reprinted from Cyclopedia of American Horticulture by L.H. Bailey, 1902
SWEET POTATO. Ipomoea Batatas. An edible tuberous root, much prized in North America, a staple article of food in all the southern states, and also much consumed in the North. The Sweet Potato plant is a trailing vine of the morning-glory family. The branches root at the joints. The edible tubers are borne close together under the crown and unlike the common potato they do not bear definite “eyes.” The varieties differ greatly in length of vine and the “vineless” Sweet Potato has a bushy habit. Good commercial varieties that are well cared for rarely bloom, and even then the flowers may not produce seed. The plant is tender to frost. The species is widely distributed in tropical regions but is supposed to be of American origin. It has been cultivated from prehistoric times by the aborigines. The plant is exceedingly variable in its leaves, and the varieties are sometimes classified on the foliar characters. In the southeastern states the word “potato” usually means sweet potato, the potato of the North being known as “Irish,” “round” and “white” potato.
(Turn of the Century) The Sweet Potato crop amounts to fifty million bushels annually. Large quantities are grown in the Carolinas, Georgia, Texas, Alabama, Mississippi, Virginia and New Jersey, the last state being the farthest point north where the crop is raised on a large scale. In California the yield is also large, particularly in the interior valleys and in places removed from the influence of the coast climates. The Sweet Potato is propagated by means of its tubers, usually from the slips or cuttings, which arise when the tubers are planted in beds or frames. It is also propagated by means of cuttings or slips taken from the tips of fresh runners. A bushel of ordinary Sweet Potatoes will give from 3,000 to 5,000 plants, if the sprouts are taken off twice. An average good yield of Sweet Potatoes is 200 – 400 bushels per acre. Yields twice as high as these are sometimes secured.
In the northern states amateurs occasionally grow Sweet Potatoes of the southern types in a small way on ridges in the garden, but it is usually for the pleasure of the experience rather than for profit. A warm, sunny climate, long season, loose warm soil, liberal supply of moisture in the growing season and a less supply when the tubers are maturing – these are some of the requirements of a good Sweet Potato crop. The crop should be gathered immediately after the first frost. In the South a soft and sugary Sweet Potato is desired. In the North a firm, dry, mealy tuber is the prevalent type. Certain varieties of Sweet Potatoes are called “yams” in the South, but this name belongs historically to a very different kind of plant, for an account of which see Dioscorea.
COMMERCIAL CULTIVATION OF THE SWEET POTATO
The cultivation of the Sweet Potato as a staple crop is confined almost exclusively to the southern states. While it is true that the Sweet Potato occupies large areas in New Jersey and is also planted more or less extensively throughout portions of Illinois, Indiana and Ohio, by far the greater bulk of the crop is to be found below the 38th parallel of latitude. Hence the cultural details here given, as well as the memoranda on diseases, are compiled from a strictly southern standpoint.
Methods vary but little. Local environment enters less as a factor into Sweet Potato culture than into any other horticultural industry of the country. For this very reason it is remarkable that there should occur such extraordinary variations in type as are everywhere noted, and for which local environment, if anything, should be held responsible. So marked are these variations that without apparent cause any given “variety” so-called – more correctly, perhaps, “selection” – will develop, when transferred a few hundred miles from its place of origin, after a few years of cultivation in the hands of half a dozen different growers, just that many distinct types, each differing materially from the original in its more important characteristics – productiveness, maturity, quality and habit of growth. This difference extends, sometimes, even to a change in the form of the leaf itself from possibly an ovate shape with margin entire and with no more trace of a lobe than an apple leaf has, to a sagittate or halberd form or even to one deeply cleft or indented.
Propagation is effected altogether by means of shoots, mostly those from the root. While blooms are often found on the vines – particularly in the extreme South – they are nearly always imperfect and invariably drop from the pedicel. No ovaries ever develop. Therefore the remarkable series of rapid transformations observable in the Sweet Potato must be credited entirely to an active and persistent tendency in the plant to bud variation – in effecting which it must be admitted to be a veritable kaleidoscope.
Propagation. – “Draws,” or developed sprouts from root-buds, supply the readiest and, indeed, the only practicable means of propagation. Tubers of the last season’s crop are “bedded” for this purpose; that is, an outdoor hotbed is constructed in which the tubers are placed in a single layer, close together, and covered with several inches of soil early in spring. In a few weeks the latent buds of the tubers, under the stimulus of the heat from the fermenting manure, will have sprouted, and by the time all danger from frost has passed a dense growth of “draws,” or “slips” will cover the bed. These are removed from the tubers, set by hand in the field in rows four feet apart – the plants eighteen inches, generally, in the row. The size of the bedded tubers does not affect the crop. As good results are obtained from small as from large potatoes. Even the smallest tubers or “strings” consistently planted from year to year, produce as heavily as the choicest selections. This is but logical if we remember that the Sweet Potato is merely and enlarged, inaxial, fleshy root, and heavy tubers, when sprouted, should have little direct tendency to produce a crop of corresponding size, particularly when the subsequent cultivation is indifferent.
