in regions 3, 5, and 13; live in region 2; but are seldom grown
satisfactorily close to the Pacific coast. They can be used effectively
for formal plantings along some streets, park drives, or in liberal
central parking spaces in boulevards, but they are not useful as a
substitute for shade trees. They should have then leaves and damaged roots
cut off in transplanting and should be set about 3 feet deep in their new
location.
The Carolina palmetto[63] is a native of and useful in regions 12 and 13,
where it sometimes attains a height of 60 or 80 feet. It will thrive in
regions 3 and 5, but is used less there.
[63] _Inodes palmetto_ (Walt.) Cook.
The Texas palmetto[64] is especially valuable for southern Texas, where it
is indigenous, and it is likely to succeed generally in regions 3, 5, and
12. It grows to a height of 40 feet and in appearance is quite distinct
from the Carolina palmetto, the leaf segments being much broader and less
drooping.[65]
[64] _Inodes texana_ Cook.
[65] The Texas palmetto. _In_ Jour. Heredity, v. 8, no. 3, p. 123, pl.
1917.
[Illustration: P18989HP
Fig. 27.--A formal planting on a city street. Palms with interplantings.
Redlands, Calif., in midsummer.]
The Victoria palmetto[66] is another hardy species, probably a native of
Mexico, but grown for many years at Victoria, Tex. It is similar to the
native Texas species and worthy of general planting in the same region.
A feature of this species is that the persistent leaf bases remain alive
and green for many years instead of turning yellow or brown, as in the
Carolina palmetto.
[66] Cook, O. F. A new ornamental palmetto in southern Texas. _In_ U. S.
Dept. Agr., Bur. Plant Indus. Cir. 113, p. 11-14. 1913.
WASHINGTONIA PALM.
Washingtonia palms are a very conspicuous feature of street and
ornamental planting in southern California. Two species are represented,
_Washingtonia filifera_ Wendland and _W. robusta_ Wendland. The first is
a native of the canyons and barren slopes that surround the Coachella
Valley of southern California, while the other species probably was
brought by way of the Isthmus of Panama from the region of San Jose del
Cabo, the extremity of Lower California, in the early days of travel.
The name _robusta_ alludes to the fact that this species grows much more
rapidly in height than _W. filifera_, though the trunk is more slender.
Both species are hardy and thrive well through regions 2, 3, and 5, and
also in regions 12 and 13. _Washingtonia robusta_ requires less heat than
_W. filifera_, but both will endure several degrees of frost. Even in
California _Washingtonia robusta_ is distinctly preferable for localities
near the coast. In the vicinity of San Diego the leaves of _Washingtonia
filifera_ become badly infested with a parasitic fungus that does not
attack _Washingtonia robusta_.
OTHER HARDY FAN PALMS.
The species most commonly used for street and ornamental planting in the
California coast districts is the Chinese or windmill palm.[67] This palm
has a slender trunk clothed with brown fibers, flat fan-shaped leaves,
and rather straight radiating segments. The same species is hardy at New
Orleans and Charleston, and even at Laurens, S. C., at an altitude of 600
feet, but it does not thrive in the sandy soil of Florida.
[67] _Trachycarpus excelsa_ (Thunb.) Wendl.
The vegetable hair palm,[68] a native of Spain, Sicily, and North Africa,
is similar to the Chinese palm but smaller and more compact and with
large, sharp spines on the petioles of the leaves. When young it suckers
from the base, like the date palm, so that clusters of it may be formed.
[68] _Chamaerops humilis_ L.
The Guadeloupe Island palm[69] is one of the most popular species in
southern California in the region of Santa Barbara, Los Angeles, and San
Diego. This palm is a native of Guadeloupe Island, of! the coast of lower
California, and is not known to occur elsewhere in the wild state. It
is well adapted to the cool coast climate of California, but not to the
interior valleys. It is smaller than the Washingtonia palms, with a rather
short trunk, 15 to 20 feet high, and a dense crown of fresh green leaves.
[69] _Erythea edulis_ (H. Wendl.) S. Wats.
