CLIMATIC CONDITIONS FAVORABLE AND UNFAVORABLE TO THE RAISIN INDUSTRY.
Limits of the Raisin Districts.
—It is an interesting fact, and by no means a coincidence, that the raisin districts of the world are found on or between the same latitudes. Thus we find the California districts between latitudes 32°, 75´ and 38°, 75´. The latitude of Smyrna is 38°, 28´, 7´´, that of Malaga in Spain 36°, 75´, Valencia 39°, 25´, Denia 38°, 50´, the Grecian Islands and Morea 37° and 38°, and finally Huasco in Chile 28° south latitude. That the latter place is situated so much farther south or so much nearer the equator cannot exactly be considered exceptional, as it conforms with the general characteristics of the Southern hemispheres as compared with those on the northern half of the globe. In Europe the Muscat grape for raisin purposes is not a success north of the fortieth degree of latitude. While the limits in California and Chile are not yet fully ascertained, it may be presumed that, as far as regards this country, these limits will not differ very much from those of Spain and Asia Minor. Only years if not centuries of experience will finally decide where and where not raisin grapes can be grown and cured to perfection. While the vines and the grapes can be grown in many places, the proper curing of the raisins is attended with more or less difficulty in the various districts. With proper modes of curing the grapes, and by protecting them from the inclemencies of the weather, the limits of the successful raisin districts may be extended considerably both north and south.
Dry Seasons, Spring and Fall Rains.
—The climate of the Mediterranean basin, as well as of the raisin districts of the New World, present the peculiarity of having only two distinct seasons, one dry and warm, and one cold and wet. There are other parts of the world also characterized by a dry and a wet season, for instance Mexico and Central America, etc., but they differ in the important point, that whereas the climate of the raisin districts is dry during the growing or summer season, Mexico has then its greatest rainfall. While grape-growing may not be impossible under such circumstances, the curing and drying of raisins is impossible, except with the aid of costly and burdensome appliances, the expense of which will very much increase the cost of producing the raisins. The climate of the raisin centers is by no means uniform. As a rule, the farther north we go the less is the distinction between the dry and the wet season, the shorter is the former and the longer the season of rain. Experience shows that the less this distinction between the seasons is marked, and the shorter the rainless season, the less favorable is the climate for the raisin industry. The longer the dry season, and the less rain during the same, the more favorable is the locality for raisin drying and curing, supposing, of course, other necessary conditions are not absent. This absence of summer rains and cold fog is the most important climatic condition, and the one that more than any other decides upon the advantages of any certain locality for the industry under our consideration. A perusal of the reports from the different raisin districts will convince us of this. For California we need not refer to any special reports, as the newspapers are full of them every year from May to November, and it will suffice to state that any large amount of rain after the beginning of June, and especially in September, October and November, when the raisins are curing, is considered very detrimental, and sure to cause much loss. Heavy and continued rainfall during the drying season would not only injure the raisins, but might even totally ruin the crop. Any district where year after year such showers occur, would not be considered favorable for the raisin industry, and would no doubt be given up to something else. To show that these same conditions also exist in the Mediterranean raisin districts, we will here quote a few extracts from the United States consular reports from there. Consul W. E. Stevens, United States consul at Smyrna, writes:[5] “It happens occasionally that rain falls during the vintage time, causing heavy loss to growers through the inevitable deterioration in quality. This was the case last season (1883), and large quantities of raisins were in consequence shipped to France to be made into spirits.” From Valencia another consul writes: “In the event of wet and damp weather, the hurdles (or grape mats) are piled up in sheds covered with mats or painted canvas. Of course in this case the drying is retarded, the quality of the fruit deteriorates, and the expense and labor of curing are considerably increased.” Two years ago ten thousand tons were thus damaged in the Denia district. While the Mediterranean districts are comparatively rainless during the summer time, still they are far less so than California. The rainy and dry seasons there are less distinct than with us.
[5] Consular Reports, No. 411⁄2, June, 1884, page 745.
