Trees for shade should be planted only after thoughtful selection, for those that may be very suitable in June may be less so in August. The Linden and the Mulberry are delightful trees when they come into leaf, but in July and August the former may make everything near by dirty with dripping honeydew, and in August and September falling Mulberries stain almost everything with which they come in contact.
Moreover, on a hot day in summer, people may not question the kind of tree that gives them shade, but when shade is unnecessary they become critical if some common and uninteresting subject is standing in a conspicuous position on a lawn.
Trees growing on lawns are not the only ones that have to be considered; the whole subject of trees for the sides of roads and streets must be taken into account, also field trees where shade and shelter are necessary for stock. Further, the trees that may be desirable for some locations and for some regions are undesirable for others.
Shade trees are also necessary for the successful cultivation of some kinds of plants. Many of the Rhododendrons, particularly those with large leaves, succeed better under the partial shade of Oak or Pine trees than when exposed to full sun. Ferns can also be more easily grown in moist ground beneath trees than in full sun, as well as certain kinds of Primulas, Liliums and other plants.
Selecting Shade Trees
Shade Trees for Planting on Lawns. When a garden is not large enough to allow of the inclusion of a number of trees, the selection of one or two is of great importance. When making a choice, the planter should try to visualize the frees at maturity. A particular tree may be extellent when half-grown, but be quite out of place when full size.
Thus trees of the largest size should not be planted in places where, at maturity, they are likely to endanger the safety of a house or other building, or to exclude light and air from rooms. Trees of the largest size should not be closer to buildings than their own average height at maturity. It is not wise to plant trees in places where they are likely to cause damage by falling branches when they have grown to a large size.
The Best Kind of Tree to Choose. A shade tree on a lawn should have many virtues. It should be a safe tree, or as safe a tree as it is possible to choose; that is to say, one that is not likely to shed heavy branches either on a calm day or during a storm. It should not be a kind that is likely to be struck by lightning, and should be capable of producing a distinct length of clean trunk 8-10 ft. high. The branches should be fairly wide spreading and droop to within a few feet or so of the ground, or, in the case of weeping trees, be just clear of the ground.
The great value of shade trees is that full advantage may be taken of the shady leaf surface without the inconvenience of low inside branches. Careful pruning during the early life of the tree will do much to assure the development of a tree of this type.
The shade the tree gives should not be so dense as to kill the grass beneath the branches. Conspicuously placed trees should be of good appearance from the time they come into leaf until autumn, or, in the case of evergreens, throughout the year; they must be hardy enough to withstand the greatest cold experienced in the place where they are planted. Moreover, they should not be unduly subject to insect attacks or to serious diseases.
The fastest-growing trees are not the best shade trees and only under very special circumstances should they be considered at all. Generally they have soft, brittle wood and weak crotches and are excessively liable to damage by storms; often they are extremely susceptible to diseases and pests. Some, notably Poplars and Willows, have far-reaching roots that are very likely to enter drains even at considerable distances from the tree, stop them up and cause serious damage. They may even harm foundation walls if these are not well constructed.
Among fast-growing trees to be generally avoided as shade trees are Box Elder, Catalpa, Poplars, Siberian Elm, Silver Maple, Tree of Heaven (Ailanthus) and Willows. Under very special circumstances some of these may be used, but not if better trees can be expected to grow in the chosen location.
There are some situations where these fast-growing shade trees might be chosen. For example, in city gardens where growing conditions are extremely difficult, a Tree of Heaven is most likely to survive and thrive. In certain parts of the West where the choice of trees that will grow is extremely limited, a Box Elder may well be the best selection.
While very fast-growing trees are usually undesirable, there are many trees that make a good medium growth each year and are excellent for shade purposes, and there are a number of slower growth that are worth considering.
Not Good Risks. Several kinds of trees that have been used extensively in the past as shade trees are no longer considered good risks because of their susceptibility to diseases or pests which in recent years have become prevalent and for which, at present, there is no satisfactory control or none that is relatively easy to apply at a reasonable cost.
The American Elm is perhaps the best-known tree in this group. The spread of the devastating Dutch Elm disease and the great damage done to the Elm by the Elm Leaf Beetle are so serious that, fine tree though the American Elm is, it can no longer be recommended for general planting.
Certain Oaks are seriously affected by a Wilt disease that makes their planting hazardous in localities where this disease exists, or near places where this disease occurs. Before planting a new shade tree it is always wise to inquire of your State Agricultural Experiment Station whether there is any disease or pest prevalent in your section, or likely soon to spread to your locality, that may be extremely serious.