The California blue palm,[70] formerly placed in the same genus with
the Guadeloupe Island species, is very distinct in habits as well as
in general appearance, having bluish or grayish green leaves, strongly
toothed petioles, and long, slender inflorescences. The trunk is very
robust, often 2 to 3 feet in diameter, and is said to attain a height
of 30 to 40 feet in Mexico. Several of these features are shared with
the Washingtonia palms. It also has the ability to grow in the dry, hot
interior valleys (regions 3 and 5). In Texas the blue palm has proved
hardy at San Antonio, and even as far north as Austin.
[70] _Glaucothea armata_ (formerly known as _Erythea armata_). See Cook,
O. F., Glaucothea, a new genus of palms from Lower California. _In_ Jour.
Washington Acad. Sci., v. 5, p. 236-241. 1915.
DATE PALM.
The Canary Island date palm[71] is the most popular palm for park or
street planting, being more hardy than the true date palm, larger and more
vigorous in growth, and producing no suckers from the base of the trunk.
Well-grown specimens in the California coast districts (region 2) with
trunks from 2 to 3 feet thick and immense crowns of spreading deep-green
leaves are among the most imposing forms of plant life. Though less robust
in other regions, the species is very hardy and adapted for planting
anywhere in the palm belt (regions 3, 5, 12, and 13).
[71] _Phoenix canariensis_ Hort.
The true date palm[72] is adapted to the warmer parts of regions 3 and 5,
but it is much inferior to the Canary Island species for ornamental use
because the foliage is less attractive, due to its habit of sending out
suckers from the base of the trunk.
[72] _Phoenix dactylifera_ L.
THE COCONUT AND ITS RELATIVES.
The true coconut palm is confined to a narrow belt along the coast of
southern Florida, but other species of cocos are planted in the coast
districts of California. The species that is most prominent in park and
street plantings around San Diego, Los Angeles, and Santa Barbara is
usually known as _Cocos plumosa_ or _Cocos romanzoffiana_, and is a rather
tall, slender palm with a long-jointed trunk about 1 foot in diameter
and long, spreading, feathery, deep-green leaves. Another series is
represented by _Cocos yatay_ and several similar species, often called
_Cocos australis_ in nursery catalogues. They have short, thick trunks,
very glaucous grayish or bluish foliage, and fleshy edible fruits, highly
flavored, somewhat like pineapples. These gray-leaved species are very
hardy. Another coconut relative is the Chilean molasses palm,[73] which
has a massive trunk 3 or 4 feet in diameter, specimens of which are
growing at a few places in California.
[73] _Jubaea chilensis_ Baill.
OTHER PINNATE PALMS.
The amethyst palm, a native of Australia, is commonly planted in
California. It usually appears in lists and nursery catalogues as
_Seaforthia elegans_ or _Archontophoenix alexandrae_, but it is now
recognized as distinct from both of these species and has received a new
name, _Loroma amethystina_. It is the only pinnate-leaved palm, except
certain species of Phoenix and Cocos, that grows freely in the open air
in the coast districts of California, from Santa Barbara to San Diego.
In habit and general appearance Loroma is more like the royal palm,
though with a smaller trunk and fewer leaves. The pinkish purple drooping
inflorescence is very attractive and develops into a large cluster of
scarlet berries.
The royal palms, species of Roystonea, are perhaps the most striking
ornamental members of the whole group. They can be grown in southern
Florida and even exist in the wild state in some of the hammocks below
Miami.
PEPPER TREE.
The California pepper tree[74] is much used in regions 2 and 3 and in the
western part of region 5. It is a moderate-sized broad-headed tree with
fine foliage, which gives it a light, airy appearance. During the fall
and winter it is covered with scarlet berries, which in contrast with the
persistent foliage produce a pleasing effect.
[74] _Schinus molle_ L.
[Illustration: Fig. 28.--A pavement heaved by the roots of poplar trees.]
POPLAR.
Poplars are not desirable for street planting. Their wood is brittle and
easily broken by ordinary windstorms, and their roots run near the surface
and are likely to interfere with pavements, as shown in figure 28, while
those of some varieties are especially liable to make trouble in sewers
by filling them with a mass of fibrous roots if access is once gained.
Vigorous root growth is encouraged by the moisture from a leak, and the
roots ultimately find their way inside.
