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Issued July 9, 1913.
U. S. DEPARTMENT OF AGRICULTURE.



FARMERS' BULLETIN 542.





CULTURE, FERTILIZATION, AND FROST

PROTECTION OF CITRUS GROVES

IN THE GULF STATES.





BY

P. H. ROLFS,
Director of the Agricultural Experiment Station of Florida.


WASHINGTON: -
GOVERNMENT PRINTING OFFICE.
1913.












LETTER OF TRAN SMITTAL.


U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF PLANT INDUSTRY,
OFFICE OF THE CHIEF,
Washington, D. C., April 11, 1913.
SIR: Many requests are received at the Department of Agriculture
for information on the methods employed in growing oranges and
other citrus fruits in Florida and the Gulf States, and it is important
that the Department be able to supply the desired information as
fully as possible. In order to furnish this information in concise
form, Prof. P. H. Rolfs, Director of the Agricultural Experiment
Station of Florida, has revised Farmers' Bulletin 238, entitled Citrus
Fruit Growing in the Gulf States," and has divided the material
contained in that -publication into three parts, of which this paper
is the third, as follows: Sites, Soils, and Varieties for Citrus
Groves in the Gulf States "; Propagation of Citrus Trees in the
Gulf States "; Culture, Fertilization, and Frost Protection of Citrus
Groves in the Gulf States." In this form the information will be
more available for distribution in the territory directly concerned and
will be of more service, it is believed, to prospective growers of
citrus fruits and to planters already engaged in this industry. I have
the honor to recommend that the paper be published as a Farmers'
Bulletin.
Respectfully, WM. A. TAYLOR,
Chief of Bureau.
Hon. D. F. HousToN,
Secretary of Agriculture.
542






















CONTENTS.

Page.
Introduction...... --...- -.. ..---- - -- --- ...................... 5
Preparation of the land-....................................-------------------------------------............ .5
Setting out trees....---- ----......--....-.......-------------------------------------...... --.....-- 6
Time and manner of setting ou rees............................ .... 6
Catch crps................... ... ... .....................----------------------------------- 7
Pruning-----....-----------------------------........ ..---------- .......----------- 7
Fertilizers-................... ......... . .. 8
Commercial fertilizers for Florida -..---..--........-----------------.................... 8
Stable manure of doubtful utility-------------..................................... ----------11
Injurious action of muck....................................---------------------------.......... ------------12
-Protection against cold ....--...---------------------.....--------------........... 12
Protection by heat ........ --------------------..............................-------------............ 12
Fuel oils ............... ... .... 13
Heaters.--.....-------------------------------.................. ---------.... ................ 13
Storage tanks........ ---------------- ------------------------.......... 15
Cost of heating........----...................................---------------------------------------......... 15
Wood fires ...... ------------- -------------------------- -------- 16
Protection by irrigation................................................. -------17
Protection by sheds-------------..-.....--...........-------------------------............... 17
Top-working ........................................... ..-- .......... ...... 18
Crown-working- ................................................. ........... 19
542 3




7 "


ILLTJSTR NATIONS.

Page.
FIG. 1. Crown-grafting an old orange stock ................................... 18
2. Ruby orange bud, inserted May 21 on a sprout from an old sweet-orange
trunk, as it appeared on October 25..-......--...-.....---------..........-----------..... 19
3. Ruby orange crown graft, inserted March 1, as itappeared on October 23. 20
542
4








B. P. I.-890.

CULTURE, FERTILIZATION, AND FROST PROTEC-

TION OF CITRUS GROVES IN THE GULF STATES.


INTRODUCTION.

The growing of citrus fruits, an industry which has attained vast
proportions in Florida, is receiving much attention in other Gulf
States. The purpose of this bulletin is to answer some of the many
inquiries constantly received by this Department and to act as a
general guide for prospective planters who need definite advice upon
questions of citrus-fruit growing. The information is necessarily of
a very general character, but the essential factors are presented in a
manner which, it is hoped, will enable planters to understand fully
the fundamental principles involved.1
PREPARATION OF THE LAND.
As a rule, the field chosen to be planted out to an orange grove is
land with a native growth upon it. Usually the land is covered with
forest trees. Various devices have been used for reducing the amount
of labor necessary to get rid of this native growth, but up to the
present time no substantial or decided progress has been made in
the methods of clearing land. The most of the work is done by main
strength and muscular labor. Where the native growth happens to
be some form of hard wood, it is the usual practice to remove the
trees and stumps. Some advantage is frequently obtained by the use
of dynamite or other explosive in loosening the stumps. Where
the native growth is pine woods or palm trees, the necessity for
removing the stumps is not so great, though in the case of the former
the stumps are usually taken out. In cabbage-palmetto hammocks
some of the trees are left and used as nurse plants for a few years.
The most economical course is to remove all trees, shrubs, and
other forms of vegetation from the land and to clear it of all rocks
and any other debris that may be found. Then the land may be
broken up and put into a first-class state of tilth, which will permit
careful staking and planting.
1 For a discussion of other phases of this problem which can not be included here, since
to treat them adequately would unduly increase the size of this bulletin, see Farmers'
Bulletins 528, Sites, soils, and varieties for citrus groves in the Gulf States; 539, Prop-
agation of citrus trees in the Gulf States; and 172, Scale insects and mites on citrus
trees.