For later plantings the “bed” may be supplemented by cutting “slips” 12 or 14 inches long from the young vines after growth commences in the row, and using them as “draws.” While the “slips” do not live quite so readily as the rooted “draws,” they are said to make smoother and more sightly tubers – due, doubtless, to the fact that by this method the mycelium of the black rot is not conveyed from the bed to the field.
Soil and Fertilization. – Although a gross consumer of nitrogen, the Sweet Potato cannot advantageously occupy “bottomland.” With this reservation it may be said that almost any land will produce potatoes. Yet a light, sandy loam is best. Stiff, red soil is to be avoided, as in it the potato splits, cracks and “roughens,” by reason of the suspension and sudden resumption of growth during variable weather.
Cottonseed meal has been found in many localities preferable to sodium nitrate, as it is not so readily soluble and therefore more gradual and continuous in action through the season. It may be substituted in the formula for sodium nitrate in the ration of two pounds for one. Potassium muriate produces as heavy a crop as potassium sulfate, but the latter considerably increases the starch content, which in southern-grown potatoes is unusually large. For potash, kainit may be substituted in the proportion of four pounds of kainit to one of either potassium sulfate or muriate. Stable manure of normal composition produces excellent Sweet Potatoes, but is, of course, too variable in character and too uncertain in quantity to be generally available.
A complete summary of methods employed in Sweet Potato culture would occupy too much space. They are, moreover, too familiar to require repetition. Yet it is desirable to call special attention to certain points which have been insufficiently discussed in previous publications. First among these is the practice of premature planting. Against this tendency earnest protest should be entered. It is the cause of much loss. When an early market crop is not the object there is no need for haste in putting out the draws, since the season is abundantly long for leisurely planting, even in June, after oats and wheat are harvested. If planted in May, or earlier, with the long southern season, the crop is likely to mature before the approach of cold weather permits the proper housing. The consequent and usual result is a “second growth,” which predisposes the tubers to the inroads of the “soft rot,” which causes great loss.
A deep, mellow soil-bed, with an extended season, unquestionably will produce more and larger, but later, tubers. Shallow preparation will yield an earlier crop. It follows that the deeper the soil the earlier the planting may be effected.
Preservation. – Were it possible to successfully and inexpensively preserve through the winter the Sweet Potato crop, southern agriculture would be practically revolutionized. Land capable of producing a bale of cotton will readily yield 300 bushels of potatoes, at half the cost for cultivation. Methods, too, are variable in the rule of uniformity and prevailing in Sweet Potato culture. Climate and local environment seem here to play an important part, and means of preservation found successful in one place prove entirely unserviceable in another – personality, even, entering as a factor in the problem, one man failing where another, by the same methods, succeeds. Many ways have been devised and practiced, some simple, some elaborate; but each said by its enthusiastic originator or advocate to be absolutely infallible.
Nothing has yet been found that will effectually supersede the well-known popular method of “banking” or “hilling” in quantities of from 30 to 50 bushels, according to the different local customs which prevail in each community. The ordinary practice is to heap the tubers in a conical pile around a perforated wooden flue, covering them with a few inches of dry pine-straw, then a layer of corn stalks, and finishing with three inches of dry sand and afterward two or three inches of clay or other stiff soil. The hill may be constructed either under shelter or out-of-doors. If the latter is well to protect with a covering of boards to keep off the rain, though not absolutely necessary.
Diseases and Maladies. – A few of the most important maladies of the Sweet Potato – the cause, indeed, of nine-tenths of the loss experienced in attempts to winter the crop – will be noted in the probable order of their importance:
(a) Soft Rot (Rhizopus nigricans): This is the most common form of rot, and the one that produces the most damage. It is due to a fungus or mold on abraded places, chiefly of the tuber, especially when the potatoes are stored in large bulk, without sufficient opportunity to dry out. It is perhaps the main cause of loss with stored potatoes, developing rapidly and immediately, under favoring conditions, and reducing, sometimes in a few weeks, the entire contents of a bin or hill to a pulpy mass of corruption, emitting a most disgusting odor. A few simple remedial measures will greatly reduce loss from this cause: (1) Dig only when soil is dry. (2) Dig before tubers become sappy from a “second growth.” (3) Remove all affected tubers before storing. (4) Use padded baskets in handling to avoid abrasion. (5) Store in small bulk and keep dry and well ventilated.
