American Pomology. Apples

by J. A. Warder

It may be asked: How do these masses of water affect the frost? Science answers: By their evaporated moisture influencing the atmosphere. This may save us from the blighting influence of frost, by enveloping the frozen vegetation in a wet blanket of fog; enabling it to be thawed in the dark, as it were, by which we avoid the influence of a bright sunshine, that would have destroyed the tissues had they been suddenly exposed to it when frozen. An equally important result is derived from the direct influence of the humidity of the atmosphere, which modifies the temperature remarkably, as in the immediate vicinity of large bodies of water. Insular situations especially, even when low, are known to have a more genial climate in consequence of this condition of the atmosphere, which depends upon the large amount of caloric that is present in the latent form, in the vapor, and which becomes sensible heat as fast as the moisture is condensed; as well as by the sensible caloric, the absolute warmth of the water, affecting the temperature of the atmosphere.

We thus see that very opposite situations, in regard to mere elevation, may both be recommended for orchards; but the latter are the exceptions rather than the rule, for we can not always count upon the saving influence of a fog, nor are the modifying effects of a moderate sheet of water always to be depended upon at the time when most needed. Still, we may find a few favored spots, where an insular position, in a lacustrine situation, receives a double influence—acting at both extremities of the season of vegetation, in quite an opposite way, but in both acting favorably. In such places we shall discover that the spring opens late, being retarded by the cold atmosphere flowing over the chilled waters, that may be even icy, when inland places in the same latitude are rejoicing in a mild and genial temperature, tempting the expansion of the flower-buds. Vegetation on an island thus situated is retarded until all danger of frost has passed, and the air has received the full benefit of warmth from the water. Then, again, in the autumn, when we are in danger from the access of an early frost, such as sometimes, north of latitude forty degrees, destroys the whole crop of corn, almost universally, over hundreds of miles, these favored spots have really a warmer atmosphere, from the influence of a great extent of water, that has enjoyed a summer's sunshine, and which warms the air by giving off its heat very steadily, but slowly; and besides, as the surface of the land cools by radiation and condenses the watery vapor, it receives accessions of temperature that had been locked up, or was insensible in the vapor. Hence we find that in these places, though the opening of spring was retarded a month, the approach of winter and autumnal frosts is warded off for two months, making the season really one month longer than in the same latitude inland.

It must be confessed, however, that the subject of meteorology is not fully understood. We have but a glimmering of the light that we hope is to be shed upon the subject when the deductions from millions of observations, long continued and systematically conducted, shall have been wrought out for the benefit of the orchardist and the general agriculturist.

We also have storms accompanied by a low temperature, passing across the country, in which, at times, the greatest intensity of cold is at the southern border. Such a one passed from the west to the east in January, 1852, in which the mercury, near Marietta, O., sank to thirty degrees below zero; at Zanesville, O., on the same river, it was twenty-seven degrees; at Lancaster, O., thirty-two degrees; while at Cleveland, O., it was only fifteen degrees below, and at Aurora, on Cayuga Lake, N.Y., influenced by the unfrozen water, its greatest depression was only four degrees below zero.[20]

Aspect.—When considering the orchard site, the best aspect of the ground becomes a matter of interesting inquiry. To all vegetation, the morning sun is a welcome visitant after the night's repose; for plants, as well as animals, rest from their functions at night, and all nature rejoices in the return of day; hence an eastern or a southeastern exposure is generally preferred, but we find that practically there is little difference in the different parts of an orchard that can be fairly referred to this cause. Some planters prefer a southern slope, thinking that the fullest exposure to the sun is essential; others select a northern aspect, in the hope that they may there avoid a too early excitation of vegetable life, and also that the heats of summer may be thus moderated. In my own opinion, the aspect is a matter of little consequence to the success of an orchard, though my predilections are in favor of an easterly exposure. The danger of a southern aspect in summer, and the advantages of the northern slope, may, in a great degree, be obtained or obviated by judicious planting and pruning, as will be set forth in another place.

A theory has been started by those who are opposed to a northerly slope, that vegetation continues later in the season in such situations, especially with young trees, and that hence they are not in so good a condition to resist the access of very severe weather at the sudden setting in of winter. The hypothesis is not sustained by long-continued observation, although many facts noted in the autumn and winter of 1859 induced persons to embrace the theory; these were particularly the killing of the peach-buds, upon northern slopes, by the December frosts. There is no evidence that there was any want of perfect ripening of the wood in these situations; on the contrary, it is well known that, long before December, the growth of these very trees had been checked, the wood had been well ripened, and the foliage had been cast to the ground.

The warmer exposure of a southern slope may, and often does, favor the premature swelling of the buds and starting of the sap during mild, pleasant, and bright weather in the winter, and vegetation is often seriously injured from this cause.

In many parts of the country, it is much more important to consider the exposure to the prevailing winds of the region, and to select the site and aspect that shall enjoy the benefit of protection. This, I am aware, is a proposition that has had opponents; as well as advocates, in the broad savannas of the West, where, especially, it becomes a question of the greatest importance. There are benefits as well as evils attendant upon the motions of the atmosphere. The swaying of the limbs, when agitated by the breeze, gives them tone and strength, and may assist in the circulation of the sap within their cells; and the constant agitation of the atmosphere, commingling the warmer with the colder portions, will often modify the temperature to such an extent as to give an immunity from the frost in the open prairie, at the same moment that the more tranquil air, within a limited clearing of forest lands, has been cooled down, by radiation, to the frost point. On every account, therefore, the moderate and reasonable exposure to the influences of a mobile atmosphere is rather to be courted than shunned.

The views that have been advanced by the advocates of protection for orchards on the prairies, have been somewhat modified since they were first promulgated. We are now told, by those who have opposed "protection," that narrow timber-belts of evergreens and deciduous trees, should be planted on the windward sides of orchards, to moderate, not to cut off, the aerial currents; in this all will agree, and those who have any sympathy for a tree will surely prefer to have the blasts, that sweep over miles of open country, somewhat checked and tempered before reaching either themselves or their orchards. The testimony as to the effects of cold in sheltered and in exposed situations, it must be confessed, appears somewhat contradictory; but this is because we have not all the elements of a complex problem.

Winter-killing.—A most serious evil, both to the nurseryman and orchardist, is the severe injury sometimes done to the trees by frost. This is commonly known by the term "winter-killing," which has, at times, destroyed millions of trees, and thus blighted the hopes of long-continued labor and large investments of capital. Some orchardists have been disheartened, and have given up in despair. The investigation of the causes of this disaster, and the conditions under which it occurs, will be of great value to future planters; and though, perhaps, we have not yet at command sufficient data for the full explanation of the phenomenon, it may be well to look into the attendant circumstances that have been observed; and as some of the most important considerations depend upon the soil and exposure, they may be well introduced in this place.