6 CULTURE OF CITRUS GcRiO'E IN GULF STATES.

SETTING OUT TREES.

Usually the prospective orange grower buys trees from a nursery
and sets them out as soon as the field has been cleared, wishing, of
course, to get the trees on the land as soon as possible and to hasten
the time when he may be selling fruit. Sometimes this is by no means
the most profitable procedure. Land especially rich in organic matter
and heavily matted with roots from the native growth would be
decidedly better for having produced a crop or two of vegetables
before the grove is planted. If for any reason it is not desirable to
grow vegetables, a crop of weeds grown on it for a year would do
much to sweeten the land preparatory to receiving the trees. A
crop of cowpeas or velvet beans would be preferable, however.
The number of trees to be set out to the acre depends on the variety
selected and the character of the land. Large-growing citrus trees,
such as pomelos and the Valencia Late and 'Hart sweetforanges,
should not be set closer than 100 to the acre, and on first-class soil
80 are enough. Smaller growing varieties, such. as the mandarin
group of oranges and the limes, should not be set closer than 200 trees
to the acre. The character of the land will also need to be consid-
ered in setting out a grove., In a sandy loam rich in organic matter,
especially in southern Florida, trees grow much more vigorously and
in consequence should be set farther apart. Forty-nine trees to the
acre, i. e., setting them 30 feet apart each way, is about as small a'
number as one can afford to plant, In the heavy clay soils trees
grow less vigorously and may be set nearer together.

TIME *AND MANNER OF SETTING OUT TREES.
The time of setting out trees will depend on the location and the
conditions. In the West Indies and south Florida trees may be set
out at any time of the year when the land is ready and when there
is sufficient moisture to favor their growth. In central Florida, the
spring (February and March) is preferable. The same is true of
north Florida, Louisiana, and Mississippi. In the extreme northern
portions of the citrus-growing section it is usually better to wait
until the danger of freezing weather is. past. This will bring the
date up to about the latter part of February. In setting out trees
from the nursery, care should be taken to injure the roots as little
*as possible. Where trees can be taken up with a considerable ball
of earth and transplanted in this way, they may be set out without
any apparent check in growth. This, however, is not usually prac-
ticable.
When the trees are taken up, the roots should be carefully pro-
tected by means of wet cloths or moist moss and the trees set in holes
542





CULTURE OF CITRlTU lTE' IN GULP STATES. 7

already prepared for them. If the ground is not already very moist,
the addition of one or two pails of water will usually puddle the
roots and cause the trees to grow promptly. At the time of setting
out, the tops should be cut back to correspond closely to the condition
of the roots. Complete defoliation is also advisable. The favorite
size of tree to set out is one that has grown about 4 feet tall in the
nursery and has several branches. Such trees are usually about an
inch or an inch and a half in diameter at the crown.
CATCH CROPS.

As soon as the field has been set to a grove, cultivation may be
begun. The kind and amount of cultivation will be determined by
the character of the soil. Light, sandy soil should have shallow but
careful cultivation. Heavy clay soils need thorough and deep
working. Where there is an abundance of moisture supplied natur-
ally to the soil, other crops may be grown to advantage. Where
the soil is inclined to be dry and irrigation has to be practiced, inter-
cropping is of doubtful utility. During the winter, vegetables may
be planted and cultivated as in ordinary fields with decided advan-
tage to the orange trees, unless the land is too dry. Leguminous
cover crops may be planted as soon as the spring and summer rains
begin. When fall droughts occur the cover crops will have to be
removed .to conserve the moisture of the soil. Cultivation should
then be resumed. If the soil is inclined to be sterile the cover crop
should be used as a mulch for the trees. If the ground is sufficiently
fertile to permit it, the cover crop can be utilized for hay.

