Closely related to the hornbeams and birches is this small, waterloving tree that grows very rapidly and serves definite, special uses. The genus Alnus includes 20 species, nine of which grow in North America and six of which reach the height of trees. Alders may be planted in hedges along the borders of streams where their closely interlacing roots hold the banks from crumbling and keep the current clear in midstream. Like willows, alders are of assistance in draining wet soils.
In America the black alder (Ilex verticillata) is often found in horticultural varieties. The daintiest are the cut-leaved forms, of which imperialis, with leaves fingered like a white oak, is a good example. The root nodules add nitrogen to the soil, the black alder being the only nonleguminous plant that is able to perform this function. (See Legumes in the Soil Improvement chapter.)
Azaleas, holly, pieris, and rhododendrons are good companions for a landscape planting because all like humusy, acid soil. Do not plant azaleas or rhododendrons near black walnut trees. The substance called juglone washed from the leaves of black walnuts is detrimental to them.
Beech trees and ferns often grow together, and scilla bulbs do well under the trees. Beech trees in their infancy do well under the shade of other trees, so each fruiting tree is the mother of many young ones.
It is believed that birch roots excrete substances that encourage fermentation and make the trees useful to plant around manure and compost piles. Dr. Ehrenfried Pfeiffer, one of the early advocates of the biodynamic method of farming and gardening, observed that composts fermented in the vicinity of the gray birch derived benefit from it and suffered no losses of nutrients even if the roots actually penetrated the heap. It is considered best, though, to maintain a distance of at least six feet from the tree when building a compost pile.
Turpentine substances washing from the leaves of conifers such as pine trees will inhibit the fermentation process of compost piles. Interplanting onions with conifers will help prevent damage by squirrels, which eat the buds of Scotch, white, and red pines. Winter-hardy Egyptian onions are the best kind.
Squirrel damage in pines and other trees can be limited by planting onions nearby.
Pine needles make an attractive mulch and will increase the stem strength, flavor, and productiveness of strawberries. In general, conifers have an adverse effect on the growth of wheat, since rain washing over them picks up substances that inhibit the germination of seeds.
Elderberries, having a liking for moist soil, are helpful near compost yards that are difficult to drain, and will also assist in the fermentation of the compost. Elderberries are noted for their ability to produce very fine humus soil about their roots.
Grapevines that climb trees, swinging high in the air, are greatly benefited by good air circulation and sunlight. It is the sunlight on their leaves rather than on the grapes that causes them to ripen to perfection. Elm trees are particularly beneficial as supports for grapevines.
The slippery elm (U. fulva) is also known as the red elm because its wood is red and the moose elm because moose are fond of browsing its young shoots. When the bark is stripped from this valuable tree, it is possible to scrape from its inner surface the thick, fragrant, mucilaginous cambium — a delectable substance that allays both hunger and thirst. The inner bark, dried, ground, and mixed with milk, is a valuable food for invalids. Fevers and acute inflammatory disorders have been treated with the bark, and poultices of the bark also relieve throat and chest ailments.
Hedges used as windbreaks are of particular value in dry, windy areas. Blueberries make a delightful hedge where they can be grown. Rosa rugosa makes an almost impenetrable hedge and also affords a harvest of vitamin-rich rose hips. ‘Cardinal’ autumn olive (Elaeagnus umbellata ‘Cardinal’) and dwarf burning bush (Euonymus alatus com pactus) are beloved by birds, as is red-leaf barberry (Berberis thunbergii atropurpurea). For brilliant color there are ‘Golden Prince’ euonymus (Euonymus fortunei) and ‘Gold-flame’ spiraea (Spiraea bumalda).
Sweet pea–type blossoms on a tree, or pods like the pea’s swinging from the twigs, mean that it’s a member of the pod-bearing Leguminosae family, to which both herbaceous and woody plants belong.
The black locusts (R. pseudacacia) have nectar-laden, white flowers of “butterfly form,” which honeybees (leading a host of other insects) swarm about as long as a flower remains to offer its sweet nectar. Cross-fertilization is the advantage the tree gains from all it gives.