The southern cottonwood,[75] Carolina poplar, and the northern
cottonwood[76] are so similar in their adaptability for street planting
purposes that they will be discussed together. They are easily propagated,
easily transplanted, are quick-growing, and where they reach maturity
under normal conditions form very large oval-headed handsome trees, but
under the artificial conditions existing in cities it is necessary to
prune them quite severely when young to remove the long vigorous growths
and make the heads more compact. This pruning stimulates more vigorous
growth, which must be removed or they will form long branches with heavy
tops, that are especially liable to be injured by windstorms. The more
they are pruned the greater the tendency to an undesirable form of growth.
They begin dropping their leaves early in the summer and lose them very
early in the autumn. Their root growth is especially vigorous, so that
they are liable to make trouble in sewers in the manner already mentioned.
It is largely on this account that many cities prohibit the planting of
these trees. Except in regions 6, 7, or 8 or in locations where smoke and
fumes in the air prevent the growing of other trees, they should not be
planted.
[75] _Populus deltoides_ Marsh.
[76] _Populus virginiana_ Fouger.
The Lombardy poplar[77] is a tall columnar tree adapted for use on very
narrow streets (fig. 14). It is short lived in many places, due largely to
the European poplar canker, but otherwise is a satisfactory tree for these
conditions in all parts of the United States. The trees may be planted as
close together as 30 feet.
[77] _Populus italica_ (Du Roi) Moench.
None of the other poplars have much to recommend them for street planting.
RUBBER TREE.
The rubber tree[78] is a large-headed handsome evergreen, suitable for
regions 3 and 5 and the southern parts of regions 2 and 13 when the use of
an evergreen tree is warranted.
[78] _Ficus elastica_ Roxb.
SILK OAK.
The silk oak,[79] or Australian fern, is a large, handsome tree that
succeeds well in regions 2, 3, and 13; also in region 5 if provided with a
reasonable amount of moisture, as it stands drought remarkably well. It is
covered in early summer with orange-colored flowers.
[79] _Grevillea robusta_ A. Cunn.
SWEET GUM.
The sweet gum[80] is adapted to regions 11, 12, and 13, especially on
sandy lands. It forms an oval-headed, handsome tree with star-shaped
leaves that assume a particularly brilliant hue in the autumn. It is
better adapted to suburban conditions than to the heart of a city. Toward
the northern limits of its successful cultivation it is difficult to
transplant, while in the warmer sections of the country it can be moved
with comparative ease. It should be transplanted only in the spring.
[80] _Liquidambar styraciflua_ L.
SYCAMORE.
The sycamore[81] also called the buttonwood and buttonball tree, is a
large, open, spreading, quick-growing tree native along water-courses.
It is adapted to regions 1, 2, 3, 4, 9, 10, 11, 12, and 13 and is worth
testing in regions 5, 6, 7, and 8. Its habit of shedding its outer bark
in large flakes, leaving the white new bark showing in large patches,
makes it a conspicuous tree wherever grown. The fruits are balls 1 inch
or more in diameter and are sometimes objected to because they make dirt
when falling; also the shed bark is considered objectionable. It is such
a strong-growing handsome tree and succeeds so well under city conditions
that it is being planted more and more frequently. It will stand more
pruning and shaping than any other street tree. Without pruning it is
too large for ordinary streets unless spaced at almost double the usual
planting distance, with the trees staggered along the street instead
of being planted opposite. Its high head and open habit of growth are
distinct advantages for street planting. Its foliage, too, is a light
green, which gives an impression of airiness with the shade. It is subject
to attack by a fungus that kills the leaves while still small or partially
mutilates them, giving them an unsightly appearance. In some places this
trouble is quite serious.
[81] _Platanus occidentalis_ L.
The California sycamore[82] is a native of California adapted to regions
1, 2, 3, and 4 and portions of region 5. It is similar in general
characteristics to the sycamore.
[82] _Platanus racemosa_ Nutt.
The London plane tree[83] is one of the Old World forms of sycamore.
According to Alfred Render,[84] "the true oriental plane is rare in
cultivation, the tree usually planted under this name being _Platanus
acerifolia_" It it more compact in habit of growth and has the other good
qualities of the sycamore. It is being more and more used on city streets
and is proving satisfactory in regions 1, 2, 3, 4, 9, 10, 11, and 12. It
will probably succeed in the warmer parts of regions 6 and 7 and also in
regions 5 and 8. It is a more desirable tree for ordinary use than the
sycamore, on account of its more compact habit and comparative freedom
from disease, though it is tender in the northernmost sections.
