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 climatic requirements for the
production of sweet potatoes on a commercial scale are (1) a growing
period of at least four and half months without frost, (2) warm nights
and abundant sunshine during the day, and (3) a moderate rainfall
during the growing period. Where irrigation is depended upon for the
supply of moisture, the greatest quantity of water should be applied
between the time the plants are set in the field and the time when the
vines practically cover the ground. If too much water is applied during
the latter part of the season the result may be an abundant growth
of vine and a small yield of stringy potatoes. For some time before
harvesting the crop the water should be withheld altogether, in order
that the roots may ripen properly.
_Soil._--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 "worn-out" tobacco and cotton lands
of the South, especially when used in a rotation including some
leguminous crop for increasing the humus in the soil. Like many other
crops, the sweet potato thrives on newly cleared land, but the crop
should not be planted continuously in the same place. With the sweet
potato, as with other crops, rotation is the keynote of success.
Good drainage is essential, the original idea of planting upon high
ridges being for the purpose of securing better drainage. The surface
soil should extend to a depth of 6 or 8 inches, and the subsoil should
be of such a nature that it will carry off excessive moisture without
leaching away the fertilizers applied to the land. Too great a depth
of loose surface soil or an alluvial soil having no subsoil will
produce long, irregular potatoes that are undesirable for marketing.
Planting upon land having a loose, sandy surface soil underlain by
a well-drained clay subsoil will tend to produce the type of rather
thick, spindle-formed potato that commands the highest price. The
depth of plowing is a prominent factor in the preparation of land for
sweet potatoes, and on soils of too great depth before the subsoil is
reached very shallow plowing should be practiced, leaving the soil firm
beneath, against which the roots must force their way. If the surface
soil is of insufficient depth, it should be gradually increased by
plowing a little deeper each year or by subsoiling in the furrow behind
the regular turning plow.
_Fertilizers._--The root portion of the plant is the part having the
greatest value, though the foliage and vines have some value as food
for certain kinds of stock. It has been found that an excessive amount
of organic matter in the soil will frequently produce an abundant
growth of vines at the expense of the roots. It has also been noted
that the potatoes will be small and the yield unsatisfactory on soils
that do not contain sufficient organic matter to produce a fair growth
of vine. The use of stable manure as a fertilizer for sweet potatoes
is recommended on lands that are deficient in organic matter. Heavy
applications of fresh manure shortly before planting the land to sweet
potatoes will stimulate not only the growth of weeds but also of the
vines at the expense of the roots. Well-rotted stable manure may be
used at the rate of 10 to 15 carloads to the acre, spread broadcast or
beneath the ridges and harrowed into the soil, but it is always well
to apply the manure with the crop grown the previous season. By this
method the manure will become thoroughly incorporated with the soil and
become somewhat reduced before the sweet potatoes are planted upon the
land. Stable manure will be found most beneficial on worn-out soils,
but on the more fertile soils its use should be restricted and the
method of application carefully studied.
The sweet potato is one of the few crops that thrive equally as
well (or better) upon commercial fertilizers as upon stable manure.
A fertilizer for use on the majority of sweet potato lands should
contain 3 to 6 per cent of nitrogen, 6 or 7 per cent of phosphoric
acid, and 8 to 10 per cent of potash. Every grower should make a study
of the requirements of his soil and apply the fertilizer that will
give the best results. Many growers purchase the ingredients and mix
their own special fertilizers, or use a standard fertilizer as a base
and increase the percentage of certain elements by adding high-grade
elementary ingredients. Some soils require that certain elements should
be in a more available form than others; in the case of nitrogen it is
often desirable to have a portion of that contained in the fertilizer
quickly available and the remainder more slowly in order to feed the
plants throughout the season. A mixture adapted to the growing of sweet
potatoes on most soils may be made by combining the following:
200 pounds of high-grade sulphate of ammonia, 25 per cent pure.
200 pounds of dried blood, or 300 pounds of fish scrap.
1,200 pounds of acid phosphate, 11 per cent pure.
400 pounds of high-grade muriate of potash, 50 per cent pure.