When selecting kinds of shade trees, consideration must be given to soil as well as to location. Acid-soil trees such as most Oaks will not thrive on alkaline soils, such as are found in many parts of the West, even though climatic factors may be favorable. Trees that grow naturally on moist soils usually will not grow well on dry soils, and trees that need porous, sandy or gravelly soils may resent a heavy clay soil.
Before deciding on the kind of shade tree to plant, it is wise to tour the neighborhood to determine which kinds are already thriving. It is wise, too, to consult a reliable nurseryman or informed gardener who knows trees and understands local conditions. Your State Agricultural Experiment Station will also be glad to help you in making your choice.
Nursery-grown trees are much easier to transplant than trees taken from the wild. This is because such trees have been transplanted frequently, which treatment results in the development of a compact mass of fibrous roots rather than the longer, more rambling roots of trees that have grown in one place without disturbance.
The size of tree to plant depends upon how quickly you require shade and what price you are prepared to pay. With the aid of modern equipment and techniques it is possible for experts to transplant successfully trees of huge size, 60 ft. tall and higher, but the cost is great and the operation is not a practical one for most home gardeners to have done.
Trees 20-25 ft. tall and of nearly the same spread can be moved by capable nurserymen without special equipment beyond that ordinarily available in a nursery, and such trees will usually be the largest that the average gardener will have planted. The cost of such a tree and its planting in the selected location will amount to a fairly substantial sum, but when one considers what the money buys, the years and care the tree has taken to develop, and the waiting that will be necessary if a smaller specimen is planted, it may be very worth while. There is no doubt that well-selected and well-located shade trees add substantially to the actual cash value of a house.
Smaller and younger trees are more frequently planted. Specimens 10-12 ft. tall are comparatively inexpensive, are easily handled and in 10-20 years develop into sizable specimens. They give little or no shade at first.
Choosing the particular tree follows the decision of the kind of tree to plant. It is wise to visit the nursery personally for this purpose.
The tree selected should be symmetrical and straight. It is important that its leader (central shoot) be undamaged and intact. A divided trunk or bad crotches between limbs that may tear apart later when the branches become heavier are bad faults.
It is important that the tree be vigorous and that it should have been making a reasonable amount of growth in recent years. Needless to say, it should not have any serious infection or be damaged by borers or other serious insect pests. The bark should be intact, not damaged by frost cracks (these longitudinal splits occur on the south side of the tree as it has been growing) or by accident. Any old pruning cuts present should have healed over or should be in the process of healing rapidly.
The time to plant shade trees varies somewhat according to local conditions but in nearly all situations the most favorable times for leaf-losing kinds are just before new growth begins in spring, and in early autumn about the time the leaves are falling. Evergreen kinds are best transplanted just before new growth begins in spring or in late summer or early fall.
Whatever the kind of tree and its size at planting time, it is of the utmost importance to set it in a hole much larger than the spread of the roots, to have the hole prepared by digging over its bottom and incorporating generous amounts of compost, rotted manure or other humus-forming material, and to fill good, rich soil around and between the roots. Good planting in good soil goes far toward ensuring the well-being of the tree.
The tree should be set at the same depth as it has previously been, or at the most an inch or two deeper. Deep planting is very harmful.
After the tree has been set in place and the hole filled to about three-quarters of its depth with good soil, and this has been rammed firmly, the remainder of the hole should be filled with water once or twice. This should be allowed to soak in before the soil fill is completed.
The surface is finished by making a slight depression over the area the tree roots occupy and encircling the area with a slight ridge or mound of soil. This makes it possible to water the newly planted tree more thoroughly during the first season after it is planted.
Trees may be planted bare-rooted (without soil attached to the roots) or with their roots contained in a mass of soil which is called the “ball” and which is usually tightly wrapped in burlap. Trees handled in the latter manner are said to be balled and burlapped.
When planting bare-rooted trees, it is very important to spread the roots out in the way they grew naturally and to work good soil between them and pack it firmly. It is harmful to crowd the roots and bunch them together.
When planting balled and burlapped trees, great care must be taken not to break the ball; as much of the burlap as can be removed without damaging the ball is cut away after the tree is in position in the hole and before any soil is filled in. Evergreen trees are always planted with a ball, never bare-rooted.
After planting, bare-rooted trees, and sometimes balled and burlapped specimens, are secured against disturbance by wind by guying them with three stout wires attached to pegs driven into the ground well beyond the spread of the hole. Where the wires pass around the trunk or branches of the tree they are threaded through short pieces of rubber hose to prevent damage to the bark.