PRUNING.
"To prune or not to prune; that is the question." At many of the
meetings of the horticultural societies the question of pruning has
been vigorously discussed. There are many good reasons for pruning
trees; on the other hand, there are reasons why trees should not be
pruned. The question, then, must be decided by each individual.
One poinIt,, h'weiver, has been very well settled, and that is that low-
headed trees are preferable. Twenty-five or thirty years ago it was
a common practice to have citrus trees trimmed high enough to permit
a man to drive a cultivator under the branches. The severe cold of
several winters has caused this custom to be very largely abandoned.
In the southern part of Florida, where there is no danger from frost,
it has been found that shading the ground by the limbs has been very
beneficial to the grove. Another important advantage in low-headed
trees is that the fruit may be gathered much more cheaply than from
tall trees.
542






8 CULTURE OF C'iTRU:Fl IN GULF STATES.

Nearly all orange growers :- 'r.- that the pruning out of dead
and worthless branches is of benefit to the tree. The extent to which
sound wood is pruned out, however, varies with the notions of the
individual grower. Some of the most extensive and best growers in
Florida practice no pruning at all. Diseased branches should always
be cut out, removed from the orchard at once, and burned. Sprouts'
that start from below the bud must be removed, and this should be
done as soon as possible. Water sprouts arising from the trunks and
larger branches should also be removed.
A citrus tree should be kept in a low, compact form, but violent
pruning, such as is often practiced in deciduous fruit orchards, is
not only unnecessary but often absolutely harmful. Systematic
pruning for special purposes is often necessary, but it must be done
by a well-directed effort or more harm than good will result.

FERTILIZERS.

Under the general heading of fertilizers may be considered ma-
terials which are employed to enrich the soil or cause it to produce
a heavier crop. Ordinarily the term fertilizers is restricted to
such as are considered commercial articles, while the term manure "
is applied to organic offal and refuse accumulating on the farm. In
some parts of the United States the term "guano has been used
to designate commercial fertilizers. Cover crops which are grown
on the land for the purpose of enriching the soil are frequently
called "green manures."
The kind of fertilizer required to produce a heavy crop of oranges
varies greatly. In the West Indies, Mexico, Mississippi, Louisiana,
and California the general constitution of the soil is so variable that
no hard-and-fast rule can be given. In fact, in many cases it is doubt-
ful whether the desired results attend the application of any or all
the elements usually needed as plant food. While fertile soils produce
trees of vigorous growth which often bear large crops of fruit, the
possibilities are necessarily limited to what Nature will do; but in
soils where one or more of the elements of plant food are1._I1e? nt in
insufficient quantity, the modeling of the fruit and the pr1oiductioi of
excellent qualities are more completely under the control of the
skilled horticulturist.
COMMERCIAL FERTILIZERS FOR FLORIDA.
The kind and quantity of fertilizer necessary to produce a maxi-
mum crop of fine fruit depend entirely upon the soil in which the tree
is growing. Many soils in the citrus regions contain an excess of all
the elements necessary for the production of citrus fruits. When fer-
542






CULTURE OF CITRUS GROVES IN GULF STATES. 9

tilizers are applied under such conditions no beneficial effect can be
noticed from their use. An orange tree planted in soil that contains
large quantities of the necessary elements usually produces large
fruit, but often of an indifferent character. Soils that are deficient in
nitrogen, potash, and phosphoric acid can usually have these supplied
from such sources and in such quantity as will produce fruit of the
desired texture and consistency. It therefore happens that the finest
and most delicious fruit is grown on rather sterile soil.
The entire piny woods of Florida may be said to be deficient in
each of the three important elements of plant food-nitrogen, potash,
and phosphoric acid. Soils are also found in which there is a defi-
ciency of lime, so that frequently an addition of this element will
prove of value. The hammock soils are usually sufficiently fertile to
produce at least one crop, or even a few crops of fruit, without the
addition of fertilizer. These, however, in time become depleted, and
the elements of plant food then need to be supplied by substances
from a commercial source.
In growing citrus fruits on soils that are deficient in all of the
three important elements of plant food, a fertilizer of the following
composition is desirable:
Per cent.
Ammonia ------------------------------------------------- 4
Potash ---------------------------------------------------10
Phosphoric acid (available) --------------------- 6
For growing nursery stock or for trees not of a bearing age the
amount of potash in the formula may be reduced to 6 per cent, leaving
the two other ingredients in about the above proportions.
The quantity of this fertilizer to be applied per acre will depend
upon various conditions. About 15 or 20 pounds per year may be
applied to each tree capable of producing 10 boxes of fruit, the
quantity being decreased. or increased from year to year, as results
indicate. Calculating this on the basis of 100 trees per acre, 1,500.
pounds per acre per year would be used for young bearing trees.
Double this amount is very frequently applied, and sometimes three
times as much is used.
The following table gives approximately the amount of material
needed per acre for bearing trees to supply a quantity of fertilizer
equal in fertilizing constituents to 1,500 pounds of the foregoing
formula:
Pounds.
(1) Sulphate of ammonia --------------------------------- 250
Sulphate of potash, high grade 300
(2) Or sulphate of potash magnesia (low-grade sulphate of
[ potash) ------------------------------------------- 550
(JDissolved boneblack ------------------------------- 550
(Or acid phosphate, 14 per cent available phosphoric acid- 850
90578-Bull. 542-13-- 2