The quantity of fertilizer that may be profitably applied will be
governed entirely by local conditions. Many growers do not depend upon
commercial fertilizers, but merely apply from 200 to 300 pounds to
each acre as a supplement to the organic matter and natural fertility
of the soil. Others apply from 300 to 1,000 pounds, according to the
condition of the soil, while a few growers use a ton to the acre. The
general rule is to apply the fertilizer in the row where the crop is to
be grown, but where large quantities are used it should be distributed
at least ten days before planting and thoroughly incorporated with the
soil. An application of 1,000 pounds of high-grade fertilizer placed in
the row at planting time has been known to injure seriously or kill the
plants. For the best results the fertilizer should be applied at least
ten days before planting, or a portion of the fertilizer may be applied
a month or more in advance and the remainder at the time of preparing
the land for planting. Hardwood ashes are desirable for use on sweet
potato land and may be applied at the rate of from 1,200 to 2,000
pounds to the acre. The value of wood ashes depends upon how much they
have become leached, but hardwood ashes should contain from 6 to 8 per
cent of available potash. Wood ashes also contain considerable lime.
Where large quantities of any green crop are plowed into the soil there
is a tendency to sourness, and occasional applications of from 1 to 2
tons of lime to the acre are beneficial. The presence of an abundance
of lime in soils devoted to the growing of sweet potatoes hastens the
maturity of the crop and increases the yield. On poor soils the lime
and potash work together to produce potatoes of uniform size and shape,
but on rich or alluvial soils the tendency is toward the production of
over-large and irregular roots. The lime should be applied the previous
season, or at least the autumn before planting the land to sweet
potatoes.
_Propagation of Plants._--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.
Where only a small area of sweet potatoes is to be grown for home use,
the necessary plants can generally be secured from some one who makes a
business of growing them. If an acre or more is to be planted it will
in most cases be more economical to prepare a bed and grow the plants.
The method of starting the plants will depend upon the locality and the
acreage to be planted, the essentials being a bed of warm earth and a
covering to protect the young plants during the early springtime.
_Selection of Seed._--The potatoes that are to serve as seed from which
to grow the plants for the next season's crop should always be selected
at the time of digging and housing the crop. For seed purposes it is
the custom to select the medium or undersized potatoes, such as are
too small for marketing. Those potatoes that will pass through a 2-inch
ring or can be circled by the thumb and first finger of a man having a
hand of average size are used for seed purposes.
The seed potatoes should be uniform in size and of the shape desired in
the following year's crop. The seed should be free from cuts, bruises,
decay, or disease of any kind. Throughout the handling of the seed
potatoes they should not receive any treatment that would break eggs.
The seed should always be handled and kept separate from the regular
crop. The oftener the seed is handled the greater the danger of decay,
and it should not be sorted over until everything is ready for bedding.
The best seed is grown from cuttings taken from the regular plants
after they have begun to form vines. These cuttings produce large
numbers of medium or small-sized potatoes that are free from diseases
and adapted for use as seed the following year.
_Hotbeds._--Toward the northern part of the area over which sweet
potatoes are grown it is necessary to start the plants in a hotbed in
order that the length of season may be sufficient to mature the crop.
The roots that are too small for marketing are used for seed, and these
are bedded close together in the hotbed and covered with about 2 inches
of sand or fine soil, such as leaf mold. The seed should be bedded
about five or six weeks before it will be safe to set the plants in the
open ground, which is usually about May 15 or May 20. Toward the last
the hotbed should be ventilated very freely in order to harden off the
plants.
_Drawing the Sets._--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. 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. While drawing the sets it is a good plan to have at hand a large
pail or tub containing water to which there has been added a quantity
of clay and cow manure which has been stirred until it forms a thin
slime. As the plants are pulled from the bed they are taken in small
bunches and their roots dipped into this mixture. This process, termed
"puddling," covers the roots with a coating which not only prevents
their becoming dry in handling but insures a direct contact with the
soil when they are planted in the field or garden. After removing the
sets that are ready, the bed should be watered to settle the soil where
it has become disturbed and then left for the younger plants to develop.
_Packing for Shipment._--In preparing sweet potato plants for shipment
or for sale, they are "drawn" from the bed and tied in bunches of 100
each with soft string. Sweet potato plants will not withstand excessive
moisture and should always be packed while the tops are dry. A little
damp moss or paper may be placed in the crate or basket and the roots
bedded in it, but the tops should remain dry and have free ventilation.
If the roots of sweet potato plants are carefully puddled without
the mixture coming in contact with the tops, they will keep in good
condition for a week or ten days.
_Preparation of Land._--The character of soil devoted to sweet potato
culture is generally quite easy to prepare. In preparing land for
planting to sweet potatoes the plowing and fitting are practically the
same as for corn. It should be borne in mind, however, that the work
necessary for thorough preparation will be well repaid by the increased
ease in handling the crop later. It is always desirable that a crop
like sweet potatoes be grown as a part of the regular farm rotation.
