Methods of Keeping Plants Healthy and Unharmed
Many cultural practices have as their objectives the protection of plants from conditions and enemies that are likely to harm them. Among the most important of these are excessive cold, too-high temperatures, sun, snow, water and wind, as well as diseases, insects, birds, animals, humans and weeds.
Protection from damage by humans is usually best achieved by means of effective fencing; thus a hedge or other barrier, suitably placed, may prevent harm from being done to a lawn by people walking across it and forming worn paths, and the likelihood of damage being done to planted areas by automobiles.
Fences afford good protection, too, against damage by the larger domestic animals such as cattle, sheep, horses, hogs and dogs and against some wild animals, especially deer and rabbits. To be effective, fences must be strong and of sufficient height. To protect trees and shrubs in winter this means fences sufficiently high above the surface of any snow that may accumulate on the ground. Fences must also be impenetrable by the particular animals they are to keep out. To keep out rabbits, chicken wire having a half-inch or three-quarter-inch mesh is practicable.
To keep the bark of trees from being gnawed by animals such as rabbits and mice (this is especially likely to occur in winter) encircle the trunks with a guard or a girdle of galvanized-wire hardware cloth or half-inch mesh chicken wire. The girdle should extend to a depth of about 6 in. beneath the ground level and sufficiently far above the ground to prevent the animal from reaching unprotected bark when a thick layer of snow makes it possible for it to reach far higher than it otherwise could.
Certain bulbs, such as Crocus and Tulip, are especially likely to be eaten or otherwise damaged by rodents such as mice, chipmunks and moles. These pests may be circumvented by planting the bulbs inside baskets or cages made of wire mesh, or by surrounding the whole bed with a vertical wall of the same material carried to a depth of 8-9 in. below ground and extending an inch or two above ground.
A bed in which bulbs are to be planted is lined with wire mesh.
Baskets made of wire-mesh hardware cloth may be sunk in the ground and bulbs planted in them to protect them from mice.
Trapping is the effective way of controlling damage by squirrels, chipmunks, mice, rabbits, moles, woodchucks and other animals, but gardeners should carefully check local laws covering these practices before engaging in them. Only traps of humane types should be used, and they should always be placed where neither persons nor domestic animals, wild animals and birds that are not pests will be harmed by them. In some cases, permission to shoot or trap can be obtained from the State Game Warden after lodging a complaint with him of the damage done.
Against cats, dogs, deer and some other animals, repellents that may be sprayed on the plants have some limited value. Their disadvantage is that they must be frequently renewed. Commercial preparations are available from dealers in horticultural supplies.
Crows, English sparrows and a variety of other birds may harm gardens by damaging fruit, picking off buds, scratching up seedbeds, and in other ways, so that sometimes it is necessary to curb them. Care should always be taken not to destroy birds that are harmless or that in general are useful even though they occasionally damage a little fruit or scratch up a few seeds. Most birds are desirable in gardens and more than "pay for their keep" by aiding in suppressing insects and other pests; they also delight the eye and ear. Check carefully before taking steps against them.
Trapping is the best way of eliminating birds that must be controlled, but check local laws carefully before attempting this. If proper precautions are taken, poisoned grain may sometimes be used effectively, but, unless carefully handled, it is very liable to endanger the lives of desirable birds, animals or even of children. None of these means are practicable against domestic birds such as chickens and ducks. Fencing is the only satisfactory means of keeping these out of gardens. Scarecrows and other bird scares are sometimes effective in keeping birds away.
Small areas, such as seedbeds, or even a few fruit bushes, may be protected from the attentions of birds by enclosing them in cheesecloth, fine netting or metal screening. As some insurance against injury, the maintenance of bird feeding stations and the provision of drinking water has much to recommend it; some birds damage garden crops when other sources of food are lacking and take juicy young buds and soft fruits to quench their thirst.
Protection from Sun and Heat
The gardener must at times give plants protection against too intense light and against excessively high temperatures.
