Title: Sweet potatoes
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Permanent Link: http://ufdc.ufl.edu/UF00026373/00001
 Material Information
Title: Sweet potatoes
Alternate Title: Bulletin 61 ; Florida Agricultural Extension Service
Physical Description: Book
Language: English
Creator: Spencer, A. P.
Publisher: Agricultural Extension Service, University of Florida
Publication Date: April, 1931
Copyright Date: 1931
 Record Information
Bibliographic ID: UF00026373
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aab7774 - LTQF
amt6873 - LTUF
47285975 - OCLC
002570560 - AlephBibNum


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The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

(A Revision of Bulletin 34)

(Acts of May 8 and June 30, 1914)




Fig. 1.-Sweet potatoes piled fcr the round bank.

Bulletins will be sent free upon application to the
Agricultural Extension Service

April, 1931

Bulletin 61



P. K. YONGE, Chairman, Pensacola
W. B. DAVIS, Perry
FRANK J. WIDEMAN, West Palm Beach
J. T. DIAMOND, Secretary, Tallahassee

JOHN J. TIGERT, M.A., LL.D., President of the University
WILMON NEWELL, D.Sc., Director
A. P. SPENCER, M.S., Vice-Director and County Agent Leader
R. M. FULGHUM, B.S.A., Assistant Editor
E. F. STANTON, Supervisor, Egg-Laying Contest
W. T. NETTLES, B.S., District Agent
H. G. CLAYTON, M.S.A., District Agent, Organization and Out-
look Specialist
J. LEE SMITH, District Agent
R. W. BLACKLOCK, A.B., Boys' Club Agent
HAMLIN L. BROWN, B.S., Dairyman
E. F. DEBUSK, B.S., Citrus Pathologist and Entomologist
N. R. MEHRHOF, M. AGR., Poultryman
WALTER J. SHEELY, B.S., Agent in Animal Husbandry'
J. E. TURLINGTON, Ph.D., Agricultural Economist2
FRANK W. BRUMLEY, M.S.A., Agricultural Economist, Farm
W. R. BRIGGS, B.S.A., Assistant Agricultural Economist, Farm
D. E. TIMMONS, M.S.A., Agricultural Economist, Marketing
VIRGINIA P. MOORE, Home Improvement Specialist
LUCY BELLE SETTLE, B.S., District Agent
RUBY MCDAVID, District Agent
MARY E. KEOWN, M.S., District Agent
ISABELLE S. THURSBY, B.S., Food and Marketing Agent
EVA R. CULLEY, B.S., Acting Nutritionist

1In cooperation with U. S. D. A.

The total production of sweet potatoes in the United States
for the year 1930 was estimated at 71,154,000 bushels. The
Florida sweet potato average has for the past ten years been
2,800 to 2,900 acres. There has, however, been a tendency in
recent years to increase the acreage in early plantings. The
yields per acre in Florida over a period of years are about the
same as the average for the United States.
The sweet potato crop of Florida should be one of its major
crops, particularly in the former cotton growing area where the
soil is so well adapted to growing sweet potatoes. Many of the
difficulties that have arisen in storing and shipping sweet po-
tatoes have been overcome. These facts are sufficient to warrant
considerably more emphasis being placed on the growing of
sweet potatoes than has been heretofore.

A sandy loam soil with a clay subsoil is well adapted to the
growing of sweet potatoes. The crop, however, can be grown
under a variety of soil conditions with a fair degree of success.
This is true particularly in Florida, due to this state's light soils
and warm climate.
Of all the types of soil, rolling pine land is usually selected
because of its suitability to the crop and the ease with which
it can be tilled. With sufficient drainage, proper culture, and
a fair amount of organic matter in the soil, a good yield of po-
tatoes may be expected from such soil, if moisture conditions
are held fairly uniform throughout the season.
Sandy flatwoods lands also produce good crops. Where drain-
age is provided and the plants are set on beds, a satisfactory
yield may be expected, if other conditions are favorable. How-
ever, special provision for drainage is essential for most flat-
woods lands.
Rolling hammock lands with compact subsoils are used very
generally for growing sweet potatoes, and, with a fair amount
of humus, a satisfactory crop may be expected from such soil.
But if these hammock lands are not well drained or are too
heavy, they are not as suitable as the pine lands.
A fair amount of organic matter is essential. Without it the
soils dry out during dry periods, and they require much more

Florida Cooperative Extension

fertilizer. Where vegetation can be turned under each year, it
results in the same beneficial effects for sweet potatoes as for
other farm crops.
Muck soils tend to produce a heavy growth of vines and un-
even sizes of tubers, and in some cases no tubers at all. In some
cases tubers become abnormally large and almost worthless for
table use. However, as muck lands become compact and well
drained, particularly if they contain some sand, fairly good crops
may be expected.
Very thin sandy lands usually produce sweet potatoes of a
good quality, but too often the yield is low. Such soil, being
so thin, is lacking in organic matter and, consequently, has not
the power to retain moisture. In most cases it is not profitable
to grow sweet potatoes on such land, unless it is improved by
turning under vegetation and by fertilizing heavily.
Sweet potatoes can be grown successfully on new land, par-
ticularly when planted as a mid-summer crop. They do not pro-
duce best when planted early in the spring. The soil must be
moist and warm to produce a satisfactory yield, otherwise the
potatoes are likely to be long and stringy and unfit for market.


Like any other root crop, the sweet potato requires good culti-
vation as long as it is possible to get between the rows. As the

Fig. 2.-Siding up the beds with a specially constructed implement.
(Courtesy USDA.)