Among the Grecian Islands, the production of currants is confined to only a few localities, principally on account of the untimely rainfall on the other islands. Dr. Davy (Ionian Islands, page 320) tells us: “The attempts to extend the culture of the currant to some other islands have been only partial, and attended with doubtful success. This, it is to be understood, is not owing, as has been asserted, to any unfitness of the soil on other islands, as it is analogous on them all, but rather to some difference of climate, especially about the times of ripening, gathering and drying of the fruit, consisting in greater liability to rain, a heavy fall of which is ruinous to the crop, and which, during the period of gathering in the currant islands, is considered a great calamity.” But even in Zante and Cephalonia in Greece, the crop is sometimes greatly injured on account of rain. Thus in 1857 a crop of fifty thousand tons was expected, but disastrous rains in August injured the raisin grapes to such an extent that seventeen thousand tons were totally destroyed, and twelve thousand tons became unfit for anything else than distilling. Malaga in Spain, which of all the districts most resembles California, has undergone similar experiences, both damaging and ruinous.
It is thus that the fall rains are everywhere feared the most, the more so where they may be expected with regularity, and where the district is so situated that the heat of the sun is not powerful enough to rapidly dry the injured crop. Thus in Valencia the rains are feared more than at Malaga. In the latter place the sun is powerful enough to dry the raisins, and only repeated showers would injure the crop. Our experience is very much the same, and the early fall rains in the northern part of the State are to be feared much more than rains at the same time farther south, where a few showers would soon be succeeded by warm weather, and a hot sun powerful enough to dry the partially cured grapes. On account of local conditions, certain parts of Central California are freer from these fall rains than the more southern districts, but this disadvantage is counteracted by the greater amount of warm weather and drying winds just at a time when they are most needed. But while the southern part of the State is in this respect not as favorably situated as some other parts, the disadvantage is greatly counteracted by the warmer and drier fall weather in October and November, and by drying winds which are often able to desiccate the moistened raisins in a very few days.
Spring rains in May or even in the early part of June cannot be considered greatly detrimental to the vines. On the contrary, if only occurring at long intervals, one or two showers say during the season, they are rather beneficial than otherwise. In California I have never known them to injure the crop, except if accompanied by heavy hail. Much alarm is regularly felt every time such a shower happens to come, but after it is well over it will generally be found that the vines look fresher and better, the ozone and ammonia which was brought down by the rain having acted as powerful fertilizers for the grape-leaves, and increased their vigor and growth. The only thing that might prove injurious at this or any other time of the growing season would be continued cloudy weather before or after such showers, which would cause mildew. Such weather has to my knowledge never been experienced. Occasionally spring rains also bring frost, and this of course is one of the greatest enemies of the raisin-vines.
Winter Rains.
—In order that the raisin grapes may develop and mature without the aid of irrigation, the winter rains should be sufficient to keep the soil moist during the dry months. The absolute quantity of rain thus necessary varies in different localities. In California, generally, we would say that from twenty to twenty-four inches of rain would be required every year to keep the soil sufficiently moist to grow Muscatel grapes without irrigation. The nearer we go to the coast the less rainfall is required to supply this moisture, and the farther we go inland, the more elevated the land, the less rain is needed. Thus a regular rainfall of twenty-four inches would possibly not suffice on the low plains of the San Joaquin valley, while in El Cajon in San Diego county one-half of this rainfall is enough to grow the vines and mature small crops of very good and superior grapes.
It matters not from where the moisture comes,—from rain, seepage, moist air or irrigation,—as long as it is not present in excess nor too scant. In El Cajon valley the moisture appears to be held in suspense in impervious strata, or perhaps in strata which contain and preserve the moisture as does a sponge. In parts of Chile, as well as in Malaga and Smyrna, the winter rainfall is sufficient to grow crops of fair size and good quality, but it is almost certain that judicious irrigation in any of these places proves beneficial and remunerative. Of all the present raisin districts, Smyrna enjoys the greatest rainfall, often as much as thirty odd inches of rain. Of localities which grow raisins profitably with the least possible amount of rain, and without irrigation, Huasco and El Cajon take the lead. In Central California, as well as in San Bernardino county, no raisin culture would be possible with the natural rainfall. In foreign countries, Valencia and the Grecian Islands, as well as Morea, are similarly situated in not having sufficient rainfall to produce paying crops.