Damage from intense light is most likely to occur when naturally shade-loving plants are exposed to direct, strong sunshine; when sun-loving plants, comparatively soft and tender from being grown in a greenhouse or cold frame, are transferred outdoors; and after plants are transplanted. The trunks of trees that have been growing closely together in woodland or nursery may be damaged by sunscald on their south-facing sides following their transference to sunnier locations; by heavy pruning, branches previously shaded by foliage may be exposed to sunshine sufficiently strong to sunscald them. Damage by sun occurs not only in summer; in winter, when the ground is frozen, evergreens, especially, are likely to suffer from this.
The provision of shade is the obvious method of avoiding damage by light that is too intense. Shade-needing plants should be grown in naturally shaded areas, such as woodland, under solitary trees or groups of trees, and areas shaded by high walls or buildings or in locations artificially shaded by lath houses, lath or burlap screens or other appropriate means.
The trunks of trees may, with advantage, be wrapped in burlap or in special tree-wrapping paper for a season or two following transplanting. When annuals, vegetables, young biennials and perennials are set out in hot sunny weather they should be shaded for a few days following the transplanting operation.
Not a great deal can be done to lower summer temperatures; but in every garden some locations are noticeably warmer than others. At the base of a south-facing wall, for example, the temperature is very noticeably higher than at the base of a north-facing wall; it is likely to be cooler near a pool or other body of water than elsewhere; parts of the garden that receive reflected heat from walls and pavements are warmer than those where plants grow alone in more open areas; in enclosed, "pocketed" spaces temperatures are higher than in more open locations through which breezes blow; and in the shade it is always much cooler than in the sun.
In selecting locations for plants known to prefer cool summer conditions, all these factors should be borne in mind. It should also be remembered that moisture has a cooling effect, and so plants should not be permitted to suffer from lack of water during dry weather.
As a temporary measure, shading may be used to offset some of the ill effects of temperatures that are too high. Spraying the foliage lightly with water lowers its temperature somewhat and has a refreshing effect on plants.
Flowerpots, with a stone placed under the rim of each to ensure ventilation, are here used to shade newly planted annuals.
Many plants—Clematis and Lilies, for example —can withstand high atmospheric temperatures, provided the soil is kept reasonably cool and moist. In really hot weather an even temperature at the roots and a steady supply of water go far to ensure success with a great many kinds of plants, especially those that are surface-rooters such as Azaleas, Blueberries and Rhododendrons. Summer mulching is an excellent garden practice designed to conserve moisture and keep the soil temperature moderate and even.
Summer Mulching. An even temperature around the roots and a steady supply of moisture in the soil are all-important to growing plants. A mulch, applied in early summer after hot weather begins, tends to maintain these conditions as well as to control harmful weeds.
Mulch materials suitable for summer use are numerous, and the choice will often depend on which is most easily or most economically obtainable. Among kinds commonly used are tobacco stems, peat moss, buckwheat hulls, salt-marsh hay, straw, strawy manure, coarse compost, and leaves (preferably Oak or Beech or a mixture of various kinds, although Pine needles form an excellent mulch beneath Pine trees and around really acid-soil plants). Sawdust may also be used, in which case an application of a fertilizer containing nitrogen should be made at the same time. Pebbles, gravel or rock chips are employed as mulch materials in rock gardens. Flat stones are sometimes used around individual difficult-to-grow plants that revel in a cool root run.
Newly planted trees and shrubs benefit from being mulched immediately after planting. This practice conserves soil moisture, promotes root growth and reduces the likelihood of the plants' suffering from lack of moisture during their first summer.
In winter, low temperatures as well as too intense light, lack of water (when the soil is frozen the moisture in it cannot be absorbed by the roots), and wind may cause damage. Some harm is directly due to the effects of below freezing temperatures on the tissues of tender plants; other damage is indirect—for example, the tearing and drying of roots that follows heaving of the soil as a result of alternate freezing and thawing.
It is well known that plants in poorly drained soils are more susceptible to winter killing than specimens of the same kinds growing in well-drained places. Plants located in hollows or "frost pockets" are much more likely to be damaged than those planted where there is free air drainage. Selection of favorable planting sites is important as a protection against damage by cold.