Bulletin 61, Sweet Potatoes

plant is grown on beds in Florida, surface cultivation requires
special implements, especially after the vines begin to run.
It is important that the land be prepared thoroughly far
enough in advance of setting that a good moisture supply may
be insured. Where potatoes are to be planted early in spring,
the land should be plowed early in January, in order that it may
settle and capillary attraction be established between the soil
and the subsoil before the dry months. During dry weather,
if plowed immediately before the plants are set, the soil will
become very dry and many plants will die. It will be difficult
to make those that live grow off rapidly, which is necessary for
good yields. The plowing should be broadcast and from six to
eight inches deep, depending on the soil. If no crop is to precede
the sweet potatoes, it is well to keep the surface of the soil har-
rowed in order to make it firm and moist.
Usually it is not advisable to rebreak the land before planting.
Simply make the beds, apply the fertilizer, and set the plants.
Where early preparation is not provided, the soil is likely to
dry out, which will result in a poor stand, a slow growth of the
vines, and most commonly a low yield of potatoes that are mainly
culls and unfit for market.
A good supply of humus in the soil is important for supplying
plant food, as well as for retaining moisture. Therefore, on
the average pine lands where leguminous crops, grasses, or other
vegetation can be turned under and rotted before planting time,
the soil will be much improved and the plants will get a greater
amount of fertility from the commercial fertilizer applied. In
addition the soil will retain much more moisture, making doubly
sure the prospects for a good yield.


The time of planting will have a decided effect on the yield.
The yields from very early plantings which are harvested early
are usually lighter than those from plantings made just previous
to the season of summer rains. This is principally due to a
warmer soil and a more constant supply of moisture during sum-
mer. When plants are set in early spring, the soils which hold
moisture well should be selected. On the higher sandy soils used
generally for mid-summer plantings, unless irrigation is sup-
plied, early plants are likely to suffer from lack of moisture.
Sweet potatoes require warm soils and the temperature of the

Florida Cooperatice Extension

soil in early spring is usually not quite enough to induce the
most rapid growth.
To have an early summer crop, it is necessary to set plants in
March or early in April; but where a maximum yield is desired
and no special preparations are in mind for marketing early,
it seems best to set the plants in May or June. Slips should be
used for setting up to June 1, after which vines should be used.
The season of planting, however, must be determined to some
extent by the dampness of the soil. It is unwise to set out
plants when the soil is very dry, unless an irrigation system
has been provided, as many of the plants will die and those that
live will grow off slowly, becoming spindling, and produce a
poor yield.
Under favorable conditions planting can continue up to Aug-
ust 1, but usually this is too late for heaviest yields. Plants
set as late as this are likely to make a vigorous growth, while
young, when the soil is very moist, but will yield poorly, if there
should be a lack of rainfall in September or before the plants
have set any potatoes. Had such potatoes been started well in ad-
vance of the rainy season, allowed to establish a good root system
and to make a substantial growth by September, rainfall and
temperature variations would have affected them less.
For the main crop it is seldom advisable to plant before May
15, for, if planted earlier and not harvested until late fall, many
potatoes are likely to be over-sized and cracked, and unfit for
market purposes. Therefore, a good time to set sweet potato
plants for the late crop is between May 15 and July 10. An ex-
ception to this is when the rainy season is prolonged through

Experiments conducted at the Florida Experiment Station and
published in Bulletin 156 of that station show that sweet potatoes
make the heaviest yields on average lands when a complete fer-
tilizer is used. These experiments were conducted for five suc-
cessive years on sandy pine land of average fertility. In each
case where any one of the three essential elements-ammonia,
phosphate, and potash-was omitted, the yield was notably less
than where these elements were applied.
The plots receiving no ammonia produced an average of ap-
proximately 37 bushels to the acre less than the plots receiving

Bulletin 61, Sweet Potatoes

The plots receiving no phosphate produced an average of 52.2
bushels to the acre less than where the phosphate was applied.
The plots receiving no potash produced 121.9 bushels to the
acre less than the plots that received potash.
These experiments, therefore, indicate the advisability of a
complete fertilizer and, in particular, the importance of the
potash element.
Two forms of ammonia were used, sulphate of ammonia and
dried blood. Dried blood gave an increase of 5.6 bushels to the
acre over sulphate of ammonia.
Superphosphate (acid phosphate) was the only form of phos-
phate used.
Two forms of potash, sulphate and muriate of potash, were
used. The plots fertilized with muriate of potash yielded an
average of 18.2 bushels to the acre more than the plots fer-
tilized with sulphate of potash, thus showing the superiority of
Plots that received an application of 2,000 pounds of ground
limestone to the acre produced approximately the same yields
as where no lime was used. This indicates that lime is of little
or no value for sweet potatoes on the average Florida land.
Fertilizer Application.-To produce maximum yields on aver-
age pine land, apply from 600 to 1000 pounds of fertilizer per
acre for the late crop and from 1,500 to 2,000 pounds to the
acre for the early crop. The actual amount needed is determined
by soil conditions.
On light, poor soil it is seldom profitable to apply more than
600 pounds of fertilizer to the acre. A larger amount may in-
crease the yield, but not sufficiently to pay for the extra expense.
Conditions determining the amount of fertilizer that can be
used profitably depend on the kind of soil, its natural fertility,
the character of its subsoil, the humus it contains, and its gen-
eral physical condition. Usually where the soil is in a high
state of cultivation and has more than the average natural fer-
tility, large amounts of fertilizer may be used profitably. But
where the soil is loose and open, lacks humus and fertility, and
is apt to be affected by unusual rains or continued drought,
large amounts of fertilizer are seldom profitable. No definite
amounts or formulas can be recommended for giving best results.
However, the above suggestions can be used as a guide.
Where the soil contains large amounts of humus and organic
matter, as does muck soil, the amount of ammonia may be re-