1U CULTURE OF CITRUS GROVES IN GULF STATES.

In the case of nursery stock and growing trees, 2 per cent of the
ammonia may be derived from an organic source. This would require
approximately the following ingredients:
Pounds.
(1) Sulphate of ammonia ------------------ 125
(2) Dried blood --------------------- 100
f Sulphate of potash, high grade --- --------------200
(3)j Or sulphate of potash magnesia (low-grade sulphate of
potash --------------- 350
(4 Dissolved boneblack ----------------------- -- 550
( Or acid phosphate, 14 per cent available phosphoric acid-- 850
If there is any tendency toward die-back the dried blood should be 2
omitted and the amount of sulphate of ammonia increased to 250
pounds. If a quick-acting fertilizer is wanted, nitrate of soda (100
pounds) may be employed in place of dried blood.
Citrus-fruit growers wishing to' compound their own fertilizers
should give due regard to the substances from which the different
qualities are derived.
Organic ammonia, as found in cottonseed meal, dried blood, guano,
and the various stable manures, is likely to produce a soft, rapid
growth, and in certain sections, especially in Florida, its continued
use is almost certain to produce die-back.
Nitrate of soda is soon taken up by the trees, but is easily washed
out of the soil. Where it is used as the only source of nitrogen it
has to be repeated from four to eight times each year, varying with
the amount of rainfall and the character of soil.
Sulphate of ammonia is much slower in becoming available to the
trees and seems to be retained in the soil much more tenaciously than
nitrate of soda, so that it need not be applied oftener than two to
four times a year.
'In the use of potash there is very little choice between the low-
grade sulphate, which is also called the double salts of potash and
magnesia, and the high-grade sulphate of potash.
In selecting ]pil.-,phlite-, preference is given to dissolved bone or
dissolved boneblack over dissolved rock phosphate, although some.
experienced orange growers consider the phosphoric acid derived
from dissolved rock as good as that obtained from dissolved bone.
Thomas slag may be employed to good advantage, especially on soils
giving an acid reaction.
The ammonia is washed out of the soil in great quantities by fre-
quent and heavy rains. Potash is washed out to a less degree and
phosphoric acid only to a slight extent, while lime, or calcium, is lost
in large quantities. The quantity of these elements lost will vary
according to the nature of the soil and the amount of heavy rainfall
occurring. The ideal way of fertilizing would be to make an appli-
cation of phosphoric acid in the spring before the rainy season has
542







CULTURE OF CITRUS GROVES IN GULF STATES.