As a rule it may be said that, where the rainfall is sufficient to grow the Muscats without irrigation and cause them to bear good crops, the fall rains are also too frequent and too injurious to the drying grapes to allow a profitable raisin cult. The proper amount of moisture necessary to perfect the grapes cannot be ascertained by the aid of the rain gauge. While, as we have said, from twenty to thirty inches may be enough in Smyrna, from seven to ten inches suffice in El Cajon, and in Chile even less is required. The proper amount of moisture can best be told by the state of growth of the vines. The vines must have moisture enough to be kept growing up to the very time of the maturity of the grapes. The proper sign of this is the green and fresh color of the young shoots or the tips, combined with a certain vigor of the tendrils. When the tips cease to grow, and the tendrils begin to dry up, then the moisture has begun to give out, and irrigation should have been resorted to; the winter rains were not sufficient.
Frosts in Spring and Winter.
—One of the frequent effects of spring showers is spring frosts. They are always injurious to the tender Muscat vine, and if occurring more than once during the same spring may entirely ruin the crop. In California such frosts occur sometimes in April, and observations inform us that they are most to be feared between the tenth and fifteenth of that month, while sometimes they come even later. The young buds are then either opening or fully developed into shoots, which the lightest frost will blacken and cause to dry up. Where the vines are irrigated and strong, one such frost may not ruin the crop, as new buds will start out in place of the old ones destroyed, and new shoots and new blossoms will come out. I have seen as many as three such crops of shoots develop from the winter buds, but each succeeding crop of such shoots is weaker than the preceding one, and bears less and later grapes. Happily, these frosts occur but very seldom in the Central and Southern California raisin districts, and during fifteen years of observation I have seen only three such frost years in which the branches were partially injured. In neither of these seasons was the crop materially injured as to quantity, the principal effect of the frost being a retarding of the crop for a week or more. Smoking of vineyards can only be successfully carried out in small valleys sheltered from heavy winds, but on the open plains such smoking is accompanied with difficulties, and its effect is uncertain. The growing of a limited number of windbreaks has in the Fresno district no doubt modified the climate, and made spring frosts rarer and less to be feared.
While the spring frosts are injurious to the grapes, winter frosts are on the other hand most beneficial, if not necessary to a continued raisin cult. The raisin grape must have a season of recuperation, and winter frost is the only climatic phenomenon which, without injury to the vine, can procure it that rest which is so necessary for all deciduous trees, by nature destined to enjoy alternate periods of growth and sleep. The absence of frost causes the sap of the vine to circulate more or less in the wood, and the vine never ceases to grow. This is one of the reasons why our deciduous vines do not succeed well in the tropics, where there are no cold seasons to cause the leaves to fall and the sap to become dormant. In the tropics, therefore, our deciduous vines keep on growing, set little or no fruit, and prove unprofitable. This phenomenon is shared there with other trees, and peaches, pears and apples act in the same manner. They all appear to need the rest afforded them by the winter frosts. It is also a question of very great importance, whether the continued and unnatural activity of the vine, at a time when it should be dormant, does not invite diseases of various kinds, which find the exhausted vines unfit to withstand their ravages. It may be possible that mal nero, the vine plague and other similar and as yet insufficiently understood diseases, are especially destructive to vines growing in frost-free climates, while in colder climates they make but little headway, the vines as it were being protected by the heavy frosts, which either kill the enemies of the vine or enable the latter to gather the necessary strength to battle with them through the growing season. There can be little doubt that at present the healthiest vineyards are those growing in countries where winter frosts are severe, but on the other hand we know that grapevines have been growing for ages in temperate climates, where the frosts, even if not entirely unknown, are still of very rare occurrence.