In the northern portion of the sweet-potato-growing area the crop will
occupy the land the entire growing season, and a three or four year
rotation should be practiced. Where the climate will permit, a crop of
early snap beans, peas, or cabbage may precede the sweet potatoes, but
in any case the land should not be planted to sweet potatoes oftener
than once every three years. A good rotation is to devote the land to
corn one year, sowing crimson clover in the alleys between the rows at
the time the corn is given the last cultivation. During the following
spring the crimson clover should be turned under and sweet potatoes
planted; then in the autumn, after the potatoes are harvested, the
land may be plowed, fitted and sown to rye or winter oats with plenty
of grass seed. In this way a crop of grain may be obtained during the
time that the grass is becoming established. Allow the land to remain
in grass one or two years and then repeat the rotation. Where corn is
followed by sweet potatoes in the rotation, stable manure should be
applied while fitting the land for the corn, and commercial fertilizers
should be applied with the sweet potato crop.
The usual depth of plowing in preparing land for corn will prove
satisfactory for sweet potatoes. The fact that sweet potatoes are not
planted in the field until quite late in the spring makes it possible
for the grower to select a time when conditions are favorable for the
preparation of the land. Plowing may be deferred until the soil has
become sufficiently dry to break up fine and mellow. It is important
that the land should be harrowed within a few hours after plowing;
further fitting may be deferred until later, and if the soil is
inclined to be lumpy the work of pulverizing may best be done shortly
after a shower and while the lumps are mellow. When the primary work of
preparation is finished, the soil should be mellow to a depth of 6 or 7
inches and the surface smooth and even. Subsequent handling of the soil
preparatory to planting will depend upon whether ridge or level culture
is to be followed.
_Preparation for Planting._--After plowing and fitting the land it
is generally allowed to lie several days before being put in shape
for planting. If level culture is to be practiced, the only thing
necessary will be to run the harrow over the soil once and then mark
in both directions at the desired distances for planting. The marking
is generally done with either a one-horse plow, a flat-soled marker,
or a disk marker. The disk marker is well adapted to this work, as
it throws up a slight ridge which furnishes fresh earth in which to
plant. Some growers who practice level culture mark the ground with a
small one-horse plow and throw up a slight ridge upon which to plant;
behind the plow a roller is used to compress this ridge to a low,
flat elevation. Where the more universal ridge method of planting is
employed the soil is thrown up by means of a turning plow or a disk
machine. The ridges should be made at least one week before planting,
in order that the soil may become settled and compact. The majority
of sweet-potato growers make the ridges whenever the land is in good
condition to work and then either roll or drag the tops just ahead of
the planters.
_Setting the Plants._--The success of the crop depends largely upon the
way in which the plants start after being removed from the bed and set
in the field or garden. Practical growers always plan to set the plants
during a "season" or period when the conditions are suitable to a quick
start into growth, either just before a rain or as soon afterward as
the soil can be worked. The method of setting will depend entirely upon
local conditions and the acreage to be grown, the essential features,
however, being to get the roots in contact with moist earth and the
soil firmly pressed about the plants. The use of water around the roots
of the plants is desirable under most circumstances, as it not only
moistens the soil but assists in settling it about the roots. A large
quantity of water is not necessary, one-half pint to each plant being
generally considered sufficient.
Where level culture is practiced, the plants are set from 24 to 30
inches apart in each direction. On the eastern shore of Virginia the
greater portion of the crop is planted 24 inches apart each way,
requiring about 11,000 plants to an acre. By planting 30 inches apart
each way, only about 7,000 plants are required to set one acre. Where
the crop is grown on ridges it is customary to have the ridges from 36
to 42 inches apart from center to center and to place the plants 14 to
18 inches apart in the row. By this method an acre will require from
8,000 to 12,500 plants. An acre of good sweet potato land will readily
support 9,000 to 11,000 plants, and the number most commonly planted by
the several methods will fall within these figures.