begun; to make two applications of potash-one in the early spring
at the time of applying the phosphate and another in the fall after
the rainy season has passed; and to make four or more applications
of ammonia-one with each application of the potash and two or
more at equal intervals between, except during the dormant winter
season.
The following example will serve to illustrate" the point: Let us
suppose that a grove needs 1,500 pounds of fertilizer per acre per year
of the normal formula, that is, 4 per cent ammonia, 10- per cent potash,
and 6 per cent phosphoric acid. In the spring, therefore, before the
rainy season has begun, we would apply the entire allowance of phos-
phoric acid, or 850 pounds of 14 per cent acid phosphate; one-half
the potash, or 150 pounds of high-grade sulphate of potash; and one-
fourth the ammonia, or 624 pounds of high-grade sulphate of
ammonia. These ingredients may. be mixed and applied in the usual
way. Care must be exercised, however, since such a mixture is a
very concentrated fertilizer, and if applied in a narrow zone around
the tree injury may result when the weather conditions make possible
the too rapid assimilation of the chemicals or when the nature of the
soil itself is such that the fertilizer is taken up too quickly.
For the fall application, 150 pounds of high-grade- sulphate of
potash should be mixed with 692 pounds of high-grade sulphate of
ammonia. The remaining 125 pounds of sulphate of ammonia should
be evenly divided and applied as the conditions indicate. In .this
way the amount of plant food that is contained in 1,500 pounds of
fertilizer of standard formula would be applied during the year.
The proper regulation of the amount of ammonia to be applied
is the greatest difficulty in preparing a complete fertilizer formula.
The presence of this element in too large or too small quantities in
the soil' or in the fertilizer appears to give more trouble than any
other ingredient. Groves are very frequently injured by large appli-
cations of ammonia. A very common practice is to make only two
applications a year of a complete fertilizer-one during the spring
and one during the fall. Other growers make three applications-
one during the early spring, one later in the spring, and another
during the fall.
STABLE MANURE OF DOUBTFUL UTILITY.'
The benefits of stable or barn manure, which is largely used by
many growers, are also very doubtful. The fruits produced by nitro-
gen from this source are usually large, coarse, thick-skinned, and of
) inferior flavor.; If barn manure is used, however, each tree should
receive only a small quantity, and where it is the main element of
fertilization liberal dressings of potash should occasionally be applied'
to counterbalance the nitrogenots fertilizer.
1 See Yearbook, U. S. Department of Agriculture, for 1894, pp. 195 and 196.
542







12 CULTURE OF CITRUS GROVES IN GULF STATES.


INJURIOUS ACTION OF MUCK.1

Some growers claim that since muck is largely decaying vegetable
matter it should be applied to the grove in large quantities, either
raw or composted with sulphate of potash, etc. While this has occa-
sionally given excellent results, its extensive use has often done
serious injury. In order to obtain a smooth, thin-skinned, juicy
fruit with few or no seeds, we must vary the fertilization which the
plant receives in its wild state. The tendency of all organic manures
rich in nitrogen is to stimulate large, sickly growth. Groves which
have had liberal dressings of muck are frequently much diseased;
their crops are light, the oranges coarse, thick-skinned, and sour, the
fruit drops prematurely, and the trees are often affected with die-
back. What has been said of muck applies to a greater or less extent
to the various forms of organic nitrogen used.
What has been said about the effect of muck and barn manure on
the quality of the fruit applies equally to the effects produced by
cottonseed meal, blood and bone, tankage, etc. In general, organic
fertilizers do not stimulate fruiting to the same extent as the'mineral
fertilizers.
PROTECTION AGAINST COLD.
The disastrous freezes of 1894, 1895, and 1899 in Florida and those
of 1912 and 1913 in California have caused the orange grower to cast
about for some means of protection against a sudden cold wave.
Two general methods have been practiced: The first is that of
warming the air without providing shelter and the second is that
of providing a shed or shelter for the trees.
The methods of raising the temperature by means of fires, as de-
scribed in the following paragraphs, can not be relied on if the
cold weather is accompanied by high winds or rainfall. In a por-
tion of Florida during the heavy freeze of 1899 not only a heavy
rainfall but heavy winds accompanied the cold. All attempts at
building fires were useless, and even if they could have been built
the wind would soon have carried the warm air out of the groves.
When a very moderate breeze is blowing and the temperature
falls only 4 or 5 degrees below the danger point, fires should be
increased on the windward side, perhaps doubled, at the expense of
those in the interior, but fires should not be extinguished in the
interior of the grove, merely reduced.
PROTECTION BY HEAT.
The burning of different kinds of fuel in an orchard for the
purpose of raising the temperature has been employed a great many
1 See Yearbook, U. S. Department of Agriculture, for 1894, pp. 195 and 196.
542







CULTURE OF CITRUS GROVES IN GULF STATES.


times. The success attending the work varies under different cir-
cumstances and with different conditions. When the drop in tem-
perature is accompanied by a heavy windstorm and rain or sleet,
it is almost impossible to accomplish anything in the way of orchard
heating. Fortunately, freezing weather in the citrus regions is
usually accompanied by a rather still atmosphere and freedom from
rain or snow.
A great many. kinds of fuel have been employed for orchard heat-
ing. Wood was probably the first, and it is still employed to some
extent. Coal, coke, and fuel oil have all been used to a greater or less
extent. Each of these fuels may have special advantages over others
in some particular place. In general, it may be said that the fuel-oil
method has given satisfaction more frequently than all the others
combined. To discuss all of the methods fully is quite beyond the
purpose of this bulletin.
FUEL OILS.