Locust, good to plant as a border, has leaves, roots, and bark that are poisonous if eaten, but the pods of honey locust (Gleditsia triacanthos) contain a sweetish pulp used as cattle feed and occa-sionally eaten by small boys, who brave the tree’s thorns to get them.
Being a leguminous tree, the black locust is a good companion to lima beans. There are toxins dangerous to humans in the leaves, bark, and roots, however.
The single genus Acer includes from 60 to 70 species widely distributed over North America. Acer saccharum, the sugar maple, is the best known and economically the most important for both its beautiful wood and its sap, which yields maple syrup. The black maple (A. nigrum) is the sugar maple of South Dakota and Iowa. Red maple (A. rubrum), perhaps the most beautiful of all, is a swamp lover but will thrive on hillsides if the soil is moist. It is widely planted in parks and along streets.
Maples have shallow, spreading root systems and it is difficult to get other plants to grow near them. They may also excrete substances that inhibit the growth of some plants, particularly wheat. Maple leaves laid in layers between apples, carrots, potatoes, and other root vegetables have a preservative effect.
White mulberry is the chosen food of silkworms and no substitute has ever topped this tree’s preeminence. The berries of the red mulberry (M. rubra) do not compare with the cultivated type, but are of value in poultry yards and hog pastures, where they are eagerly devoured. The black mulberry (M. nigra), believed a native of Persia, has large, dark red, juicy fruits but is hardy only in the southern and Pacific Coast states, where it is a desirable tree because it is so attractive to birds.
Mulberry trees are particularly good as a support for grapes. Tree-grown grapes are more difficult to pick than trellised grapes, but they will be relatively free of fungus diseases due to better circulation of air around them. Worms in horses may be repelled by mulberry leaves, and Russian mulberry is sometimes used as a trap crop to protect cherries and strawberries.
As abandoned fields again become covered with vegetation, the brushland is gradually reforested. The first trees are quick-growing, short-lived types that provide conditions suitable for the slower-growing, longer-lived trees. Looking at the forest floor, you will see very few pine seedlings. Other seedlings — young oaks, black cherries, and hickories — do better. Gradually the pines will die off and the young hardwoods grow up and take their place. Should a forest fire occur, the whole process will start over again.
Pod-bearing (leguminous) trees have the power to take nitrogen out of the air and store it in their roots and stems. The decay of these parts restores to the soil the plant food that is most often lacking and most expensive to replace. These trees and shrubs include black locust (Robinia pseudacacia); bristly locust (Robinia hispida), sometimes called rose-acacia; clammy locust (Tobinia viscosa); Scotch broom (Robinia scopariua); honey locust (Gleditsia triacanthos); Kentucky coffee tree (Gymnocladus dioicus); redbud (Cercis canadensis), sometimes called Judas tree; yellowwood (Cladrastis lutea); woad waxes (Genista tinctoria), sometimes called dyer’s greenweed; indigo bush (Amorpha fruticosa), sometimes called false indigo; mesquite (Prosopis juliflora), screwbean (Prosopis pubescens), a slender-trunked mesquite, sometimes called screwpod; Palo Verde acacia (Cercidium torreyanum); Jamaica dogwood (Icthyomethia piscipula); horse bean (Parkinsonia aculeata); Texas ebony (Zigia flexicaulis); and frijolito (Sophora secundiflora).
Black alder (Ilex verticillata) also adds nitrogen to the soil. It is the only known nonleguminous shrub with root nodules that can do this. (See Alder in this chapter.)
Oaks grown with American chestnuts seem to give them some resistance to chestnut blight. During their growth, oaks accumulate a large amount of calcium in their bark, yet amazingly the most calcium has been found in the ash of oak trees that grew in calcium-deficient soil.
A mulch of oak leaves serves to control radish and turnip maggots as well as repelling slugs, cutworms, and grubs of June bugs, but some gardeners believe the leaves have an inhibiting effect on certain vegetables. Therefore they should be fully composted before being spread on the garden.