Florida Cooperative Extension

duced to one-half or one-third, but the phosphate and potash
should be decreased very little if any. These soils are unusually
rich in ammonia but do not have an excess of either phosphate or
Analysis.-A sweet potato fertilizer analysis should show ap-
proximately the following: 4 percent ammonia, 6 percent phos-
phoric acid, and 6 percent potash. This formula may be pur-
chased in mixed goods or made from the following materials:
Sulphate of ammonia ................. 25 percent 320 pounds
Superphosphate ............................. 16 percent 750 pounds
Muriate or sulphate of potash .... 48 percent 252 pounds
Inert matter (filler) ..................... 678 pounds
Total 2,000 pounds (1 ton)
If the goods are home-mixed, there is no occasion to add the
filler material.
In case it is desired to apply a fertilizer with analysis 4-6-6
from the above materials equivalent to 100 pounds to the acre,
mix together the following materials:
Sulphate of ammonia ................ 25 percent 16 pounds
Acid phosphate .............................. 16 percent 38 pounds
Muriate or sulphate of potash .... 48 percent 13 pounds
Total 67 pounds
This gives a total application of 67 pounds to the acre, but
it is equivalent to 100 pounds to the acre of 4-6-6 fertilizer. The
amount of each material needed for making up any given amount
can be calculated from these figures. To illustrate-if you wish
to apply 900 pounds to the acre, multiply by 9 the amount stated
for 100 pounds. Do this for each of the materials used.
When to Fertilize.-If the fertilizer is applied early in spring,
one application two weeks before the plants are set is recom-
mended. If, however, the fertilizer is applied for summer plant-
ing the amount used should be divided into two applications.
The first application should be made two weeks before the plants
are set, and the second after the plants have been set one month.
Stable Manure, if available, can be used to advantage at the
rate of two to five tons to the acre. Apply manure and fertilizer
to the soil in about the following manner: After the ground has
been prepared and is ready for planting, open up furrows four
feet apart and distribute the manure into them. Then cover this
manure with two furrows, one on either side. This forms a
shallow bed. Apply commercial fertilizer on these half-made
beds and work it into the soil by running a one-horse fertilizer

Bulletin 61, Sweet Potatoes

distributer over the top of the beds. Allow the beds to remain
in this condition for about two weeks, until about ready to plant.
Then finish preparing the beds by plowing furrows on either side,
making the beds as high as necessary. Set the plants in these

Fig. 3.-On fertile soils, well-fertilized, sweet potatoes grow luxuriantly
in Florida.
Where no stable manure is used the opening of this furrow
is unnecessary. Plow up the shallow beds and proceed with
the commercial fertilizer, the first application of which should
be in the ground two weeks before the plants are set, lest it
injure the newly set plants. The second application should be
made about thirty days after the plants are set. This will
make it necessary to apply it in the sides of the beds. Work
it in with a cultivator. This will tend to pull down the beds,
but they can be thrown up later with a plow.
Sweet Potatoes on "Cowpenned" Land.-The penning of cattle
on land to be planted to sweet potatoes usually gives good results
because of the manure and tramping the land gets. It, at least,
emphasizes the importance of using manure for sweet potatoes.
Vegetation in the Soil.-The importance of adding vegetable
matter to the average sweet potato soil of Florida cannot be over-
estimated. All vegetation should be plowed under soon enough
to decay well by planting time. A leguminous crop is partic-
ularly beneficial for sweet potatoes where it can be turned under
in time to decay before the crop is planted.

Florida Cooperative Extension

Results from the use of added fertilizing matter are best when
the soil has a good supply of organic matter. Because it im-
proves moisture conditions in the soil during the life of the crop,
it is advisable to incorporate into the soil as much of such mate-
rial as is possible.

Fig. 4.-A plant bed properly laid off and boarded up, and of convenient


As sweet potatoes are propagated from plants, provision must
be made for growing an ample supply of plants. In Florida they
can usually be grown early enough, when set in the open. How-
ever, if it is desired to set plants in the field on or before April 1,
the plant beds will need some protection and artificial heat, es-
pecially in Middle, North and West Florida. In South Florida,
if covered with pine straw or some similar material, they will
be protected against freezing.
For a plant bed one should select a protected spot, preferably
on the south side of a windbreak, where the plants will get all
the sunlight possible. The sweet potato does best in a warm
soil with a relatively high temperature. The location should be
well drained and the soil should be fairly fertile.
A plant bed may be either in a shallow excavation or on a

~a~ I


Bulletin 61, Sweet Potatoes

level; in either case the bed should be about five feet wide and
of the necessary length. The bed should not be so wide that it
is inconvenient to pull the plants without stepping on the beds.
Inclose in a frame made of eight-inch boards, as shown in Fig. 4.
In the bottom of the bed should be placed from four to six
inches of fresh horse stable manure. On top of the manure
place a layer of soil three inches thick. Then spread the seed
potatoes over this layer of soil. On the potatoes place one to
one and a half inches of sand or loam soil. If potatoes are cover-
ed too deeply, they will be slow to sprout, as a deep layer of soil

Fig. 5.-Healthy, strong, vigorous plants make the best potatoes.
(Courtesy USDA.)

tends to keep the soil cool and retards sprouting. When the
plants begin showing through the ground, add an additional
layer of soil. To insure long stocky shoots, there should be six
inches of soil over the potatoes at pulling time. After the po-
tatoes are planted the soil must be kept moist by sprinkling.
However, too much water is detrimental, as the temperature of
the bed will be kept down. Add just enough moisture to pro-
mote growth. The bed needs comparatively little attention un-
til the draws are big enough to transplant.
A slip five inches long is ready to be transplanted. After each
crop of draws is pulled, keep the soil moist and in 10 days or
two weeks another crop will be ready to take off.

Florida Cooperative Extension

In estimating the amount of seed potatoes necessary to grow
draws for a given acreage, it is estimated that one bushel will
produce 800 to 1,000 plants for the early crop. Twelve bushels
should be planted for each acre of early planting. If, however,
the seedbed is planted early and the slips are allowed to grow
into vines, three bushels will produce enough vines to set an
acre, if conditions are favorable. When this is done, the slips
should be transplanted to where they will have ample room to
grow and make vines.
A slight application of commercial fertilizer analyzing 4 to
5 percent ammonia should be broadcast on the plant bed about
the time the sprouts are appearing above the soil. Work into
the soil by means of a light rake or hoe. This added plant food
will stimulate and hasten the growth of the plants.
It is also advisable to provide thin canvas or cheesecloth for
the protection of the beds. This material can be stretched over
the bed at night and removed during the day. It prevents ra-
diation of heat from the bed, and thus keeps it warm. Plants
require a temperature of 700 to 800F. to grow well. There will
be little difficulty in holding it above 500F., if the foregoing pre-
cautions are taken.
Where the plants are needed for late planting only, forcing

Fig. 6.-Draws, or slips, crated for shipment. (Courtesy USDA.)