[83] _Platanus acerifolia_ (Ait.) Willd.
[84] Bailey, L. H., ed. New York, 1916. Standard Cyclopedia of
Horticulture, v. 5, p. 2707.
TULIP TREE.
The tulip tree[85] is also sometimes called the tulip poplar or yellow
poplar, though the latter names are unfortunate, as the tree is not
a poplar or even closely related to the poplars. It is a large,
rapid-growing tree suitable for suburban conditions in regions 1, 2, 10,
11, and 12. The leaves are of unusual form, the upper half appearing to
have been cut away, leaving a notch about where it would seem the middle
of the leaf should be. The color is a light green. The roots are unusually
soft and tender, and therefore the tree needs to be transplanted quickly
and with great care. Small sizes should be planted, especially near the
northern limits of growth. It should be transplanted only in the spring.
If after transplanting it the top should die and a new vigorous shoot
should put out from the root, it would be desirable to form a new top from
this shoot rather than to transplant another tree.
[85] _Liriodendron tulipifera_ L.
CULTURE OF STREET TREES.
SELECTION OF INDIVIDUAL TREES.
Nursery-grown trees should be used for street planting, and they should
have been transplanted at least every two years while in the nursery.
This is to insure a thorough root pruning and the production of numerous
fibrous roots close to the trunk. Trees not frequently transplanted form
a few long roots that are largely cut off when the tree is dug. Trees
growing in the woods form a few very long roots, and when an attempt is
made to dig them only a little of the root next the trunk is obtained,
while most of the roots, including the fibrous ones, are left in the
ground. If woodland trees are wanted for street purposes, most kinds
should be grown for a few years in a nursery in order to form a good root
system before being planted on the streets.
In addition to a good root system, the tree should have a straight
trunk for the variety, with a good set of branches, called the head,
the bottom branches being from 7 to 9 feet from the ground. Trees which
naturally head low should be started with a higher head than those
varieties that have a tendency to an upright growth. A good head for a
shade tree is a leader or upright branch with three or more side branches
about equally spaced around the tree. The trees should be healthy, free
from scars, and also free from evidences of insects or diseases. In the
presence of insects, trees should be thoroughly fumigated along approved
methods before leaving nurseries, to insure against the introduction and
distribution of pests. Weakened vitality resulting from transplanting and
subsequent neglect will frequently invite attack by bark-boring insects
which seriously damage or kill the trees. Mulching and watering will often
prevent this damage.
Opinion as to the size to plant differs somewhat, but for average
conditions trees from 10 to 12 feet high and with trunks or stems from 2
to 2-1/2 inches in diameter[86] are very satisfactory in most varieties
used for street purposes. With such varieties as elms sycamores, and some
southern oaks, somewhat larger trees can be used equally well, while
smaller trees would be better in the regions of limited rainfall both
east and west of the Rocky Mountains and for tulip trees and sweet gums,
especially in the northern portion of their range of usefulness.
[86] Designated by nurserymen as "caliper."
PREPARATION OF HOLES.
Next to the selection of a proper variety, the preparation of the hole
is the most important detail of street tree planting. Because of the
restricted area available for the spread of the tree roots, and owing to
the artificial conditions imposed by the improvement of city streets, the
soil provided for the feeding ground of the roots of the young tree must
be liberal in quantity and of the best quality. From 2 to 3 cubic yards of
soil should be provided for each tree. It is desirable to have at least 18
square feet of opening in the sidewalk, especially if it is of concrete or
other impervious material. Trees will grow with smaller sidewalk openings,
but they are not likely to thrive so well, and it is impossible properly
to prepare a hole for planting a tree without disturbing at least this
much surface soil. The proper depth of soil is from 2-1/2 to 3 feet. A
hole 3 feet deep large enough to hold 2 cubic yards of soil has a surface
area of 18 square feet. A hole 6 feet long, 3 feet wide, and 3 feet deep
will hold 2 cubic yards of soil, will have the smallest desirable surface
area, and will be of such dimensions as will best conform to the usual
sidewalk and roadway widths and thus not interfere with traffic.