_Cultivation._--The methods of handling a crop of sweet potatoes do not
differ materially from those employed with ordinary farm and garden
crops. Within a few days after planting, a sweep or one-horse plow
should be run in the alleys to break out the strip of earth left in
ridging. The loose earth in the alleys should be worked toward the rows
until a broad, flat ridge is formed upon which a small-tooth cultivator
can be run quite close to the plants. After each rain or irrigation
the soil should receive a shallow cultivation, and during dry weather
frequent cultivations are necessary in order to retain moisture. About
two hand hoeings are generally necessary in order to keep the rows
free from weeds and the soil loose around the plants. As hand labor is
expensive, it should be the aim to perform the greater part of the work
by means of horse tools. Where sweet potatoes are planted in check rows
and worked in both directions the hand work required will be reduced
to a minimum, but a certain amount of hoeing is always necessary. When
the vines begin to interfere with further cultivation the crop may be
"laid by," i. e., given a final working in which the soil is drawn well
up over the ridges and the vines then allowed to take full possession
of the land. To do this it is often necessary to turn the vines first
to one side of the row and then to the other by means of a stick or a
wooden rake. After "laying by," very little attention is required until
time for harvesting the crop.
_Harvesting._--The harvesting and marketing of sweet potatoes direct
from the field begins about the middle of August and continues until
the crop is all disposed of or placed in storage for winter marketing.
During the early part of the harvesting season the yield is light, but
as a rule the prices paid are good. The supply for home use and those
potatoes that are to be kept in storage should not be dug until just
before frost. In the localities where frosts do not occur until quite
late in the season the sweet potatoes ripen and the vines show a slight
tinge of yellow when ready for handling.
_Effect of frost._--The foliage of the sweet potato is very tender and
is easily injured by frost. A light frosting of the leaves will do no
harm, but should the vines become frozen before digging they should
be cut away to prevent the frozen sap passing down to the roots and
injuring them. Where there is a heavy yield of potatoes the soil is
frequently cracked or the ends of the potatoes protrude above ground
and are liable to injury from severe frost.
If on account of rainy weather or for any other cause the potatoes can
not be dug before frost or immediately afterwards, the vines should be
cut away and the potatoes removed at the first opportunity. If cold
weather continues it may be necessary to draw a little extra soil over
the hills to protect the potatoes, or the vines may be piled in a ridge
over the row. A very slight frosting of the potatoes will cause them to
decay within a short time after being placed in storage.
It is desirable that the soil should be comparatively dry at the time
of harvesting sweet potatoes, and bright, drying weather is essential
to the proper handling of the crop. Sweet potatoes differ from Irish
potatoes in that they are not so easily injured by sunlight. However,
they should not be exposed for any length of time if the sunshine is
very warm. During the handling in the field it should be the purpose to
remove all soil and surface moisture from the potatoes. Sweet potatoes
should not lie exposed upon the surface of the ground during the night.
_Grading and Packing._--In sorting sweet potatoes preparatory to
packing, about four grades are recognized, as fancy, primes, seconds
and culls. Those packed as fancy include only the most select, both
in size and shape. The primes include all those adapted to general
first-class trade, while the seconds include the smaller and more
irregular stock which goes to a lower priced trade. The culls are not
marketed unless good stock is exceedingly scarce, and as a rule are
used for feeding to hogs. Sweet potatoes are usually shipped in barrels
holding eleven pecks each. Some markets require that the barrels be
faced and headed, while for others the tops are slightly rounded and
covered with burlap. Small lots of extra-fancy sweet potatoes are
sometimes shipped in one-bushel crates having raised tops; also in
patent folding crates. Throughout the process of handling care must be
exercised to see that the sweet potatoes do not become bruised, for
upon this their shipping and keeping qualities greatly depend.
_Storage._--Unlike most perishable products, the sweet potato requires
warmth and a dry atmosphere while in storage. The method of storing
will depend both upon the locality and the quantity of potatoes to be
cared for. The temperature and conditions of a rather cool living room
are admirably adapted for keeping sweet potatoes intended for home use
in the North, while in the South they may be placed in pits or stored
in outdoor cellars. The home supply may be placed in crates and stored
in a loft over the kitchen part of the dwelling. Sweet potatoes should
not be stored in bags or in barrels without ventilation.
The seed stock for planting the following year should be selected and
stored separately in a small bin. As the potatoes are separated into
their respective grades they are put into baskets and carried to the
bins. Some growers prefer to do the grading in the field, but this
necessitates the employment of a larger percentage of expert labor and
delays the work of getting the potatoes hauled to the storehouse. Women
and children can pick up the potatoes in the field, and two or three
experienced men can do the sorting and grading at the house in a much
shorter time and in a more satisfactory manner.
