This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
The article which follows consists of extracts from "Farmers' Bulletin 324" of the United States Department of Agriculture, and is by W. It. Beattie of the Bureau of Plant Industry:
* With the passing of each year the sweet potato is becoming of greater importance as a commercial truck crop in the United States. During a long period it has formed one of the principal sources of food for the people of the Southern States and of tropical America. As a commercial truck crop the sweet potato would be included among the five of greatest importance, ranking perhaps about third in the list. As a food for the great mass of the people living in the warmer portions of our country the use of this crop is exceeded by hominy and rice only. In many of the islands of the Pacific, especially in the Philippines, the sweet potato is the principal vegetable food for large numbers of the lower classes, at certain seasons being almost the only food available.
The sweet potato industry in this country is readily divided into two classes of production: (1) For home use and (2) for market. A quantity sufficient for home use can be grown under a wide range of conditions, while production on a commercial scale is somewhat restricted by climate and soil and also by market and transportation facilities. The larger Eastern markets are now well supplied, but there are sections where the people have not as yet become accustomed to the use of sweet potatoes in large quantities. The field for the production and use of sweet potatoes is very broad, and this crop promises to become of more general farm importance.
In view of the constantly increasing interest in sweet potatoes it is the purpose of this bulletin to give simple cultural directions covering their production both for home use and for market, including the soil and its preparation, the propagation of the plants, planting, harvesting, storing, and marketing, together with the uses of sweet potatoes for stock feeding and for similar purposes.
The sweet potato is of a tropical nature, its original home probably being the West Indies and Central America. The true sweet potato, as we have it growing in the United States, belongs to the morning-glory family, its botanical name being Ipomoea botatas. Throughout the Southern States the sweet potatoes having moist flesh are commonly known as 'yams' and those having dry flesh as sweet potatoes. The name 'yam' is misleading and properly belongs to a distinct class of plants that are confined almost entirely to the tropics.
Owing to the tropical nature of the sweet potato it naturally thrives best in the South Atlantic and Gulf Coast States, but it may be grown for home use as far north as southern New York and westward along that latitude to the Rocky Mountains. The areas suited to commercial production extend from New Jersey southward and westward to Texas, and are found again in the central valleys of California. In the Mississippi Valley the commercial area extends as far north as the southern part of Iowa, Illinois, and Indiana. The region around Louisville, Ky., is noted for excellent crops of sweet potatoes.
Sweet potatoes thrive on a moderately fertile sandy loam which does not contain an excess of organic matter. They are frequently grown upon almost pure sand, especially where the subsoil is a yellow clay. Soils containing considerable calcium or underlain with limestone are well adapted to the growing of the crop. The sweet potato is exceptional in that a fairly good crop can be grown upon soils that are too poor for the production of the majority of farm crops. Sweet potatoes yield a fair crop on the 'wornout' tobacco and cotton lands of the South, especially when used in a rotation including some leguminous crop for increasing the humus in the soil.
The more common varieties of the sweet potato have for a great many years been propagated by cuttings, or sets, taken either from the potatoes themselves or from growing vines, and as a result the plants have ceased to flower and produce seed. The greater portion of the commercial crop is grown from sets, or 'draws,' produced by sprouting medium-sized potatoes in a warm bed of soil. In the Southern States the seed potatoes are frequently cut into pieces in the same manner as Irish potatoes and planted in the row where they are to mature. Where several plants appear in one hill they are thinned, and those removed are used for planting other land. In the South Atlantic and Gulf Coast States the sweet potato is frequently propagated by making vine cuttings. A comparatively small bed of seed potatoes is planted quite early and the sets so produced are used to plant a small patch from which vine cuttings are taken later by the cartload for planting large fields. In the southern parts of Florida and Texas and on the South Sea Islands the potatoes may remain in the soil from year to year, being dug only as required for use, those remaining over producing the sets for the following season's planting.
In the warmer portions of the sweet-potato-growing district the seed should be bedded when danger of frost has passed. In the northern portion of the area the seed should be placed in the hotbed from the 20th of March to the 10th of April, after the temperature of the bed has fallen to 80 degrees or 85 degrees F. and become regular.
As a general rule sweet-potato plants are set in the field shortly after a rain. In order to avoid delay in planting, the hands should begin to get out the sets as soon as the rain ceases falling and place them in crates or baskets ready for transportation to the field. The sets are not all produced at once, and only those that have formed good roots are ' drawn,' the others being left until later. In 'drawing' the sets the seed potato is held down with one hand while the plants are removed with the thumb and finger of the other hand. It often happens that five or six plants will cling together at the base, and these should be separated in order to avoid loss of time in the field. Where plants are to be set with a transplanting machine it is essential that they should be in the best possible shape in order that they may be handled rapidly by the boys who feed the plants into the machine. The roots should all be kept in one direction, and if the tops are long or irregular they may be trimmed off even by means of a knife.