The tree hole must be so drained that water will not stand in it. If the
soil is so impervious as to hold water some artificial drainage must be
provided. That portion of the depth of a hole that acts as a cistern for
holding water is valueless as a feeding ground for roots. For every cubic
foot of soil in the bottom of a hole that might thus be made valueless by
standing water, 1-1/2 cubic feet of soil should be added by increasing the
length or width of it. Under no circumstances, however, should the depth
of available feeding ground be less than 2 feet. The deeper the roots may
be encouraged to grow, the less injury is likely to be experienced from
drought.
The soil used should be topsoil from land that has been producing good
crops. This should be well enriched with rotted manure, one part of manure
to four of soil. The addition of such fertilizers as ground bone, tankage,
fish scrap, or cottonseed meal at the rate of 1 pound to the cubic yard of
soil is also helpful. Commercial fertilizers containing mostly phosphoric
acid obtained from other substances than ground bone are not to be
recommended for use in the soil about the roots at planting time. When
used they should form a surface application, worked into the soil after
planting.
PLANTING.
If trees are shipped from a distance they should be taken at once on
arrival to some point where the roots may be carefully covered with soil;
there they should be unpacked and plenty of loose moist earth worked
thoroughly around and over the roots as fast as they are taken from
the box. This temporary covering of the roots is called "heeling in."
(Fig. 29.) The tops may be either erect or laid almost on the ground in
successive rows, the tops of one row lying over the roots of the previous
rows, the object being to cover the roots thoroughly and keep them moist
until the tree is wanted for permanent setting. Not a moment of exposure
should be permitted between the box and the soil. If the roots appear dry,
they may be dipped for a few minutes before "heeling in" in a tub of water
or in thin mud.
[Illustration: P20370HP
Fig. 29.--Trees properly "heeled in."]
[Illustration: P20000HP
Fig. 30.--Trees handled in a careless manner. The roots should have been
covered with wet canvas.]
Trees in large quantities are often packed directly in cars with a small
quantity of straw about the roots. When shipped in this way extra care
(compare figs. 30 and 31) must be exercised in taking the trees to the
point where they are to be heeled in. The wagon in which they are to be
hauled should have a tight box, and wet canvas should be tied tightly over
the load. The last is important, so that there may be no chance for the
roots to dry.
When taking trees from the ground where they have been heeled in to the
place for planting, great care must also be exercised to see that the
roots are not exposed to sun or wind, but are kept closely covered with
moss, wet burlap, or canvas until planted. Lack of care in this matter
is a greater cause of loss in tree planting than carelessness in any
other particular. One city that has its own nursery and uses largely
trees that are supposed to be difficult to move, but is careful about not
exposing the roots for a moment (fig. 31), has a loss of less than 1 per
cent. If the roots once dry the trees will die, and it takes but a short
exposure to dry the roots. The holes should be prepared well in advance
of planting, so that no time will be lost when conditions are right for
putting the trees in the ground.
[Illustration: P20350HP
Fig. 31.--A load of trees and tree boxes. The roots are packed in wet moss
and a tree is not taken from the wagon until the planter and two shovelers
are at the hole where it is to be planted.]
In regions 1, 10, 11, 12, and 13 (fig. 17) the best time for planting
deciduous street trees is the month or six weeks just preceding freezing
weather in the fall. The other desirable time for planting is as soon
after freezing weather is over in the spring as the ground is dry enough
for the mechanical operations. This should be as early as possible, as the
more opportunity there is for root growth before warm weather forces the
top into growth, the better the results are likely to be. In regions 6, 8,
and 9, where the ground freezes to a considerable depth, spring planting
is to be preferred to fall planting unless it is possible to drench the
soil thoroughly for a considerable distance around the trees at planting
time and after that to mulch the soil thoroughly and also to protect the
top from the effect of drying winter winds. Where mice abound they may be
harbored in the mulch and may girdle the tree. This may be prevented by
a collar of wire netting about the base of the trunk or by banking the
earth about it. The death of trees at the time of transplanting is due to
the drying out of either roots or tops before opportunity is given them
to become reestablished in their new locations. This drying may be due to
improper exposure at the time of digging or before packing (fig. 30), poor
packing, prolonged delay in delivery, improper handling between unpacking
and planting, or the existence of conditions conducive to excessive drying
out of the plant after setting.
[Illustration: P14340HP
Fig. 32.--A city nursery.]