disease or insect attacks. The species and varieties of trees suitable for city planting are few enough, if all are used, so an endeavor should be made to include as many different kinds as practicable, assigning one variety for a long stretch of street unless there is a marked change in its character, in which case a change of trees would be warranted.
Where trees are already on a street, the problem of planning for the future is frequently much complicated, especially if there are several kinds in good condition. Where there is but one good kind, gaps can be replanted with young trees of that sort. If there are poor trees of a good variety or trees of a poor or short-lived variety it would be advisable to remove these and do all the replanting at one time, so as to have the trees on the street as nearly uniform as possible. Where there are several good varieties in good condition the sensible thing is to care for the trees that are there and then, after careful study, decide on one variety for all future plantings on that street.
SPACING TREES.
A common fault in all street planting is to put the trees too near together. (Fig. 8.) This is more evident where the work has been done by the abutting property owners than by municipalities.
After trees are started and have attained some size it is extremely difficult to get them removed, even where the good of the remaining trees demands it. The removal of a fairly good tree merely because it is short lived in order to make room for a good one that will be permanent does not appeal to the average citizen. Where trees which have been planted by the property holder come under city control a strong feeling of proprietorship still remains, which is outraged by the suggestion of the removal of even poor trees. Where all the work is under city control good work is often hampered by a strong public sentiment against the removal of trees, even though they are poor or crowding.
Because of this difficulty it is extremely important that young trees be planted farther apart than at that time seems reasonable. If they are planted as far apart as is proper for mature trees the distance will be so great as to make planting seem a joke. If they are planted half the distance apart they should be when mature, good results would follow if the intermediate trees were removed when they nearly touch those to be left. As the intermediate trees would probably not be removed, or not until too late for the good of the remaining ones, planting had better be sufficiently far apart in the beginning to avoid the necessity of later removals. In the beginning the trees will be too far apart and when mature too close together, but it seems to be the alternative imposed by a misguided public opinion.
There is scarcely a community that would permit the removal of interplanted trees from a street of fine elms, oaks, or other worthy varieties without a protest that would be the almost sure political death of the administrative authorities responsible, no matter how great the need or how much expert support they might have. If short-lived intermediate trees were used they would not be likely to be taken out before they died, and they probably would not die before they had irreparably injured the permanent trees. The removal of surplus or interplanted trees can be made with least shock to the community by gradually narrowing the tree tops by severe pruning from year to year on the sides next the permanent trees until finally they are so narrow they may be removed and leave only small openings between the permanent trees. Even this method will not materially lessen the public protest at the final removal.
A common practice is to set street trees 35 feet apart. If it were practicable to remove one-half the trees at the proper time this would be a good distance, but in the eastern half of the United States and on the Pacific slope 50 feet apart is close enough for most varieties, and for the larger growing trees 60 to 70 feet would be better.
CONDITIONS FOR TREE GROWTH.
In order to grow, trees must have a soil of suitable texture, in proper mechanical condition, that contains sufficient available mineral elements and plenty of organic matter, and, last but not least, a constant supply of moisture and air. In addition to these there must be in active growth in the soil many forms of organic life that are in various ways preparing the material in the soil for the use of the larger plants. Not only must these things be present, but others that are deleterious must be absent, whether the substance is hurtful in itself or whether it is an excess of one that is otherwise beneficial.
Above the soil three things must be present--air, sunlight, and moisture--and, as in the soil, harmful things must be absent in order to have success. Among the deleterious substances are sulphur and other fumes and soot and other products from incomplete combustion.
Some of the more obvious things with which a city tree has to contend are: Water-tight pavements, both on the sidewalk and street, that prevent the admission of air and water; the removal of the topsoil in street grading, thus forcing the tree to exist on the good soil provided in the hole; careless digging near the tree for gas, water, and electric service, and especially for the placing of curb-stones; the saturation of the soil with illuminating or sewer gas from defective pipes (fig. 9); the pouring of salt water from ice-cream freezers into gutters, where it may find its way into the soil near tree roots; the gnawing of the trunks by horses; and the cutting of the tops by linemen and tree trimmers.
Because of the uncongenial conditions for the growth of trees on city streets comparatively few kinds are satisfactory for such use. Among those available are some that will grow under extremely trying conditions. Kinds can be found that will thrive wherever it is suitable for human beings to live. If it is impossible to grow trees on a street, as a health measure that street should be closed for human use until conditions are so improved that it will support trees.
More kinds will thrive under suburban conditions where only a small portion of the roadway is covered by an impervious coating, where the parking spaces are liberal, and where the street is lined with open lawns than under the conditions in a city, where the street is covered with a water and air proof coating and the sidewalks with an impervious material, where parking spaces are limited, and where adjoining lawn areas are small or lacking. By a careful selection of kinds, all conditions in a city can be met. In some places bad conditions could have been improved greatly by a little forethought; in others, such conditions can be bettered. These details, like many other matters connected with city planning, have been ignored, but should be considered immediately, especially by villages and small cities. Figure 6 shows how an opportunity for creating a beauty spot has been lost sight of, while figure 10 shows how a city has utilized less ground to increase the comfort and attractiveness of its business center.