This term includes a variety of materials known under many
different trade names. In general, they are the heavy residue left
after the lighter oils contained in the petroleum have been removed.
A fuel oil known as crude oil is said to contain a large quantity of
asphaltum, which becomes quite troublesome. The asphaltum re-
mains as a residue in the bottom of the heaters and interferes with
the heating when the fuel burns low.
HEATERS,

The varieties and styles of heaters offered by the trade are nearly
as numerous as the varieties of fuels. Usually the more complicated
in construction the heater is, the less efficient it becomes in its prac-
tical work in the orchard. Even a 10-pound lard pail, holding
more than a gallon of fuel oil, compares very favorably in efficiency
with the patented heaters, in some cases even proving superior to
them. The lard-pail type of heater, made from heavy sheet metal
and holding about 5 quarts of oil, can usually be purchased
from heater manufacturers at 10' or 12 cents apiece when ordered
in carload lots. In this type of heater the quantity of fuel used
and the heat given off decrease gradually as the supply in the heater
is consumed.
The lard-pail type of heater holding a gallon of fuel oil will burn
for 3j to 4 hours, varying with the kind of fuel oil used and weather
conditions, giving off about one-half as much heat toward the close
as at the beginning of the charge. When a soot arrester is used, the
quantity of fuel consumed in an hour is much reduced, but at the same
542







14 CULTURE OF CITRUS GROVES IN GULF STATES.

time a correspondingly smaller amount of heat is given off. There
are a number of heaters that hold a much larger quantity of fuel oil.
Most of these are so constructed, either by means of a soot arrester or
otherwise, that the quantity of oil burned can be regulated. Ordi-
narily these are to be preferred to the smaller type, since when freez-
ing weather occurs it, is usually of more than four hours' duration.
The minimum temperature is very likely to occur about sunrise.
Refilling in the dark is difficult and wasteful.
The type of heater with a sliding top to regulate the area of the
burning surface has worked quite satisfactorily. Roughly speaking,
44 square inches of free burning surface will consume a gallon of fuel
oil in four hours. It has been pretty clearly demonstrated by experi-
ment that it will require the same quantity of oil to raise the tem-
perature 5 degrees in an orchard, whether few or many heaters are
used. When many heaters are used the temperature in .the orchard
can be maintained much more'evenly. The number of burners needed
per acre to raise the temperature 5 degrees will vary greatly, accord-
ing to the favorable or unfavorable climatic conditions and the condi-
tion of the grove. A small grove of large trees closely planted and
surrounded by a dense hammock will pass unharmed through a freeze
of 250 F., while considerable damage would be done in a grove.not so
protected. Likewise, the number of heaters required in the former
grove would be fewer than in an open grove where the trees are small
and only a few to. the acre.
From 50 to 100 heaters and from 100 to 200 gallons of fuel oil per
acre for. each night when heating is necessary is a reasonably safe
estimate in a grove 7 to 10 years old. This number of heaters and
quantity of fuel oil will probably keep the temperature 5 degrees
above the surrounding atmosphere if the wind is not blowing more
than 4 or 5 miles an hour. Ordinarily the heaters are distributed
evenly throughout the grove, placing one in every center between
four trees. This requires about as many heaters as there are trees
in the grove, and is a poor rule to follow absolutely, since a grove
of small trees planted far apart will not hold the heat as well as a
grove of large trees planted closely. Every grove owner will have
abundant latitude to use his own judgment as to the effect of the
exposure of his grove and the other elements that enter into the ques-
tion of orchard heating.
Every grove supplied with heaters should have in it a thermometer
that will sound an alarm when the temperature approaches the
danger point. Such an instrument can be obtained for from $7 to
$20 from instrument manufacturers and dealers. The thermometer
should be placed in that part of the grove in which the danger from
542