Summer Temperature.
—The temperature in summer time must be sufficient to properly ripen the grapes, but must not be so great as to injure them either while they hang on the vines, or while they are exposed to dry on the trays. The average heat required to do the work of maturing is not exactly known, but it is certain that a very high degree is not absolutely needed to produce sweet grapes. As far as our experience goes, it seems that cool weather, with the average temperature of ninety degrees Fahrenheit, would be most beneficial in the fore part of the season, while when the grapes begin to ripen a greater heat is desirable. It is not the warmest countries nor the warmest seasons which produce the earliest grapes. Thus while the season of 1888 was in California unusually cool, with the thermometer seldom reaching one hundred degrees in June and July, the raisin season was nevertheless a very early one, and much earlier than seasons remarkable for their early high temperature. In Malaga and Smyrna, the heat seldom reaches one hundred degrees, and the grapes ripen several weeks earlier than in Fresno, where the summer temperature averages ten degrees higher. In Fresno, on the contrary, the season is earlier than in Southern California, where probably the seabreezes retard the ripening of the grapes. A temperature of over one hundred and five degrees proves injurious to unprotected or exposed grapes in the central region of California, but in San Diego county several degrees less is sufficient to scald the grapes or give them a cooked flavor if they are already exposed on the trays to dry. It is certain that with an average highest temperature of ninety degrees, the grapes develop better and become larger and sweeter than where the heat is excessive and reaches one hundred and ten degrees or more.[6]
[6] Whenever the temperature is referred to it means the degree of heat (Fahrenheit) in the shade, and not in the sun except when so expressly stated.
The time when the greatest temperature occurs is of practical importance. Excessive heat can be tolerated by grapes protected by leaves and branches or otherwise sheltered, but if it happens at a time when the bunches are exposed to dry on the trays, the injury to the berries will be great or even ruinous. Early localities are especially apt to suffer in this way, and it is well to experiment before too much confidence is placed in very early regions. To such places, however, there remains the possibility of curing the raisins in partial shade, as is done in Chile, thus producing raisins of an entirely different type from the Malaga or California product.
Winds, Injurious or Beneficial.
—In the California raisin districts hot, electrical winds are much feared in the months of June and July, or before the grapes have begun to ripen. In the San Joaquin valley these winds come from the northwest and sweep down over the vines, often scorching the leaves and frequently drying the berries on the exposed side. In the course of a few days the berries dry up entirely, and the whole bunch is lost. These drying winds are not peculiar to any certain part of California, but occur from time to time in every raisin district on the coast, in the south as well as in the center, on the coast as well as inland. The remedy is to grow the vines low and to keep the berries well covered. The planting of windbreaks will also modify these winds, and in places where they formerly were common they have now entirely ceased or become so modified that they cause no injury to the grapes, but prove even beneficial on account of the quicker and better maturing of the fruit. In certain districts, especially in San Bernardino and in Orange, some very drying winds are experienced late in the season,—in September and October. For the raisin-growers these winds are a blessing. They quickly dry the exposed grapes, which have been retarded in drying, or perhaps even injured by a previous shower of rain or by continued heavy dews. These winds are undoubtedly desert winds, and similar to the Terral of Malaga, which, sweeping over the inland plains of La Mancha, reach the coast vineyards and quickly mature the grapes. In Malaga there is also a moist southern wind, the Levante, which retards the ripening and the curing of the grapes, and which must be considered as our southwesterly fall winds, which, saturated with moisture, swell the overdried raisins as well as prevent the yet green grapes from drying. They are precursors of the rainy season, and warn the grower to prepare his dryer if he possess one. In Greece and Smyrna such hot or moist winds are also known and feared, and cause at times much damage in one way or another. We might here also mention the cold “northers” which are common in the California raisin districts in springtime, and which sometimes both cause the young shoots to break off from the old wood and make it easy for the mildew to attack the flowers or the young berries of the vines. Against these northwest winds we have two remedies, summer pruning and sulphuring, which, if applied in time, are both quite effective.