Bulletin 61, Sweet Potatoes

methods will not be necessary, as late plantings will produce all
the plants needed.

Nothing is gained by transplanting potato draws before they
are sufficiently strong, since to do so checks their growth. When
the plants are pulled from the bed, it is best to set them out im-
mediately. However, if they are to be shipped, allow them to
wilt in the shade for at least six hours before packing. This
tends to harden them and to reduce the number dying. Immedi-
ately following a rain is a good time to set out potatoes. If the
area to be planted is small, the plants can be transplanted at
almost any time and watered.
Number of Slips to Plant an Acre.-It requires about 8,000
slips to plant an acre of potatoes with four-foot rows, when
the plants are set 15 inches apart in the row. The width and
distance for planting depend on the richness of the soil and the
variety of the potatoes. 'In soil that is rich the plants can be
set closer than in poor soil; _
and with varieties that pro-
duce many vines the rows
should be a little wider than
with varieties that produce
but few light vines. The
rows should be wide enough
to permit cultivation for five
or six weeks after the plants __.
are set, particularly if set in
early spring when the h
weather is likely to be dry.
If planted in mid-summer ,
when rains are frequent, cul-
tivation to conserve moist- '
ure is not necessary.
Slips Compared with Vines. .
-There is no difference in "
setting the vines and in set- L
ting the slips. However, as Fig. 7.-Proper root development and
the vines usually are set top for transplanting. (Courtesy
later in the season and are USDA.)
larger and stronger, they can be set under less favorable con-
ditions than can slips. This is largely due to the superior strength

Florida Cooperative Extension

of the vine and its ability to withstand unfavorable conditions.
In setting the vines, first cut them into 15-inch lengths, insert
the butt end at least 6 to 8 inches deep. The soil should be left
firm around the vine in order to prevent the bed from drying
Vines are preferred to slips, where it is practical to grow them,
since the vines are usually stronger and mature their crop quick-
er than do slips. This is due to the vigor of the vine cuttings.
It is further true that many more vine cuttings than slips can
be secured from a bushel of seed. For early planting one must
depend on slips, but for late planting it will not be difficult to
secure ample vine cuttings from a much smaller amount of seed,
especially if the slips are transplanted into rows for the purpose
of growing vines.
There are four or five com-
mercial varieties of sweet
potatoes recommended f o r
Florida. Several others are
grown locally but do not seem
to have any particular merit
and, consequently, have
little commercial importance.
The most important com-
mercial varieties are Porto
Rico, Improved Porto Rico,
Triumph, Nancy Hall, and
Big Stem Jersey. The Red

Fig. 8.-The Porto Rico, famous in the South for its richness of flavor and
rare delicacy.

Bulletin 61, Sweet Potatoes

Providence and Norton Yam are grown commercially but are
of less importance. Other varieties such as Dooley Yam, Pump-
kin Yam, Nigger Killer, "Pattysaw" and Red Buck, are grown in
gardens but are not recommended for commercial plantings.
The Porto Rico is the most popular variety throughout Flor-
ida on account of its rich color, moist soft flesh, and its rich,
sweet and juicy flavor. It is also very popular in the markets
of other southern states, and, in fact, wherever a moist-fleshed
potato is demanded. It yields on the average a good crop of
marketable potatoes, which can be stored several months and
kept in good condition, if harvested without being bruised.
It produces heavy, purple vines, the leaves being large and
thick and greenish brown in color with purple markings on the
veins, around the edge of the
leaf and on the petiole stems.
The Improved Porto Rico
is a strain of the Porto Rico
variety having a deeper col-
or than the standard Porto
Rico. This variety has come
into much favor in recent
years and is now extensively
The Nancy Hall is less
popular for home use and
for most Southern markets
than is the Porto Rico. The
potato is light yellow in color
with flesh of a creamy-pink-
yellow. When cooked, the

Fig. 9.-The Nancy Hall cooks soft, moist and sweet and is popular on
the Northern markets.

Florida Cooperative Extension

flesh is moist, soft and sweet, but not as rich in appearance as
the Porto Rico.
It is an average yielder on light soils and has proven a satis-
factory variety to grow under average conditions. Of moist
potatoes it is one of the most satisfactory for northern markets.
It has the disadvantage of a tendency to crack, if grown on
rich soil or if allowed to remain in the soil for some time after
maturing. The vines are inclined to be bushy. The leaves are
mottled greenish yellow with purple markings at the junction
of the blade and stem.
The Triumph is recommended for early planting, particularly
when the crop is to be shipped to northern markets. It is drier
than the Porto Rico or Nancy Hall and for that reason is less
liable to bruising and is a better shipper.
When propagated from slips, there is little difficulty in pro-
ducing early potatoes of this variety. And for spring ship-
ments to northern markets it is one of the most dependable.
Since it is a comparatively
dry potato, it is not very
popular o n southern mar-
kets. However, where the
Quality is good it is com-
paratively free from stringi-
ness and when ripe is fairly
'. sweet. The vines make a
heavy growth and the leaves
are deep green with purple
stems and veins. Both the
peel and the flesh of the roots
are light yellow in color.

Fig. 10.-The Triumph is a good shipper.

Bulletin 61, Sweet Potatoes

The Big Stem Jersey is a dry mealy potato and sells much
better on northern than on southern markets. It has not been
popular in the South because of its dryness. In the North it is
well known as being dry and mealy. It can be handled easily
without bruising.
When this potato is planted in Florida it is usually with an idea
of shipping to the early northern markets. It can be produced
and placed on those markets in July, or earlier than most other
varieties. This requires very early planting. When grown early
in spring, particularly if the soil is dry, the yield is often light.
For that reason it has not
been grown to any extent
except by those who have
made special preparation to
grow it at this season. It
is doubtful if it ever will be
a satisfactory variety for
home or local consumption.
The vines are rather
scant, long a n d creeping,
and the leaves are small and
green in color. The roots
are dark yellow and their
flesh creamy yellow in color.
When cooked it is dry and

Fig. 11.--The Big Stem Jersey, a good shipper and popular in the North
because of its dryness and mealiness.