It is a good plan to wind a spiral of burlap, or of special paper made for the purpose, around the trunks of newly planted trees that have thin, smooth bark. This is left in position for about a year. It prevents the bark from splitting under the influence of the sun, which it is apt to do before the tree regains its vigor after the shock of moving, and also tends to prevent the entry of borers.
A mulch (surface covering) of two or three inches of coarse compost, littery manure, half-decomposed leaves, peat moss or some similar material placed over the soil occupied by the roots after the tree is planted is beneficial. During the first summer following planting, great care should be taken to soak the roots with water thoroughly at weekly or ten-day intervals during periods of drought. Enough water should be given at each application to soak in to a depth of at least a foot.
Pruning trees at planting time needs considered attention. Because the roots have been reduced in the process of transplanting, it is usually desirable to reduce the size of the top somewhat. This pruning should consist of the thinning out of weak and ill-placed branches and the shortening of some others. The leader (central shoot) should not be shortened. All pruning cuts exceeding 1 in. in diameter should be painted with special tree-wound paint or with ordinary white lead paint into which a liberal amount of powdered sulphur (a fungicide) has been stirred. Before the wounds are painted they should be sealed with a coat of shellac dissolved in alcohol.
Maintenance of Shade Trees
Pests and Diseases. Like all garden plants, shade trees need intelligent attention in order to thrive. Every effort should be made to keep them free of diseases and pests. This means that the trees should be carefully inspected from time to time and that at the first evidence of trouble prompt control or preventive measures should be taken. It is well for the gardener to familiarize himself with the pests and diseases that are most likely to be bothersome to specific trees and to watch for these. (See Pests and Diseases.) Much useful information is available in bulletins on the pests and diseases of shade trees that have been published by State Agricultural Experiment Stations.
Pruning may need periodic attention. IllIII-placed, broken and disease-damaged branches should be removed promptly. Sharp tools only should be used and clean cuts should be made. Branches should be shortened to a good side branch or be cut off flush with the trunk. Stubs that rot and encourage decay to spread into healthy parts of the tree should never be left. After each cut is made, it should be painted with shellac dissolved in alcohol in a ring extending for half an inch or so within the bark (this will protect the cambium layer) and then the whole cut surface should be given a coat of tree-wound paint.
Fertilizing is an important routine in keeping shade trees healthy, particularly those growing in poor soils and those that have reached maturity and are growing less vigorously than they were earlier in their lives. Special complete fertilizers or tree foods are available, and these form a simple and effective way of supplying trees with needed nutrients.An alternative method is to spread a layer of partly rotted animal manure and a dressing of superphosphate over the area occupied by the roots. Such a mulch is of great benefit. Even if fertilizer is relied upon to provide needed nutrients, a mulch of compost, leaf mold or peat moss is highly beneficial because it keeps the roots cool and more evenly moist than would otherwise be the case. When trees are located in lawn or sod such mulches are obviously impracticable; then fertilizers alone must be relied upon.
The fertilizer may be spread over the soil surface, but it is a better plan to bore holes with a crowbar or special power tool in a pattern extending over the outer three-quarters of the area in which the roots spread. This area normally extends slightly beyond the spread of the branches and two or three times as far in the case of narrow, more or less columnar trees.
The holes should be about 2 ft. deep and may be spaced 2 ft. apart. They should be about 2 in. in diameter. The holes are filled to within 4 in. of their tops with special tree food. Soil and, if needed, plugs of grass sod are used to complete the filling of the holes.
Manufacturers’ directions should be followed in determining the amount of tree food to apply at one time. Normally three pounds of specially prepared food are applied for every inch the trunk measures in diameter at about 4 ft. from the ground.
Fertilizing may be done in spring or late summer. Ordinarily an application made every second year is sufficient.
In times of drought, watering shade trees periodically is of great benefit. An application made every ten days will do an immense amount of good. Whenever water is given, enough should be used to soak in to a depth of at least 1 ft.
Tree surgery, including the treatment of open cavities, cavity filling, bracing and cabling and sometimes the installation of lightning rods is specialized work that is normally done by expert tree surgeons. Wisely used, tree surgery can do much to prolong the useful lives of shade trees, but unskilled work is of little help and it sometimes happens that amateur gardeners are encouraged by commercial concerns to have more tree surgery done than the site and situation warrant.
Even if professional services are not employed, it is always wise to clean cavities of all rotting tissue, to shape them so that the edges are smooth and water will not collect in them (it may be necessary to bore a hole and insert a piece of iron or galvanized pipe sloping downwards from the bottom of the hole to the outside of the trunk to ensure this) and to paint the exposed surfaces once a year with special tree-wound paint. See Tree Surgery.