CULTURE OF CITRUS GROVES IN GULF STATES. 15

frost is greatest, and the wires should run to the hpuse or central
office.
The danger point will vary with conditions. At blooming time
the danger point is highest and injury may then occur whether the
temperature goes down to 320 F. or not. Mature fruit is almost
certain to remain unharmed unless the minimum temperature falls
below 28 F. Trees in a fully dormant condition will remain un-
harmed at 24 F., but when full dormancy has passed the trees
become increasingly sensitive to cold. When in full growth, frost,
no matter at what temperature it occurs, will destroy the tender
tissues.
Every grove owner should be in direct telephone communication
with the United States Weather Bureau, in order to receive warn-
ings of probable frosts and freezes. All the important fruit-growing
sections receive this information regularly over long-distance tele-
phones.
STORAGE TANKS.
The fuel oil should be stored in a tank located preferably in the
grove. Where possible, it should be so placed as to allow the oil
to be siphoned directly into it from the car tank, and then from it
into the wagon tank. The storage tank should always be so located
as to enable one to run the fuel oil into the wagon tank by gravity.
Pumps work satisfactorily in warm weather, but are apt to be
troublesome during a cold spell. They also require extra labor, which
could be more advantageously employed in the grove. A break in
a pump will cause delay and may make the fuel inaccessible, thus
rendering the whole plant ineffective.
Fuel oil may be stored in a variety of receptacles, the least desirable
of which are barrels. Concrete tanks or cisterns with tops, such as
are constructed for holding water, will be found useful. The inner
surface should be finished with cement plaster and finally given two
or three coats of asphaltum paint. Steel water tanks are in common
use. Wooden tanks similar to water tanks, made of upright 2-inch
planks, are commonly used and seem to be thoroughly practicable.
Some grove owners have tanks such as are used on tank cars for
hauling fuel oil, but these would seem to be unnecessarily expensive.

COST OF HEATING.

The estimated cost of -preparing to heat a 10-acre grove will vary
within certain limits. No two groves would he located exactly alike
as to the cost of heating. The distance from the railroad, number
of times to be fired, and variation in price of labor all come in as
*variables.
542







16 CULTURE OF CITRUS GROVES IN GULF STATES.


The following table gives an approximate cost for a 10-acre grove:

500 to 1,000 heaters, at 40 cents -------- -- $200 to $400
One steel wagon tank -----------------------------25 to 30
Torches and gasoline can for lighting --------- 10 to 12
Thermometers and installing -----------------------12 to 25
3,000 to 6,000 gallons of fuel oil -- 90 to 180
Storage tank for fuel oil ------ -- 100 to 300
Total --------------------437 to 947

After the equipment has been installed the expense is compara-
tively light and includes mainly the annual depreciation, care of out-
fit, fuel oil burned, transfer to storage tank, and labor. The last
item will vary from year to year. When no firing is needed this item i
will be comparatively light. At firing time it will require two or
three additional men to take care of 10 acres. An allowance of $6
to $10 for each night fired should be ample, including the cost of
distributing the fuel oil for the next charge. In extensive groves
and where large-size heaters are used, one man to 10 acres will be,
sufficient to take care of the fires, but additional labor will be needed
to replenish the fuel.

WOOD FIRES.

In a wooded country the form of protection against cold afforded
by fires is cheap and at the same time very effective when a still
cold occurs. The wood is piled in the centers of the squares, vary-
ing in quantity from three or four to a half-dozen or a dozen sticks
of cord wood. When a freeze is predicted, the watchers notice the
thermometer and by the time the cold approaches within 2 or 3
degrees of the danger point, which is 280 F. for fruit and -240 F. for
foliage, fires are started in alternate squares. These will usually
heat the grove some 4 or 5 degrees. If the cold continues to increase,
all the piles of wood are started. It is of course necessary to have on
hand a reserve stock of fuel in such an emergency. Shortly after the
sun rises the next morning the temperature will usually have risen
again, so there will no longer be any danger to the fruit or trees. If
there is no favorable change in the weather, the cold on the second
night is quite likely to be more severe than on the first. Firing
then must be begun much earlier, and consequently a greater quan-
tity of wood will be needed.
Owing to the large amount of labor involved and the difficulty of
securing efficient help, this form of orchard heating has been largely
abandoned. A
542







CULTURE OF CITRUS GROVES IN GULF STATES.


PROTECTION BY IRRIGATION.

In the citrus-growing sections the water that is freshly pumped
from" the soil is quite warm, ranging from 50' to 74' F. When this
water is carried through a grove in irrigating ditches it gives off a
considerable amount of heat and has been used effectively in some
instances where the temperature has fallen but slightly below the
danger point.
Arrangements have also been made to throw this water into the air
from spray nozzles. This is somewhat more effective than when the
same quantity of water is carried through irrigating ditches, but can
not be relied: upon as being sufficient during extremely cold spells.
During one cold wave the orchard of Mr. Theodore Mead, at Oviedo,
Fla., was protected in this way. During one night the temperature
fell considerably below the freezing point. The next morning the
trees were so heavily coated with ice that some of the branches broke.
The following summer the trees bore a crop of fruit.
The waters from artesian wells have also been used for the purpose
of warming citrus groves, this water being quite warm, running into
the sixties usually and as high as 740 F. in some wells. While this
use of water does some good and protects that portion of the grove
in the immediate vicinity of the large flow, the amount of heat given
off is small and the volume of water supplied is not considered large
enough to protect the grove during severe freezes.