The Norton Yam is a good variety for local markets and for
home consumption. It is a sweet, moist potato but is inclined
to be stringy, if its growth is retarded by dry weather. The
roots are russet yellow in color, and their flesh white, flaked

Florida Cooperative Extension

with yellow. The leaves and stems are rich green and the vines
light green in color. The vines are inclined to have a long strag-
gling growth.
The Red Providence is grown commercially and for home use.
It is usually a good yielder and is propagated easily. In color
the roots are tan, shading into yellow. The flesh has a tinge of
pink. The potato is comparatively free from stringiness. It is
moist and a good keeper, if harvested without bruising. The
vines are green with purple markings at the nodes, and the leaves
have purple stems which shade into green. The vines make a
Medium heavy growth.
The Pumpkin Yam is suit-
ed for local consumption. It
is a very juicy potato and
bruises easily, unless handled
carefully. As to color, the
roots are salmon with a rich
yellow flesh. When cooked
it is sweet and juicy. The
leaves are long and irregu-
lar, with prominent yellow
The Nigger Killer, "Pat-
tysaw", and Red Buck are of
little importance from any
standpoint. They seem able
to produce light inferior
crops under neglected con-

Fig. 12.-The Norton Yam is good
for home use and to supply lo-
cal markets. It is a sweet, moist
potato. However, it does not do
well when the weather is dry.

Bulletin 61, Sweet Potatoes

editions. They are moist and comparatively sweet, but are not
recommended for commercial plantings.


The practice of selecting seed has been neglected very greatly
in much of the sweet potato growing area. Little along this line
has been done in Florida, with the result that the average yield
is low. In fact it is difficult
to secure a high yield of uni-
form, marketable potatoes.
While the lack of good seed
is not altogether responsible
for this condition, it is an
important factor.
The planting of sweet po-
tato vines from volunteer
plants is partly responsible
for many low yields. These
volunteer vines come up
from potatoes which were
overlooked when the previ-

Fig. 13.-The Red Providence is grown to some extent for commercial and
home use.

ious year's crop was harvested. Usually such potatoes are small
and inferior. One cannot expect plants from such seed to give
the best returns, nor to produce roots uniform in color and shape
and true to variety.
The practice of bedding the inferior or cull potatoes for seed
is also responsible for low yields. While there are many small
roots suitable for seed, the probability of getting low-yielding
plants from them is so great that it is better to feed them to

Florida Cooperative Extension

livestock and to purchase seed, if necessary, even at a much
greater expense.
Sweet potato seed should be selected for uniformity of type,
color and variety, and should be free from disease. Careful seed
selection year after year results in the ultimate production of
a higher percentage of marketable potatoes. Such potatoes can
be graded and packed so as to compare favorably with the best
that reach the eastern markets, and also make a decided im-
provement in the general appearance of the potatoes on southern
There are several diseases of sweet potatoes that mar their
appearance and increase the number of seconds and culls. By
the proper selection of seed when the potatoes are dug, the
proper storing of seed potatoes, the careful re-sorting, the throw-
ing out of all diseased tubers, and the disinfecting of seed, the
amount of diseased potatoes will be reduced, their yield in-
creased, and their quality improved.


Since many diseases are carried into the field by planting dis-
eased seed, it is advisable to treat all seed immediately before
bedding. This is done by placing the potatoes in a solution made
of 1 ounce of corrosive sublimate crystals mercuricc chloride)
dissolved in 8 gallons of water. Use a wooden container, let
potatoes remain in the solution for 10 minutes, then spread them
out to dry without being rinsed. Then bed immediately. In case
the soil is generally infested, this treatment is of little service.
In such a case, plant some other crop.
Bulletin 212 of the Florida Experiment Station, Diseases of
Sweet Potatoes in Florida, contains further information on dis-
eases and seed treatment.


Much care is needed when harvesting sweet potatoes to avoid
bruises. Southern potatoes, because of their high content of
water, are bruised more easily than the drier varieties. The
diseases of sweet potatoes can do comparatively little damage,
unless the potatoes are bruised or broken. If the crop is to be
stored for several months, too much care cannot be exercised
to prevent bruising. If comparatively free of diseases and if
carefully handled to prevent bruises, breaks, and cuts, practically

Bulletin 61, Sweet Potatoes

all potatoes will cure well and few will rot. However, if they
are hauled loose in the ordinary
wagon body, handled careless-
ly from the wagon to the cur-
ing house by forks or shovels,
the blemished and rotted will
amount to as high as 75 per-
cent or more of the original -
A turning plow with two
rolling colters attached to the
beam in such manner that they
will cut the vines is a satisfac-
tory implement for getting
sweet potatoes out of the
ground. Sweet potatoes should
be picked up carefully before
being exposed to the sun for
of time They Fig. 14.-The hamper is suitable
any length of time. The y for use where sweet potatoes are
should not be thrown into piles being shipped in carloads; it is
easily loaded into the car. (Cour-
as this is sure to bruise them. tesy USDA.)


Sweet potatoes are packed in hampers, baskets, crates, and
barrels. The kind of package used is determined largely by
how the potatoes are shipped. For car-lot shipments the hamper
has the advantage of being packed easily in the car. For ex-
press shipments this package is objectionable in that it is more
easily broken than the bushel basket or crate.

Fig. 15.-Baskets are convenient containers. (Courtesy USDA.)

If sweet potatoes are placed in storage houses, the bushel crate
is preferred, since crates of this type may be filled with pota-

Florida Cooperative Extension

toes immediately from the field and stacked up in such a way as
to provide ventilation. This last crate, therefore, minimizes
handling and bruising. If the potatoes are carefully sorted in
the field, they can be placed in these crates immediately; but
usually they must be re-sorted just before being shipped in or-

Fig. 16.-Crates minimize handling and brusing. (Courtesy USDA.)

der to remove the blemished or unmarketable. The tight bar-
rel is used generally when shipping direct from the fields to the
market. This barrel is not headed as is the Irish potato barrel,

Fig. 17.-Barrels are generally used when shipping direct from field to
market. (Courtesy USDA.)