Selecting Shade Trees
The kinds of shade trees that are to be recommended for planting in Canada and the United States vary according to region. In the North, evergreen trees are not usually planted as shade trees although they are used extensively for landscape effects and do, of course, serve to provide shade. In the South, where bright hot sunshine is more prevalent, it is very usual to plant evergreens for shade. The size of the lot and the style of the house will often have a bearing on the suitability of a certain tree as a shade tree. Traditionally we think of shade trees as including only kinds that grow to large or fairly large size, but with the rapid increase in the number of smaller and lower houses being built on small or medium-size lots many smaller trees may with advantage be considered.
Recommended Shade Trees
Ash, Green (Fraxinus pennsylvanica variety lanceolata). A fairly narrow tree of quite rapid growth. Hardy to northern Canada. Prefers deep, rich soil but stands dryness remarkably well. A good tree for the Plains and Prairie regions of the Middle West and useful elsewhere in the North.
Ash, Velvet (Fraxinus velutina). A round-headed tree of rather open growth that attains a height of 45-50 ft. It is fast-growing, drought-resistant and stands alkali soils quite well. It is adapted only for mild climates and is recommended for the drier parts of the Southwest. It thrives best in a reasonably fertile soil.
Beech, European (Fagus sylvatica and its varieties). Eventually very large, with a dense, broad head and smooth, light gray bark. Roots near the surface and does not thrive in compacted (packed down) soil. Under old specimens it is not usually possible to grow grass or other plants. There are several fine varieties of this noble tree including cut-leaved or fern-leaved kinds and kinds with purple foliage. The variety called tricolor has variegated leaves and is very handsome. It does not grow so large as the other kinds.
Box Elder (Acer Negundo). For use only where more desirable trees will not grow. Best on moist soil but stands drought well. Plant male trees only; females are hosts of the Box Elder Bug.
Camphor Tree (Cinnamomum Camphora). Evergreen. Well-established trees resist temperatures as low as 15 degrees. Dropping of abundant fruit may be something of a nuisance.
California Pepper Tree (Schinus Molle). A broad-topped evergreen of very attractive appearance. It bears clusters of very beautiful rose-pink berries that follow small, yellowish-white flowers. This tree is drought-resistant and fairly tolerant of alkali soils. It gives light shade. Best suited for California. A related kind, S. terebinthifolia (the Brazilian Pepper Tree), has bright red fruits and is suitable for planting in Florida. Both attain a height of about 20 ft.
Cape Chestnut (Calodendrum capense). An evergreen tree, round-headed, that attains a height of up to 70 ft. It bears attractive, rose-lavender flowers and has handsome, dark green foliage. It is suitable only for very mild climates such as those of southern Florida and southern California.
Cork Tree (Phellodendron amurense). Gives light shade. A low-branched tree with a broad, spreading top. Resistant to pests and diseases and has handsome foliage and attractive bark. Is tolerant of city smoke. Hardy as far north as Newfoundland, southern Ontario and British Columbia. A related kind, P. sachalinense, is similar and equally as satisfactory. These trees attain maximum heights of about 50 ft.
Ginkgo (Ginkgo biloba). A tree of somewhat erratic branching habit that casts light shade and is notoriously free of disease and insect pests. A good tree for city planting. Male and female flowers are borne on separate trees. The fruits, which are borne by female trees only, of course, have a very objectionable odor; for this reason male trees only should be planted when it is possible to obtain specimens identified as to sex. At maturity Ginkgos attain a height of 100 ft. or more.
Golden-Rain Tree (Koelreuteria paniculata). Widespreading, round-topped, 20-30 ft. tall. Graceful foliage. Large clusters of yellow flowers in summer, followed by attractive fruits in fall. Fairly rapid grower. Stands heat and drought and tolerates alkali soil better than any other tree.
Hackberry (Celtic occidentalis). A wide-spreading tree, 50-70 ft. tall, that gives moderate shade. It has somewhat the appearance of an elm but is less graceful. It is not tolerant of smoke and soot. It is hardy into northern Canada. A less hardy kind, but one that is to be preferred where it can be grown (as far north as southern New England), is C. laevigata. This Hack-berry is resistant to the witches’-broom disease that disfigures C. occidentalis.
Honey Locust (Gleditsia triacanthos and varieties). This fine tree gives light shade, and grass grows well beneath it. It is a fairly fast grower and stands city conditions well. The seed pods are something of a nuisance when they fall, but a modern, thornless form of this tree, known as the Moraine Locust, does not produce pods. This is recommended as a substitute tree for the American Elm.
Kentucky Coffee Tree (Gymnocladus dioica). Gives light shade. Prefers moist soil but adapts itself to drier locations. Subject to cotton root rot disease. Do not plant on infected soils.