Importance of Fall Watering. Trees and shrubs, particularly evergreen kinds, are less likely to suffer winter damage if the soil in which they grow is kept moist throughout the autumn. If this is done, their tissues go into the winter well supplied with moisture and they are better able to withstand the dehydrating effects of sun and wind when the ground is so cold that it is difficult or impossible for them to absorb adequate supplies of needed moisture.
If fall rains are inadequate, evergreen shrubs should be soaked thoroughly each fall before the soil freezes. A mulch of leaves or coarse compost applied immediately after the final watering is beneficial in cold climates.
Anti-transpirants. Where severe winters prevail much damage may be done to trees and shrubs, especially to evergreen kinds, by dehydration caused by their above-ground parts being exposed to the drying effects of sun and wind at times when their roots are in frozen soil or in ground so cold that absorption of moisture is prevented or retarded.
An effective way of reducing damage of this type is to spray the foliage at the beginning of severe winter weather and once or twice more at about monthly intervals with an anti-transpirant (anti-dessicant) liquid. Such sprays based on rubber latex or plastics are sold by dealers in garden supplies under various brand names.
Anti-transpirants are of especial value when used on evergreens growing in exposed locations and for use on specimens that have recently been transplanted.
Mulching for Winter Protection. Very fine protection against cold is provided if an insulating layer of more or less loose material is spread over the surface of ground occupied by the roots of many plants. Such a layer either may prevent the underground portions of the plants from freezing or may simply prevent the ground from freezing as deeply as it otherwise would. In the latter case, at least some of the roots are likely to be in unfrozen soil and, if the plant is evergreen, it may still absorb at least some moisture to compensate for that lost from the aboveground foliage.
Winter mulching is really resorting to Nature's way of protecting plants. When leaves fall they are blown among shrubs and other perennial plants. Before they decay and return plant food to the soil, they serve as a protection for roots and other below-ground parts by keeping a more even temperature in the soil over which they lie. Many gardeners, instead of taking a lesson from Nature, are inclined to neatness and artificiality and so rake up these leaves in fall. This is not always good practice. If it is done, in many areas it is desirable to replace them with a winter mulch.
Small shrubs, especially those that have been recently planted or are not reliably hardy, can be protected by placing a layer of dry leaves, several inches thick, around them. The leaves should not be packed down so that air is excluded but should be left loose. Chicken wire may be used to contain them and prevent them from being blown away.
Larger shrubs and evergreens benefit greatly from having the soil covered with a 3-6 in. layer of half-rotted compost, loose, strawy manure, half-rotted leaves or any other appropriate mulch material that remains fairly loose and does not pack down and exclude air.
Winter Covering. In part, this term is interchangeable with winter mulching, but not wholly so. Winter covering includes the various types of protection that cover the tops, the above-ground portions, of plants. Winter covering is normally removed with the coming of spring; winter mulches are often left in position to decay gradually and form nourishment for the plants, or are forked into the ground to decay beneath the surface.
Among plants that are winter covered in cold regions are trees, shrubs and evergreens likely to be injured by cold, perennials and bulbs likely to be damaged by low temperatures and deep freezing of the soil, and young or newly transplanted specimens that may be harmed by heaving of the soil due to alternate freezing and thawing.
Young plants of many perennials and biennials are not thoroughly winter hardy in all regions. Where they are somewhat tender, or where there is danger of the small plants being heaved out of the ground by alternate freezing and thawing, they are benefitted by a light winter covering. Plants such as Foxgloves and Canterbury Bells that retain their foliage during winter will not survive, however, if a heavy layer of winter-covering material is spread over them. It should be just thick enough to shade the soil, and so check too frequent alternate freezing and thawing. Branches from Pines, used
Branches of evergreens or discarded Christmas trees provide effective winter protection for perennials.
Christmas trees or other evergreens are very satisfactory as a winter covering, as also is salt-marsh hay.
Delphiniums are sometimes protected by having sand or coal ashes heaped around and over their crowns. This is especially worth while in gardens that suffer from excessive moisture.