Bulletin 61, Sweet Potatoes

the potatoes being held in by a covering of burlap fastened down
with a hoop. Such a package would not be suitable for storing
in a storage house because good ventilation cannot be secured.
Packages filled and ready for marketing should contain pota-
toes uniform in color, size, and quality. The packages should
be well filled so that they will be held firm in the pack and thus
prevented from settling down and being bruised in transit.
Never ship sweet potatoes in sacks for long distances. This
is impossible to do without practically every potato becoming
bruised. As with any other product, potatoes in a neat-appear-
ing package usually find a ready sale at a good price, and, there-
fore, care must be exercised in placing sweet potatoes on the
market that they may sell for the best price.


Sweet potatoes to be stored in houses or banks for two or
more months must be comparatively free of bruises and blem-
ishes and well-matured, or many will decay and others grade
low. Before being piled together, broken and bruised ones
should be sorted out for immediate use.
Rotting in storage is caused by a fungus that develops slowly
when the potatoes are spread out thin and have a free cir-
culation of air over them. When they are piled together and
have but a limited circulation of air, there is usually some in-
crease in temperature and moisture in the air about them, which
makes conditions favorable for the action of the fungus. This
accounts for the fact that potatoes stored in small banks keep
better than those scored in large banks.
The round bank, as shown in Fig. 1, has an advantage over
the larger bank in that the pile is small and there are more po-
tatoes exposed to a free circulation of air. If the bank contains
15 bushels or less, it will hardly be necessary to place a venti-
lator in the center of it. However, the top should have a venti-
lator so that, if there is any heating, the warm air can escape.
After the potatoes are shaped up they should be covered with
about four inches of straw, and over this a thin layer of dirt in
order to keep out cold and rain.
When a larger quantity of potatoes is to be stored, the bank
can be long and narrow. But on account of the larger pile there
will be more heating, consequently more ventilation will be
needed. The ventilated bank, as shown in Fig. 18, provides a
free circulation of air from one end to the other.

Florida Cooperative Extension

Fig. 18.-A ventilated sweet potato bank, designed and used by T. K.
Godbey, Waldo, Florida.
Invert a V-shaped trough and lay it in the bottom of the bed.
Under this place supports to hold the trough two inches off the
ground. Pile the potatoes over this ventilator.
Such a bank can be made five or six feet wide at the bottom
and about four feet high and can have any desired length up to
20 feet. Such a bed 20 feet long will hold about 200 bushels.
When the beds are shaped up and ready to be closed in they
should have a light layer of straw, held down and protected by
a layer of boards, the upper ends of which rest on a ridge pole.
The boards should overlap sufficiently to keep out rain. No
straw should be placed in the bottom of the bed. The potatoes
will keep better if laid on the ground.
A layer of dirt can be placed over the boards. This will be
needed during frosty weather. The potatoes will keep much
better, if a fairly uniform temperature is maintained both day
and night. To provide such a temperature, a thicker wall than
provided by the boards and straw will be necessary. In unus-
ually cold weather both ends of the ventilator in the bottom of
the bed can be covered with dirt.
Ample ventilation is necessary to keep sweet potatoes sound
and fresh after being stored. If fresh air can enter from the
bottom, circulate through the potatoes and escape at the top of
the bank, the potatoes will keep with comparatively little shrink-
ing or rotting. And if a uniformly cool temperature is main-
tained, there will be little sprouting.

Sweet Potato Curing Houses are in general use in many sweet
potato sections. Where a large acreage is grown for several

Bulletin 61, Sweet Potatoes

years in succession, a curing house is recommended. Such a
house is not recommended unless there are 1,500 bushels or more
to be stored. In small houses it is not easy for the temperature
to be held uniform. When the outside temperature is frequently
70F., or higher, it is often difficult to prevent sprouting. This
can be controlled in a large house better than in a small one.
Also, for a crop of 1,500 bushels or less, the initial cost and neces-
sary supervision will be too large to justify a storage house.
Therefore, if the crop is small, it is more profitable either to
market the potatoes at harvesting time or to store them in a
A storage house with a capacity of from 5,000 to 10,000
bushels can be operated at a relatively low cost. A small house
requires practically the same supervision that a large one does.
In either case an attendant must watch and hold the tempera-
ture and moisture in the house at their proper places.
Digging and Handling.-Potatoes to be cured in a storage
house should be left in the ground until well matured. If frost
destroys the vines, the potatoes should be dug at once or have
their vines cut off at the level of the ground. If the dead, rotting
vines remain attached, germs of decay will enter the potatoes
and they will decay in storage. After the potatoes are dug they
should be placed in the storage house just as soon as they are
dry. If the weather is clear and relatively cool, allow to dry
before storing; but, if the weather is hot, do not let them remain
exposed to the sun, since to do so will cause them to sunburn.
It is usually best to house the potatoes as they are dug, allow-
ing them to remain on the ground just long enough to dry.
In digging potatoes care should be taken not to bruise them
by throwing from one row to another or into a loose wagon bed
or into bags. Sort and put into a basket or box, load onto the
wagon and haul them directly to the storage house. If stored
in crates, there is no occasion to handle more than once. If the
grading is done in the field and the different grades are kept
separate, handling at the cars will be facilitated.
Houses can be built with or without bins. Those without bins
require that the potatoes be stored in crates. This is economical
and usually most practical, as it saves handling the potatoes
after they reach the storage house, and the boxes can be piled
up in such a way that air can circulate freely through them.
Curing the Potatoes.-As soon as the potatoes are stored ex-
cess moisture in the house should be driven off by means of a

Florida Cooperative Extension

stove or heating flue. For the first ten days the temperature
in the house should be from 80 to 850F. with ample ventila-
tion. The temperature maintained will depend on weather con-
ditions. Ventilation is needed to drive off the excess moisture
and to keep the potatoes fairly dry. During the day the win-
dows and doors may be opened but at night they should be
After 10 days the temperature within the curing house should
be gradually reduced to 550, where it is kept as near as pos-
sible as long as the potatoes are in the house. In case the tem-
perature falls to 450 or lower, a fire should be started again and
the temperature raised to 550. If the house becomes moist at
any time during the curing period, it will be necessary to dry
it out.
A storage house can be heated with an ordinary sheet-iron
stove. The more uniform the temperature can be held the bet-
ter the potatoes will keep. For this reason coal is preferred to
wood for heating purposes. In commercial storage houses with
a capacity of 10,000 bushels or more, a large heating system is
advisable. The important points in the control of heat in a
storage house are to bring in fresh air, to drive out all moisture-
laden or foul air, and to keep the temperature within the house

K6 ~.

aj~ 0 a' 4

Y 0

Fig. 19.-Crated sweet potatoes on the way to market. (Courtesy USDA.)