Before starting to fill a bin, 2 or 3 inches of dry pine needles,
straw, or chaff should be placed upon the floor. Beginning at the back
of the bin the potatoes are piled to a depth of 30 or 40 inches until
the entire floor space is covered and a number of slats are required
to be placed across the doorway opening. A few grain bags filled with
straw should be placed upon the potatoes at intervals from front to
back of the bin, and upon these planks on which the men may walk while
carrying in the next layer of potatoes may be laid. In this way a
bin may be filled to a depth of 8 or 9 feet by about three layers.
By dumping them in layers the potatoes have an opportunity to become
thoroughly dry before a new layer is placed over them.
_Temperature and Ventilation of Storage Houses._--Two or three days
before beginning to bring in the potatoes, the storage house should
be thoroughly cleaned and the heating appliance put in working order
and started, in order to have the house both warm and dry when the
crop comes in. Throughout the time of storing and for about ten days
after the potatoes are all in the bins a temperature of 85° or 90° F.
should be maintained in the house, with plenty of ventilation. This
constitutes what is known as the sweating or curing process, and the
keeping qualities of the potatoes depend upon the thoroughness with
which this part of the work is done. Wood-burning stoves are frequently
employed for heating sweet potato storage houses, but a hot-water
boiler with coils of pipes along the walls of the building is very
satisfactory.
After the crop is all in and thoroughly cured, the temperature of the
storage house should be gradually lowered and may vary between 55°
and 65° F., but considerable ventilation should be maintained. Sweet
potatoes should be handled very carefully and as few times as possible,
the essentials to good keeping being a reasonable degree of warmth,
a dry atmosphere, and careful handling. Great care should be taken
with the seed for the next year's planting to see that it is carefully
handled and properly stored. While a temperature of 80° or 85° F. is
required to properly start the seed into growth in the spring, a higher
temperature during a long period of time in storage is liable to injure
or even kill the buds. Potatoes intended for seed should not be stored
in too great quantities, and where but a small supply is needed they
can often be kept buried in dry sand after having first been thoroughly
cured. The sand used for this purpose should be baked to insure the
driving off of moisture, and may be placed around the potatoes while
slightly warm. In controlling the ventilation of the storage house
during the winter months, outside air should be admitted only when
quite dry and when its temperature is lower than that of the air in the
storage house. If warm, moist air is admitted considerable moisture
will be deposited upon the potatoes, thus injuring their keeping
qualities.
_Loss from Shrinkage in Storage._--Under proper storage conditions
sweet potatoes will shrink from 6 to 10 per cent, but the loss in
weight will be greater if the temperature of the house is carried too
high. If the potatoes are not mature when dug from the field the loss
from shrinkage may be as much as 15 per cent, and immature stock should
be marketed early in the winter.
_Marketing During Winter Months._--For marketing from outside pits it
is desirable to have the quantity stored in one pit small enough to
permit of all being removed at one time. The potatoes may be removed
from outdoor cellars as desired. In marketing from heated storage
houses the potatoes should not be disturbed until they are barreled
or crated, and then they should be placed directly upon the market
and sold without delay. When shipping during cold weather the barrels
should at least be lined with paper, and a covering of heavy brown
paper over the outside of the barrels will form a safeguard. If the
potatoes are shipped in carload lots during the winter the cars should
be either of the regular refrigerator type or felt lined.
_Varieties._--Of the large number of varieties of the sweet potato
there are not more than ten that are now of great commercial importance
in the United States. For the markets that require a dry, mealy-fleshed
potato those varieties belonging to the Jersey group are suitable. For
the southern trade and where a moist-fleshed potato is desired those
commonly designated as yams are in demand. Among the Jerseys that are
extensively grown are the Big-Stem Jersey, the Yellow Jersey and the
Red Jersey. The principal varieties of the yam group are the Southern
Queen, the Pumpkin Yam, the Georgia, the Florida, and the Red Bermuda.
Of the varieties mentioned there are a large number of special strains,
known under many local names. In the selection of varieties for home
use one must be governed largely by locality. As a rule those of the
Jersey group will thrive farther north than those of the so-called yam
types. For market purposes the particular variety or strain grown in
the vicinity should first be selected, and afterward other varieties
may be experimented with in a small way.--(F. B. 255, 295, 324;
Tuskegee E. S. 2, 10, 17; Ariz. E. S. 86; N. Mex. E. S. 70; S. Car. E.
S. 5, 136; S. Dak. E. S. 91.)