In Germany it has long been a practice to control greenhouse pests such as ants, aphids, and small mites with the smoke from oak leaves. The smoke is not considered poisonous and will not kill bacteria in the soil, nor leave harmful residues.
Live oaks are believed to exert a protective influence on citrus trees.
The trichogramma wasp, whose larvae feed on moth eggs, helps keep oak trees green by controlling gypsy moths. Bacillus thuringiensis (see the Pest Control chapter) will also control and kill various caterpillars on the trees.
This thorny tree is native from Arkansas to Texas and is hardy as far north as New England and central New York. It is valued for windbreaks or to grow in poor soils, and is an excellent hedge plant, being almost impenetrable when fully mature. It was widely planted by the pioneers as a living fence around their homes before barbed wire came into use. The name refers to the Osage Indians and to the yellow fruit, which looks like an orange but is inedible.
Pine boughs are good to lay over peonies in winter for protection. Remove them in the spring before growth starts. Pine needles make a good mulch for azaleas, rhododendrons, and other acid-loving plants and will increase vigor and flavor in strawberries.
Pine needles contain terpene, which, washed down by rain, has an inhibiting effect on seed germination. It is not good to place a compost heap near pine trees.
The quick-growing, short-lived poplar often fulfills the function of “nurse tree.” When a fire sweeps through the forest, it is likely to be the first tree to grow again on the bare land. The poplar’s abundant seed, much like willow’s, is wind-sown far and wide. Lombardy poplars, which look like exclamation points, are often planted to shelter other plants from the wind.
In Canada, very good stock feed has been made by boiling poplar wood under pressure.
This “hippy” rose has become so famous that it deserves to be mentioned all by itself. Grown in a mass, it makes a charming windbreak as well as an almost impenetrable barrier for animals. It grows better with purslane, parsley, and mignonette around it; is protected from rose bugs by alliums or onions nearby. Keep boxwood away. It blooms prolifically and is an excellent source for berries (hips) rich in vitamin C, containing more than oranges. The hips are used for making teas, jams, soups, and other dishes.
Rosa rugosa
All the alliums — garlic, onions, chives, and shallots — are beneficial to roses, protecting them against black spot, mildew, and aphids. For a recipe to overcome black spot in roses, see Tomatoes in the Vegetables chapter.
Garlic and onions are particularly beneficial to roses. In Bulgaria, where attar of roses is produced for perfumes, it is a common practice to interplant them with roses since they cause the roses to produce a stronger perfume in larger quantities.
Roses also are aided by parsley against rose beetles, by onions to repel rose chafers, by mignonette as a ground cover, and by lupines to increase soil nitrogen and attract earthworms. Marigolds are helpful against nematodes, and geraniums or milky spore disease against Japanese beetle. (See Milky Spore Disease in the Pest Control chapter.)
A carpet of low-growing weeds from the Purslane family will improve the spongy soil around the roots of rosebushes. An infusion of elderberry leaves in lukewarm water sprinkled over roses is thought to control caterpillar damage and is also recommended for blight.
Do not plant roses with other plants that have woody, outspreading roots that will compete with the roses for soil nutrients.
Sassafras is sometimes called the mitten tree from its peculiar leaves, which grow in three different shapes: the simple ovate leaf, a larger blade (oval in form but with one side extended and lobed to form a thumb), and third, a symmetrical three-lobed leaf, the pattern of a narrow mitten with a thumb on each side.
Sassafras will repel mosquitoes. The pungent oil has antiseptic properties, and the bark mixed with dried fruit wards off insects.
Sassafras
A tea made from the bark of young sassafras roots has been used for digestive disturbances. The dried leaves, called file, were formerly much used in the southern states as an ingredient in soups. However, sassafras is now regarded as unsafe for internal use.
Three species of woodpeckers were credited with controlling a serious infestation of spruce beetles in Colorado in 1947. Naturally occurring Bacillus thuringiensis (see the Pest Contol chapter) has been found to give good control of this beetle in some forests.