Bulletin 61, Sweet Potatoes

to 55-. In Florida it is difficult to hold the temperature down
to 550, particularly in the fall months when the outside tem-
perature is from 70 to 800. It is important, therefore, in the
construction of the house to be sure that ventilators are placed
properly and that air spaces are in the walls so that a uniform
temperature may be maintained and not constantly varied.
Advantages of the Sweet Potato Storage House are as follows:
First, the sweet potatoes can be kept in a marketable condi-
tion until prices are satisfactory, even for several months after
Second, the potatoes can be placed on the market in good con-
dition with a minimum loss from decay.
Third, sweet potatoes that are stored properly can be shipped
to distant markets several months after being harvested.
Fourth, the grower is enabled to watch his potatoes while
they are in storage, and should they show a tendency to rot or
sprout, he may be able to dispose of them.
Sweet potato storage houses have not been generally used in
Florida largely due to the limited acreage usually grown by
farmers. Before the expense of erecting a storage house is
justifiable, there should be from one to two thousand bushels
of marketable potatoes to be stored, and with a probability of
continued use of the house for three or more years, due to the
building cost and maintenance. Growers also report difficulty
in preventing the sprouting of potatoes due to relatively warm
However, anyone planning to grow or store sweet potatoes
through several years on a relatively large scale could hold
the potatoes from three to six months in such a storage house
and thereby avoid selling them when the markets are over-
The details for the construction of a sweet potato storage
house are contained in Farmers' Bulletin 970, United States
Department of Agriculture, Washington, D. C.


Sweet potatoes may be grown as an early market crop in
Florida if conditions are made favorable for having the crop
ready to harvest in June or July. The demand for this crop
is larger in the northern markets, although there is a limited
demand in the southern markets.
The variety most general recommended for the early crop is

Florida Cooperative Extension

the Big Stem Jersey. The Porto Rico is also grown but as it
does not represent the type of potatoes usually found in the
early markets of the North, the sale of the product is more
restricted. The Big Stem Jersey, being dryer and more accept-
able to trade, usually brings a satisfactory price, especially when
it can be marketed in July or earlier.
In tests made to compare Big Stem Jersey and Porto Rico
sweet potatoes and covering three or more years at the Coastal
Plain Experiment Station, Tifton, Ga., (Bulletin 12), it was
found that the Porto Rico variety consistently gave a higher
yield per acre of total, also marketable potatoes. Where planted
for the early market, the largest yield with both varieties was
obtained when the potatoes were planted on high beds.
In order to produce the early crop, special preparations must
be made. In the first place there must be a good supply of
plants available that are ready to set out early in March. As
a rule there is no difficulty in getting an ample supply of plants
to set out a crop in June but the growth of plants is usually slow
during the early spring months and this has been one of the
great drawbacks in getting an early crop started.
For the early crop,.the plant beds should be planted on or
before January 10 and every care should be exercised to pro-
mote early growth. A statement covering the making of the
bed is carried elsewhere in this bulletin and applies to the early
as well as to the later crop. Care must be taken that the beds
are kept warm by covering them when the temperature is be-
low the average. There must also be a good, moist condition
to induce rapid growing. At the same time the plants must
be grown in the open, otherwise they will be spindling and weak.
Under very favorable weather conditions, plants may be avail-
able from well prepared beds by the latter part of February but
unless conditions for growing are made favorable, the plants
may not be large until late in March. Even this may not be
too late for planting the early crop if the soil and weather con-
ditions are favorable for planting. The methods of growing the
early crop do not differ from those used with the later crop ex-
cept that it may profit to use more fertilizer. Emphasis is placed
on having early-grown, strong, sturdy plants in liberal quantities
so that the early planting will not be delayed.
In the planting of Big Stem Jerseys, preference is given to
seed that has been grown in the Eastern states. Seed grown in
Virginia has given a better stand of plants than Florida-grown

Bulletin 61, Sweet Potatoes

seed. Although this supply of seed may be relatively expensive,
one cannot afford to take chances on getting a poor stand by
planting seed that is uncertain:
When a good yield of potatoes can be harvested on or before
the 20th of July, one may reasonably expect to receive from
$6 to $10 per barrel.
The early spring crop usually produces a lower yield than the
late summer crop but with the higher price per barrel, the crop
is usually profitable if 75 bushels of No. 1 potatoes per acre can
be produced.
The early crop must be shipped in standard barrels and com-
petes with early sweet potatoes from other sections that supply
the Eastern markets.

In order to market sweet potatoes to best advantage, they
must be properly graded and packed. The general practice of
shipping all the potatoes from a field in loose cars, unsorted, is
wasteful. The seller usually gets only the price of his lowest
grade, the best potatoes being sold for the price of the poorest.
It is always best not to ship cull potatoes. They have little
or no market value, at least not sufficient to cover the added
freight charges. Such potatoes have a value from 30 cents to
50 cents a bushel for stock feed or for canning.


