This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
The date seems to enjoy not only a high atmospheric temperature, but a high temperature of the water supplied in irrigation as well. In irrigating small crops by flooding, it is necessary in midsummer to irrigate late in the afternoon or at night in order to prevent scalding. Care should be taken, in the hotter part of the year, that the date palm is not subjected to hot water about the roots, rising above the soil for a considerable length of time, and later left until the soil becomes exceedingly dry and baked by the sun. Such extremes sometimes seriously injure or destroy the tree.
The date palm comes into bearing early, examples being known in California of fruits being produced two years after the seeds were planted. It usually requires six to eight years, however, for seedlings to bear any considerable quantity of dates. Under the best date-culture, seedlings are not used but the plants are propagated by means of suckers, as already explained; these suckers soon become established and will bear abundantly in five or six years afterwards. After ten or fifteen years, the palm may be considered to be in full bearing and should continue to produce indefinitely. It should yield 100 to 200 pounds of fruit annually, although there are cases -of -very much higher yields than this. To conserve the strength of the parent plant, the suckers should not be allowed to grow around the base in large numbers. Usually not more than three or four of these suckers or offshoots are allowed to remain at any one time. After the palm is in full bearing and has a trunk a few feet high, the offshoots cease to be produced. It is recommended, however, that one offshoot be left attached to the mother plant in order to replace the tree in case of an accident.
If the date palm is allowed to grow as it will, it becomes a clump of many trunks, surrounded by a jungle of offshoots.
It is advised that the date palm be planted at distances of not less than26 to 33 feet. Other crops can be grown between the trees till they come into bearing heavily, or even continuously.
Under proper cultivation, the date palm should produce from ten to fourteen leaves each year. A well-developed tree will have at one time from thirty to sixty leaves, the old ones dying away below while new ones are forming at the top. The different varieties show great variation in rapidity of growth, form and length of leaves, size of stem, and general aspect of plant. The stem of the date palm is very rigid. When the stem reaches a height of 5 or more feet it is frequently necessary to tie the growing bunches of dates securely to the lower leaf-stalks, that they be not broken and injured by the wind before maturity.
While it is possible to produce dates by depending on wind-pollination from male to female trees, this process is much too uncertain for commercial culture and requires a very large number of male trees. In commercial plantations, one male tree to 100 females is sufficient; but this requires that the pollinating shall be performed by hand. Small separate twigs or branch-lets of the male inflorescence, from 4 to 6 inches long and bearing thirty to fifty flowers, are tied on the female cluster. Inasmuch as the .flowers in the female cluster mature at different times, it is necessary to repeat the operation of pollination. In old plantings, persons must climb the trees in order to perform this operation, but for the first ten or fifteen years of bearing the clusters are so near the ground that little if any climbing is required. Each female flower produces three ovaries. After pollination, two of these ovaries fail and one matures into the date. In case there is no pollination, all three of the ovaries will develop but will be seedless and the fruit will be inferior.
Fig. 1225. An American seedling date.
As with other fruits, it is often necessary to thin the dates on trees, particularly on young trees that tend to overbear. Even on old trees, best results are to be secured if only eight or ten bunches are left.
Usually the dates in an entire bunch do not ripen at the same time. Picking off the dates as they ripen is a practicable operation when labor is cheap. In general, however, it probably will be found the better plan to cut the entire bunch at once. This may require some special operation in the handling and curing. Some varieties require practically no special handling or curing and are ready to ship as soon as they have ripened naturally. Usually, however, the bunch must be ripened much as a bunch of bananas is cured, by being cut off and hung in a moist and warm place. It has been found that in Arizona the best varieties of dates may not ripen naturally on the tree. Freeman's experiments at the Arizona Experiment Station show that conditions favorable for the rapid . ripening of the Deglet Noor may be produced artificially in an oven. The degree of moisture and temperature may be carefully regulated. In this ripening process, there is not only a change in the sugar-content but the tissues of the date are softened, the tanin is precipitated and the astringency of the fruit is thereby relieved. Vinson found that dates may be ripened artificially by means of chemical reagents.
Artificial ripening by means of heat, moisture, and chemical stimulation makes possible the production of commercial crops at altitudes too high and cool to mature many medium and late varieties. Losses by rain, insects, and birds are minimized, and greater cleanliness secured. Last year over half the crop from miscellaneous varieties'at the Tempe Date Orchard (Arizona) would have been lost but for artificial methods of ripening. These methods are cheap and practicable. In connection with ripening operations, the fruit can be pasteurized at a temperature of 65° to 70° C (149°-158°F.) and then packed under cheese-cloth to secure it from contamination by flies and other insects. Recent experiments by Drummond show that fumigation with carbon bisulfide kills insect eggs, and is preferable to pasteurization with varieties inclined to be sticky. In 1910, Swingle discovered the process now in use for ripening Deglet Noor dates by keeping them in moist atmosphere in closed packing-boxes which are kept warm at night and heated to 80° or 90° F. during the day. Deglet Noor dates ripen perfectly by this process and remain light-colored while those ripened by the rapid process are darkened.
Freeman's rapid process will ripen greener dates, however.
Fig. 1226. Fruit clusters of date, as grown in Arizona.
For further discussion, see Phoenix; also the bulletins of the United States Department of Agriculture, and of the experiment stations of Arizona and California.
J. W. Toumey L. H. B.†