Greater care than is usually bestowed should be given to the selection of the peanut seed. In addition to following the principles given in Section XVIII, all musty, defective seeds must be avoided and all frosted kernels must be rejected. Before it dries, the peanut seed is easily injured by frost. The slightest frost on the vines, either before or after the plants are dug, does much harm to the tender seed. [Illustration: FIG. 202. A PEANUT PLANT] In growing peanuts, thorough preparation of the soil is much better than later cultivation. Destroy the crop of young weeds, but do not disturb the peanut crop by late cultivation. Harvest before frost, and shock high to keep the vines from the ground. The average yield of peanuts in the United States is twenty-two bushels an acre. In Tennessee the yield is twenty-nine bushels an acre, and in North Carolina and Virginia it reaches thirty bushels an acre. SECTION XL. SWEET POTATOES The roots of sweet potatoes are put on the market in various forms. Aside from the form in which they are ordinarily sold, some potatoes are dried and then ground into flour, some are canned, some are used to make starch, some furnish a kind of sugar called glucose, and some are even used to make alcohol. The fact that there are over eighty varieties of potatoes shows the popularity of the plant. Now it is evident that all of these varieties cannot be equally desirable. Hence the wise grower will select his varieties with prudent forethought. He should study his market, his soil, and his seed (see Section XVIII). [Illustration: FIG. 203. SWEET POTATOES] Four months of mild weather, months free from frost and cold winds, are necessary for the growing of sweet potatoes. In a mild climate almost any loose, well-drained soil will produce them. A light, sandy loam, however, gives a cleaner potato and one, therefore, that sells better. The sweet potato draws potash, nitrogen, and phosphoric acid from the soil, but in applying these as fertilizers the grower must study and know his own soil. If he does not he may waste both money and plant food by the addition of elements already present in sufficient quantity in the soil. The only way to come to reliable conclusions as to the needs of the soil is to try two or three different kinds of fertilizers on plats of the same soil, during the same season, and notice the resulting crop of potatoes. Sweet potatoes will do well after almost any of the usual field crops. This caution, however, should be borne in mind. Potatoes should not follow a sod. This is because sods are often thick with cutworms, one of the serious enemies of the potato. It is needless to say that the ground must be kept clean by thorough cultivation until the vines take full possession of the field.