Following are the recognized grades of sweet potatoes in the
United States:
U. S. Grade No. 1

U. S. Grade No. 1 shall consist of sound sweet potatoes of
similar varietal characteristics which are practically free
from dirt or other foreign matter, frost injury, decay,
bruises, cuts, scars, cracks, and damage caused by heat,
disease, insects (including weevils), or mechanical or other
The diameter of each sweet potato shall not be less than
one and three-quarters inches nor more than three and one-
half inches, and the length shall not be less than four inches
nor more than ten inches, but the length may be less than
four inches if the diameter is two and one-quarter inches
or more.
In order to allow for variations incident to commercial
grading and handling, five percent, by weight, of any lot

Florida Cooperative Extension

may not meet the requirements as to diameter and length,
and, in addition, six percent, by weight, may be below the
remaining requirements of the grade.
Any lot in which the diameter is not less than one and
one-half inches and which contains a greater percentage by
weight of sweet potatoes below one and three-quarters
inches than is permitted in U. S. Grade No. 1, but which
otherwise meets the requirements of such grade shall be
designated as U. S. Grade No. 1 Medium.
Any lot in which the length is not less than six inches nor
more than twelve inches and which contains a greater per-
centage by weight of sweet potatoes above ten inches in
length than is permitted in U. S. Grade No. 1, but which
otherwise meets the requirements of such grade shall be
designated as U. S. Grade No. 1 Long.
U. S. Grade No. 2
U. S. Grade No. 2 shall consist of sound sweet potatoes
of similar varietal characteristics, not meeting the require-
ments of the foregoing grades, which are free from serious
damage caused by dirt or other foreign matter, frost in-
jury, decay, bruises, cuts, scars, cracks, heat, disease, in-
sects, or mechanical or other means, and which are not less
than one and one-half inches nor more than three and one-
half inches in diameter.
In order to allow for variations incident to commercial
grading and handling, five percent by weight of any lot
may not meet the requirements as to diameter, and, in ad-
dition, six percent by weight may be below the remaining
requirements of this grade.
U. S. Jumbo Grade
U. S. Jumbo Grade shall consist of sound sweet potatoes
of similar varietal characteristics, which are free from
serious damage caused by dirt or other foreign matter,
frost injury, decay, bruises, cuts, scars, cracks, heat, dis-
ease, insects, or mechanical or other means, and which are
not less than three and one half inches in diameter.
In order to allow for variations incident to commercial
grading and handling, five percent by weight of any lot
may be less than the diameter prescribed, and, in addition,
six percent by weight may be below the remaining require-
ments of this grade.
U. S. Grade No. 3
U. S. Grade No. 3 shall consist of sweet potatoes not
meeting the requirements of any of the foregoing grades.

Bulletin 61, Sweet Potatoes

Definition of Grade Terms as Used in These Grades
"Practically free" means that the appearance shall not
be injured to any extent readily apparent upon casual ex-
amination of the lot, and that any damage from the causes
mentioned can be removed without appreciable increase in
waste over that which would occur if the sweet potatoes
were perfect.
"Diameter" means the greatest dimension at right angles
to any portion of a central line running through the sweet
potato from stem end to root end.
"Free from serious damage" means that any damage
from the causes mentioned can be removed without increase
in waste of more than ten percent by weight over that
which would occur if the sweet potatoes were perfect.


Sweet Potato Silage.-The value of the sweet potato as a sil-
age crop has been determined by the Florida Experiment Sta-
tion and reported in Press Bulletin 274 of that station.
In these experiments potatoes were stored in the silo just
as is corn or sorghum. Or, in other words, the potatoes were
run through an ensilage cutter at harvesting time and kept in a
concrete silo until the following May. Sweet potato silage, com-
pared with corn silage, shows the following analysis:
Moisture Crude protein Nitrogen free ext. Fat
Sweet potato silage ........ 54.8 1.82 39.4 0.66
Corn silage .................... 72.7 2.1 15.4 .08
During those experiments a test was made with 10 cows to
compare the feeding values of sweet potato and sorghum silages
for milk production. Both were fed with a concentrated ration
of wheat bran and cottonseed meal. The test was continued for
43 days with the following results:
The cows fed with sweet potato silage produced 2,641 pounds,
or 307 gallons of milk. During the same period the cows fed
sorghum silage produced 2,416 pounds, or 281 gallons of milk.
This gave a difference of 26 gallons in favor of the sweet potato
The cows in this test were as nearly average cows in every
respect as can be selected from the ordinary herd. The test
serves to indicate that the advisability of making sweet potatoes
into silage can be determined only by their market value.
Sweet Potatoes for Milk Production.-In feeding tests con-
ducted by the Florida Experiment Station for the purpose of

Florida Cooperative Extension

comparing sorghum silage and sweet potato silage for milk pro-
duction, it was found that, when fed with cottonseed meal and
wheat bran, 4,8191/ pounds of sweet potatoes produced 3,1221/4
pounds of milk at a feed cost of 17 cents a gallon, and that 6,898
pounds of sorghum silage, with the same additional feeds, pro-
duced 2,8001/4 pounds of milk at a cost of 14 cents a gallon. In
making these tests the amount of silage fed was based on the
digestible nutrients in the foods given, so that practically the
same amount of food value was contained in the sweet potatoes
as in the sorghum silage. It was also estimated that the cost
of the sweet potatoes was 30 cents a bushel and that of the sor-
ghum silage $3 a ton.
For feeding dairy cows the value of sorghum silage may be
estimated at $6 a ton, and sweet potatoes at 60 cents a bushel,
when made into silage. This will give a fair idea of the relative
value of sweet potatoes compared with sorghum silage.
Sweet Potatoes as Hog Feed.-The advisability of feeding
sweet potatoes to hogs is determined also by the market value
of the sweet potatoes. When sweet potatoes are worth more
than 60 cents a bushel, it is seldom profitable to feed them to
hogs. There is, however, in every crop a quantity of broken,
bruised, and unmarketable potatoes which can be utilized to good
advantage as hog feed. On account of their high moisture and
relatively low protein and fat content, sweet potatoes must be
supplemented with grain, if fed to fattening hogs.
Supplemented with concentrates and pasture, sweet potatoes
are an excellent hog feed. By using approximately half the
grain that would be used with pasture alone, growing shoats
do well on this root crop. Hogs turned into the sweet potato
field after the main crop is harvested eat many small potatoes
and roots that otherwise would be wasted. Or the potatoes may
be gathered and stored and fed as needed to the hogs in troughs
or on a platform. Approximately two pounds of grain for 100
pounds of live weight of hogs, added to a ration of sweet potatoes,
will produce satisfactory gains.
According to an experiment reported in Florida Experiment
Station Bulletin 90, when the ration was entirely of sweet pota-
toes the hogs became unthrifty and actually lost weight after
being fed 42 days.

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