Irises and Peonies may not need winter protection if they were planted early. However, young plants set out rather late in the season may suffer injury from heaving by frost unless it is prevented by a light covering. This is especially desirable if the soil is clayey.
Bulbs. Some hardy bulbs such as Daffodils (Narcissi) may suffer damage from severe frost if they are planted late in beds or borders. They should therefore be planted as early as obtainable or be covered with 4-5 in. of straw, salt-marsh hay, leaves, branches of evergreens or similar material. Hardy bulbs planted in grass sod do not require this protection.
Bulbs that are on the borderline of hardiness in any given region, and even many that are usually regarded as tender, may survive the winter outdoors if they are covered. For nearly hardy kinds, those that are just slightly tender —as, for example, Brodiaea uniflora, the Spring Starflower, in southern New York—a covering 4-5 in. thick of any of the materials recommended above for hardy bulbs will prove sufficient. For more tender kinds—such as Gladioli and Montbretias, in southern New York—a layer about a foot thick will usually enable them to survive by preventing the frost from striking deeply enough to harm them. Even Dahlias may be kept alive through the winter by this method in regions where they would otherwise surely perish.
When winter covering is used, it is important not to put it into position too early, not until the ground has frozen to a depth of an inch or two, and it should be removed gradually, not all at one time in spring. If put on too early, many winter-covering materials attract mice and other rodents that may take up winter quarters under their protection; these are likely to damage the plants. Too early or too rapid removal in spring may result in severe damage to tender shoots by sun, wind and late frost.
Shelters and Wrappings. In addition to materials laid directly upon the ground or the plants, there are types of winter covering that involve building a shelter of burlap or similar material about the plants and wrapping the aboveground parts in hay, straw, paper and other protective materials.
Evergreens, even kinds considered fairly hardy, are much more susceptible to winter injury than are leaf-losing (deciduous) trees and shrubs. They transpire moisture through the leaves in winter as well as in summer, and protection from high winds and bright sunshine may be very necessary in cold regions, especially for those evergreens that are not natives. Burlap, neatly nailed to 2 by 4-in. supports on the exposed sides of the plants, is helpful. A few branches of Pines or other evergreens stuck in the soil so that they give protective shade may be all that is needed for some of the smaller, growing evergreens liable to winter damage.
Deciduous trees and shrubs, the tops of which are somewhat tender, as are, for example, Fig trees and Hydrangea macrophylla rather farther north, may be successfully brought through the winter by tying their upper parts together, wrapping them in a thick layer of straw, hay, newspaper, old blankets or other material that provides good insulation, and encasing the whole in a layer of waterproof building paper. This is done before very hard frost, and the covering is removed in spring after danger of severe frost has passed.
Roses. In regions of cold winters Roses need protection. Hybrid Tea and Floribunda bush Roses will withstand a temperature of about 12 degrees F. but are likely to be damaged by alternating mild and cold spells. They can be protected by mounding soil, buckwheat hulls, or peat moss around the base of the plants, covering them to a height of at least 8 in. Where the temperature drops below zero F., they should have soil mounded up to them and, after the ground is frozen to a depth of an inch or two, a thick covering of strawy manure or leaves should be placed over this.
Tree or standard Roses will tolerate about 15 degrees F. Where temperatures drop below this, they should be laid along the ground and covered with soil and a layer of leaves, straw or other winter covering. In the most northerly regions they must be lifted and buried in a trench in the ground.
Large-flowered and everblooming climbers will survive at 5 degrees F. but are best mounded as recommended for Hybrid Teas where the temperature goes lower. In colder regions it is safest to lay the shoots down on top of the ground and cover them with soil.
Climbing Hybrid Teas and Floribundas should be mounded with soil in similar fashion and, in colder regions, laid down along the ground and covered with soil and mulch.
Wintering Plants Indoors. It is common practice to protect many tender plants by growing them over winter in greenhouses, window gardens and in cold frames. In the former locations the plants usually continue to grow through the winter and need attention in the matters of watering, fertilizing and other cultural care in order to flourish.
Plants wintered in cold frames grow little or not at all until warm spring weather arrives.