PROTECTION BY SHEDS.

The most successful method of protecting citrus trees from
extremely cold weather is that of building a shed over the grove. At
first thought this would seem to be entirely too expensive and not at
all feasible, but the sheds have now been used long enough to demon-
strate fully that they are not only possible but practicable. There
are several modifications of the shed.
This method was successfully'employed immediately after the great
freezes and was profitable while Florida oranges brought a high price.
Orange sheds now occur to a limited extent and only in regions
where great damage from cold formerly occurred. These sheds are
simple structures, having a flat roof or cover held up by posts. The
posts are properly braced and hold the cover from 12 to 16 feet above
the ground. Some of the movable tops are made solid,while those with
stationary tops are made of slats or laths so placed as to give either
a half or third shade.
542







18 CULTURE OF CITRUS GROVES IN GULF STATES.

TOP-WORKING.
It sometimes happens that a grove is planted out to a variety that
does not prove prolific, or one that may be unprofitable to market.
In such a case it becomes necessary to abandon the grove or to top-
work the trees. With the trees in a healthy and vigorous condition
most or all of the top should be removed, only two or three vigorous
limbs being left. Buds of the desired variety may be inserted into
the remaining limbs. This cutting away of most of the top causes
a heavy flow of sap intb the smaller limbs which remain. In such
cases the buds will "take" where they would fail if the top of the
tree had not been vigorously cut back.
Another way of top-working is to cut away nearly all of the top
and then wait for sprouts to start. After the sprouts have reached a





I t
ill- I














FIG. 1.--Crown-grafting an old orange stock: a, Base of scion, showing
slanting cut; b, method of inserting scion. (From 'Yearbook, U. S. De-
partment of Agriculture, for 1895.)

size of about half an inch in diameter they may be budded, and the
bud will take readily. When trees have been cut back severely, the
bodies and the larger limbs should receive a heavy coat of whitewash
to protect them against sun scalding.
Before top-working, the orchardist should be well acquainted with
his grove and soil. In a very large portion of Florida severe top-
pruning results in die-back unless proper fertilization and soil treat-
ment accompany the work.
In California and Louisiana it appears to be safe to remove the
entire top and to work buds into the large limbs. For top-working,
the shield bud and sprig graft may be used to best advantage.
542






CULTURE OF CITRUS GROVES IN GULF STATES.


CROWN-WORKING.

At times it becomes desirable not to permit the body of the tree to
remain. In such cases it may be cut off at the ground line. Some
citrus trees, especially limes, resent treatment of this kind and fail
to grow after the top has been entirely cut off. The ordinary citrus
stock, however, is almost certain to sprout again if treated in this
way. Large areas, 20 to 40' acres in extent, were sprouted in this
way after the great freezes
of 1894 and 1895 in Florida

healthy stump. .
Trees that have been cut .
back in this way may be
crown-worked or crown-
grafted, as illustrated in
figure 1, the sprig being in-
serted in the portion of the
crown that will take it most
easily. By slipping the
scion into the portion of the
crown where the bark may
be raised without breaking, .
the work may be done with-
out the use of wax or other
binding material. After
the scion has been inserted,
moist earth should be raked
over the crown and around
the scion, covering them
until they have "taken," FIG. 2.-Ruby orange bud, inserted May 21, on a
and then exposing the tips. sprout from an old sweet-orange trunk, as it
'Where this work is done by appeared on October 25. (From Yearbook, U. S.
Department of Agriculture, for 1895.)
experienced hands, only a
very small percentage of the crowns fail in taking one or more sprigs.
Those that fail to take may be worked again or left to produce sprouts
and then budded into these sprouts. By using three or four such
scions in a crown 4 or more inches in diameter and doing the work
during February or the early part of March the percentage of loss
sustained will not be very great.
Another method of renewing such an orchard is to wait until the
sprouts have started from the crown or the main roots. After these
sprouts have reached a size of half an inch or so in diameter, buds are
inserted as low down as practicable. In doing this, however, a con-
542






20 CULTURE OF CITRUS GROVES IN GULF STATES.

siderable loss ,f time will be sustained in waiting, first, for the
sprouts to start and then, again, in cutting them back to make the
buds sprout. The loss of time is strikingly illustrated by the two


FIG. 3.-Ruby orange crown graft, inserted March 1, as it appeared on October 23.

accompanying figures made from photographs (figs. 2 and 3)..
This method of budding sprouts, although it results in some loss of
time, is nevertheless very commonly used by growers because of its
convenience.
542





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