Linden, Silver (Tilia tomentosa). Eventually large, with dense, broad head. Small, fragrant, creamy flowers in summer. Tolerates heat and drought. Good near the seacoast. Not good in smoky areas. Said to be poisonous to bees when in bloom.
London Plane (Platanus acerifolia). Eventually large and spreading. Stands pruning well. Good in cities. Alkali-tolerant. Subject to some diseases and pests but less so than the native American Plane (Sycamore).
Madrona (Arbutus Menziesii). Evergreen. Grows moderately rapidly. Does not stand cold or wind well. Needs sheltered location.
Maple, Norway (Ater platanoides). Gives heavy shade from a rounded head. Tolerates a wide variety of soils. Good city tree. Has surface roots and so it is difficult to grow grass beneath it. The Schwedler variety has leaves that are deep bronze in spring. The variety Crimson King has deep purplish-red foliage Not hardy in all parts of Rocky Mountain region.
Maple, Sugar (Acer saccharum). Large at maturity. Not suited for polluted atmospheres. Best in moist, rich soil. Gives wonderful fall color. Subject to wilt disease and, in hot, dry weather, to scorching of its foliage.
Oak, Bur (Quercus macrocarpa). Large, slow-growing. Has massive head. Gives moderate shade. Drought-resistant and hardy. Do not plant on soil infected with cotton root rot fungus.
Oak, Coast Live (Quercus agrifolia). Evergreen. At maturity, broad-spreading. Grows slowly at first, faster later. Do not plant in lawns or other constantly irrigated areas.
Oak, Live (Quercus virginiana). Evergreen. Rather slow-growing. Huge at maturity. Broad-topped. Needs plenty of room. Is damaged by severe frosts. Resists insects and diseases.
Oak, Northern Red (Quercus borealis). Eventually large. Has a short trunk and spreading branches. Good fall color. Thrives in gravelly and sandy soils, not in wet ones. Subject to Oak wilt disease where this is prevalent.
Oak, Pin (Quercus palustris). Straight-trunked, with many slender branches and of fine appearance. Good autumn color. Tolerant of a wide variety of soils (except alkaline ones) and of city smoke.
Oak, Scarlet (Quercus coccinea). A fine tree. Prefers dry sandy soil. Endures city conditions well. Foliage colors handsomely in fall.
Oak, Water (Quercus nigra). Eventually large, symmetrical. Grows rapidly in early life. Leaves stay on late in the fall. Tolerant of wide variety of conditions.
Oak, White (Quercus alba). Sturdy, with broad, rounded, open top. Eventually large. Leaves turn brown in fall and hang on late. Subject to wilt disease where this occurs.
Oak, Willow (Quercus Phellos). Handsome, graceful, large tree. Leaves willow-like, light green. Grows quickest in moderately moist soils but stands dry soils also.
Pagoda Tree, Chinese Pagoda Tree, Chinese Scholar Tree (Sophora japonica). Has broad, rounded, spreading top. Casts light shade. Has attractive yellow-white flowers in summer. Young trees more susceptible to winter cold than older, well-established specimens.
Russian Olive (Elaeagnus angustifolia). A small tree. Survives on sandy and alkaline soils but prefers rich, moist soil. Drought-resistant.
Southern Magnolia (Magnolia grandiflora). Large, handsome, symmetrical, evergreen. Beautiful cream-white fragrant flowers. Rather slow-growing. Stands a variety of conditions but not poor soil drainage.
Sweet Gum (Liquidambar Styraciflua). Has a narrow or fairly broad, open top. Trunk straight. Its foliage colors brilliantly, crimson and wine-purple, in fall. For moist, nonalkaline, well-drained soils. A little difficult to transplant. Plant in spring.
Tulip Tree (Liriodendron Tulipifera). Tall, straight-trunked, with an open top. Its foliage colors bright yellow in fall. Large, greenish-yellow flowers in spring. For fairly moist, loamy soils. Not easy to transplant. Move young specimens only, in spring. Leaves drop over a long period.
Tupelo or Sour Gum (Nyssa sylvatica). Casts moderate shade. Has an irregularly shaped top. Needs rich, moist soil. Brilliant scarlet foliage in fall. Difficult to transplant. Set out small trees only, in spring.
Yellow Wood (Cladrastis lutea). Medium-sized, broad-topped. Foliage colors bright yellow in fall. Fragrant white flowers in June. Prefers rich, moist soil but is drought-resistant. A fine shade tree. Plant in spring. Transplanted specimens re-establish themselves rather slowly.