Studies conducted by American and Iraqi scientists show that sycamores inhibit the growth of other herbaceous plant species, and the decaying leaves cause significant reduction in seed germination and seedling growth. Organic compounds leached from the leaves often are allelopathic to plants, and virtually no herbaceous plants will grow under the trees.
Sycamore bark has value, however. Boiled in water and made into a poultice, it is good to use for poison ivy.
The wild bird, pine, or red cherry grows from Newfoundland to Georgia and west to the Rocky Mountains in rocky woods, forming thickets that are valuable as nurse trees. Wild cherry often springs up in burned-over districts where its bird-sown pits take root, the young trees sheltering new pines and hardwoods. It provides berries for birds and nectar-laden flowers for bees, so it can scarcely be called worthless, even though it is a short-lived tree.
The wild black cherry (P. serotina) is sometimes called the rum cherry. A tonic is derived from its bark, roots, and fruit, and brandies and cordials are made from its heavy-clustered fruits, which hang until late summer, turning black and losing their astringency when fully ripe. The wild black cherry makes an attractive shade and park tree, too.
The wild black cherry and the chokecherry (P. virginiana) are both of value to attract birds. Unfortunately, the tent caterpillar favors them to lay its eggs, making the trees unpopular with farmers. The egg rings in the outer smaller branches are easily seen and removed.
The tough and fibrous roots of willow are useful in binding the banks of streams that may erode. Nature seems to have designed them specifically for this purpose, for wherever a twig lies upon the ground, it will strike root at every joint if the soil is sufficiently moist. The wind often breaks off twigs and the water carries them downstream where they lodge on banks and sandbars, which soon become covered with billows of green.
For thousands of years the bark and leaves of the willow have yielded resins and juices that eased the aches and pains of rheumatism and neuralgia or alleviated the distress of fevers. In the 1820s, salicin, the active principle of willow bark, was isolated, and in 1897 a synthetic derivative gave the world aspirin.
Before planting a windbreak, study your land carefully and plan to put it where it will do the most good. Consider prevailing wind directions and the location and relationship of your buildings to the area you want protected. Most often windbreaks are planted across the west and north sides of a property, but of course there are exceptions to this rule, depending on the configuration of the land and the winds.
Do not plant your screen too close to the garden, for if the windbreak is to consist of trees and shrubs, they will rob the soil of moisture and nutrients. If you have sufficient land, plant the windbreak at least 50 feet from field crops. Very possibly you do not have this much room, but be as generous as you can.
The protective factor of a windbreak is 20 times its height. Thus a 10-foot screen would give you protection up to 200 feet downwind from it. You will also receive protection for several feet in front of the tree belt because it causes the air to back up and act as an invisible wall before it hits the planting of trees. Not the least of its uses is to hold down soil against heavy winds and to keep snow from drifting over walks and driveways. It may even help you to reduce fuel bills.
In the prairie regions in particular, shelterbelt plantings have a marked influence on local climate, especially if they are placed at right angles to prevailing winds. A chain of such belts checks movement of the air, slowing down the wind velocity even before the windbreak is reached, and starts up a whole series of favorable climatic influences. These influences, such as a reduction of evaporation by increasing the humidity of the air, improve the yield of crops grown under their protection. (See Hedges in this chapter, and Vertical Gardening in Garden Techniques.)
The witch hazel is a stout, many-stemmed shrub or small tree, characteristically an undergrowth of larger trees. Native Americans were the first to use the bark of the witch hazel for curing inflammations. An infusion of the twigs and roots is made by boiling them for 24 hours in water to which alcohol then is added. The extract distilled from this mixture is used for bruises and sprains and to allay the pain of burns.
Perhaps the alcohol is the effective agent, for chemists have failed to discover any medicinal properties in either bark or leaf — yet who knows, they may still find it.
The tree has the peculiar property of throwing its seeds, particularly in dry, frosty weather. This does for the parent tree what the winged seeds of other, taller trees accomplish.
Witch hazel gets its name from the fact that superstitious English miners once used the forked twigs as divining rods.