(b) Black Rot (Ceratocystis fimbriata): The fungus producing this affection does not depend so much on the conditions of moisture and abrasion, and is slower in making its appearance than is the soft rot, continuing to develop, however, all through the winter and often completing the destruction the other has begun. It is all the more to be dreaded because it is not so immediately noticeable, and tubers containing its germs are more likely to be housed. The black rot does not produce a pulpy mass, though effectually destroying the entire tuber. It frequently makes its appearance on the young draws at “setting out time.” Remedy: careful selection 1st. of sound tubers for bedding; 2d, of perfectly healthy draws for setting; 3d, where these conditions cannot be fully complied with, by planting the bulk of the crop with cuttings from the vines, thus minimizing the damage. The use of copper sulfate, or any of the standard fungicides, either as a spray or for soaking the tubers, is not advisable; for, since the mycelium of most of the fungi causing decay in the Sweet Potato is lodged in and protected by the interior cells of the tuber, surface treatment would prove more or less futile.
(c) Soil Rot (Acrocystis Batatas): This fungus, as its name implies, is a resident of the soil rather than of the tuber, and hence cannot be readily guarded against. It is responsible for most of the decay observed in the crevices or cracks of split tubers. Sudden expansion of vegetable tissue due to a resumption of rapid growth when wet weather follows a period of drought, particularly when the soil is a stiff clay, produces the primary “cracking” and the spores of the fungus, finding a ready lodgment, start the process of decay. As for remedies, heavy applications of sulfur to the soil have been found to checks its ravages in a measure, but this method of operation is not practical. That is to say, while checking the fungus the result is not commensurate with the cost. The surest preventive – and this is true for any and all rots – is rotation. The same areas should never be planted in potatoes two years in succession, nor should the same spot be used twice for a hotbed to furnish draws, even at the cost of great inconvenience in establishing the bed in another place.
(d) Other fungi: Several other fungi are serious enemies of the Sweet Potato, as the stem rot, white rot, dry rot, potato scurf, leaf blight, etc.; but their ravages will not compare with the damage produced by the first three – soft rot, black rot and soil rot.
As for the first three, it matters little to the practical grower whether or not he is able to distinguish one from another. After the conditions favoring the spread of one of them have been permitted to develop and the resulting decay once appears, it is usually too late to put remedial measures into effect. Remedy, in this case, must precede manifestation of disease. Every possible precaution should be observed at one and the same time against them all. Proper preventive effort during harvesting will be found a surer guarantee against loss from decay than the most elaborate structure or the most carefully detailed method of housing yet devised and when thoroughly enforced little apprehension need be felt as to results, no matter what plan of preservation is adopted.
To this end the following summary of procedure will be found serviceable:
- a. Rotate the crop. Never plant twice in succession on the same land.
- b. Rotate the bed. Never use old soil or old manure a second season.
- c. Dig only when the soil is dry.
- d. Dig before tubers are rendered moist and sappy by a “second growth,” and to this end never plant too early in spring.
- e. Use padded baskets in handling to prevent bruising and abrasion.
- f. Handle with scrupulous care.
- g. Reject all affected tubers before storing.
- h. Store dry, in small bulk; if in bins erect bulkheads and use flues for ventilation.
- i. Use only perfect tubers for bedding, rejecting any showing symptoms of decay.
- j. Use only healthy and unaffected draws for setting out.
- k. When draws in bed are affected with diseased root (black rot) and cannot be thrown away, plant in a separate plat and take cuttings from their vines later for the main crop.
Varieties. – Since new varieties of the Sweet Potato can originate only by bud variation, it is a marvel where and how all of the different types arise. The writer has personally cultivated and tested some fifty odd kinds, and there doubtless exist, in all, 75 or 80 – the number still increasing. But one uniform method of classification exists – that by the “leaf” into tribes, falling under the three heads, “Leaves entire,” “Leaves shouldered or lobed” and “Leaves cleft” – commonly termed “round – leafed,” ”shouldered” and “split-leafed,” respectively. Of these the second type is the most numerous, containing probably two-thirds of the entire list.
As for the best variety, the “all-round” potato has not yet been found, nor is it likely to be, since such a type should be a tremendous yielder, of first quality, a safe keeper and free from disease. No potato embodies, superlatively, all of these characteristics. All of the heaviest yielders belong, unfortunately, to the “milky” or “turpentine” group – as Norton, Hayman, Southern Queen, White St. Domingo, Early Golden, etc., – and their sappy consistency prevents them from keeping well, while their quality, is uniformly poor. Regarding quality however, tastes differ. The northern market prefers a dry, mealy potato, represented by the Jersey or Nansemond strain. The southern market, on the other hand, demands a rich, sugary potato, like the Georgia or Yellow Yam, which is generally considered to be the standard of excellence, and is a good keeper though yielding very lightly.
The market it is intended to supply should, therefore, be specially planted for. If for northern shipment, the Jersey Sweet is preferable. For early local sale Orleans Red, Early Golden or Bermuda Red, head the list. For winter storage and local market in spring it is best to rely on the good old popular standard – the Georgia Yam – despite its light yield, or reinforce it with Vineless, which closely approaches it in quality and is a much heavier cropper.