Fogs and Moisture in the Air.
—It is certain that the air in the California raisin districts is much drier than that of the Spanish or Mediterranean districts generally. The night air is, in these districts, loaded with moisture, and dew is heavy and frequent, even in the middle of the summer. The air in Malaga and Smyrna feels quite moist, and without this moisture in the air the vines would grow less and require irrigation. In these places the raisin grapes grow on the steep hillsides without irrigation, but in California this could not be done anywhere except in El Cajon or in other parts of the San Diego district, where the air is considerably moister than elsewhere. This increased moisture is partly caused by the increased rainfall in these districts, and partly by their nearness to the sea and fogs. This moisture in the air will, when other conditions are equal, greatly benefit the grapes, causing them to grow larger, and the thickness of the skin is materially diminished. Combined with this moisture in the air, fogs are injurious or indifferent. There is always a great difference between warm fogs and cold fogs, and now I speak principally of fogs from the ocean. Warm fogs are not particularly injurious to the grapes, generally indifferent and sometimes even considerable of a benefit to the proper development of the grapes. In Malaga, San Diego and in Chile the Muscat grapes grow and thrive actually within the reach of the spray of the waves, and fogs are there not uncommon, but they are warm. It would seem that such a climate would cause mildew or oidium, but I cannot find that these fungi are particularly frequent in San Diego county, while in Malaga they are but little more common than in the inland districts of our State. But as we go north the cold fogs become more common, and the vines thrive less under their influence. North of Los Angeles county the Muscat vines do not enjoy the coast air, while even in Orange county the interior vineyards are preferred to those closer to the coast. But anywhere, even in the best situated districts, protection from the direct influence of the sea fogs is appreciated, and the best localities are those in which low hills afford this protection by modifying and increasing the temperature of the fog or sea air.
In Central, and in the larger part of Southern, California, the inland valleys are the most successful raisin-producing districts, while even in San Diego county, where the Muscats seem to thrive at the very seashore, the interior valleys alone afford the necessary heat and dry air for curing the grapes and transforming them into raisins. According to Consul G. H. Heap of Constantinople, the positions preferred for vineyards in Turkey are the slopes of elevated and sheltered undulating lands, or on the sunny hills that do not lie too near the coast, or are naturally protected from the cold winds and fogs of the sea. The Island of Cos or Zea is called the paradise of the Sultana grape, because Nature has given the cultivable land there the best possible protection from the direct influence of the fogs. In Malaga, according to Consul Marston, eighty per cent of the vineyards are situated on the hills and inland, ten per cent on the valley lands or plains, and ten per cent on the coast. With the exception of some of the San Diego vineyards, California cannot show any raisin vineyards as close to the coast as those found in Malaga. The main El Cajon vineyards are from ten to fifteen miles inland, while the former Santa Ana vineyards were situated from eight to twelve miles from the coast. The San Bernardino raisin vineyards are from twenty to thirty miles inland, while in the San Joaquin valley the raisin districts are more than a hundred miles from the coast, while the sea wind, before it reaches any of the vines, has been modified by passing over from two to three hundred miles of dry country.
Ideal Conditions of Climate.
—There remains only to draw some conclusions from the above facts. We are often asked what are the ideal conditions, as far as climate is concerned, for the proper development of the raisin grape, and for the proper curing of the raisins. Could we select such an ideal spot, where all the requirements for the raisin industry could be found in their highest perfection, with as few of the drawbacks as possible, our choice would be as follows: A moderately dry air, a frostless spring, a rainy winter and a rainless autumn. The temperature in the summer should vary between ninety and one hundred degrees, the fall months should now and then be visited by drying winds, while the winter frosts should be heavy and regular, but not below twelve degrees. Some have suggested that absolute freedom from any rain would be very desirable, as then no interference would be experienced with the cultivation of the grapes, but I doubt if the soil in such districts would not be rapidly exhausted through the want of weeds, the plowing under of which enriches the ground and enables it better to preserve the moisture provided for it by irrigation.