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Copyright 2005, Board of Trustees, University
GULF COAST STATION MIMEO REPORT 56-2
FERTILIZING GLADIOLUS S' P 30 5
S. S. Woltz, Assistant Horticulturist
No single fertilizer recommendation can be made for gladiolus for all condi-
tions under which they may be grown in Florida. It is probably best, therefore, to
select a general fertilizer program that will insure against serious deficiencies
-r excesses of the various nutrient elements, and then vary the program to meet
Generalized Fertilizer Recommendation
The following applications of fertilizer makes up a general program to be va-
ried according to needs, as discussed later in this report.
1. 400 pounds of 4-8-8 containing secondaries, mixed in the bed. Nitrogen sour-
ces are specified as 25 percent organic, 40 percent nitrate, and 35 percent ammoni-
acal. The secondary elements and the percentages to be supplied in the 4-8-8 ferti-
lizer are: 1 percent water soluble MgO, 0.5 percent Fe2 0 0.5 percent MnO, 0.2
percent CuO, 0.2 percent ZnO, and 0.2 percent B103. Notes: If dolomitic limestone
is not used in conditioning the land, then increase MgO to 2 percent in applications
1 and 2. ZnO and MnO may be reduced or omitted if furnished in fungicidal sprays
2. 500 pounds of the above mixture sidedressed and worked into moist soil about
3 weeks after planting.
3. 400 pounds of 5-10-10 containing 0.2 percent B203, with nitrogen from inor-
ganic sources, approximately 60 percent ammoniacal and 40 percent nitrate. This
is to be applied two weeks after No. 2 above.
4. 400 pounds of the mixture in No. 3, applied two weeks later.
5. 200 pounds of 8-0-16 with 50 percent nitrate and 50 percent ammonium nitrognr
and 0.2 percent EBp, to be sidedressed immediately following the completion of
If the grower prefers to use only one fertilizer mixture, he may vary the
formula given for applications 1 and 2 by halving the percentages of secondary ele-
rsnts, except for B203 which should not be reduced. This mixture may then be
applied at the rate of 400 pounds mixed in the bed, followed by three 500 pound
sidedressings before flower harvest and another after flower harvest.
Factors Determining Fertilizer Needs
Following is an outline of the factors affecting fertilizer requirement of
I. Soil Conditions.
1. Fertilizer retaining capacity
If the soil has a high cation-exchange capacity, or in other words, is a
heavier soil than the sands, nutrient elements other than nitrates are retained
somewhat against leaching. This is true in mucks and certain phases of Bladen
and Manatee soils, for example.
In heavier soils it will be possible to omit one of the fertilizer applica-
tions or to reduce the amount of each application. Also, the fertilizer analy-
sis may be adjusted on the basis of important reserves of nutrients in the soil
or on -.he basis of the fertilizer retaining capacity of the soil, With most
gladic.us soils, however, there is not generally any large reserve of nutrients
at planting time.
The lc.,r the moisture-holding capacity of a soil, the greater will be the
loss of nr.i-rients to leaching. Irrigation or rain water carrying dissolved nu-
trients vijll move them out of the root zone before the roots have a chance of
absorbing a good share of the fertilizer application. The remedy for the loss
of nutrients due to excessive drainage is more frequent application of ferti-
l2zer, repeating fertilizer applications made just before heavy rains, and ar-
rsnging :irrigation to cause the least leaching loss. In order to reduce this
loss of nutrients in irrigation water it is desirable to avoid the practice, as
r;Lh as possible, of saturating the soil to a very high level and then quickly
dra.iining it out. With heavier soils containing greater clay and organic matter
contents, more of the water from a given rainfall or irrigation is retained in
thl root zone.
2. Root Disturbances.
Any factor that limits the expansion and functioning of the root system de-
creases the efficiency of applied fertilizer and thus makes special treatments
necessary, in the form of increased rates of fertilization, nutritional sprays,
and variations in fertilizer placement and irrigation to bring the nutrients
to the damaged root system. The factors that are known to damage the roots are:
nematodes, fuigi, and toxic levels of chemical elements in the soil.
Preliminary experience with soil 6terilants such as Crag Experimental Fungi-
cide 974 and Vapam indicates that the response to fertilizer will be different
when they are effectively used on soils infested with destructive fungi and nema-
todes. The root system will be more extensive and there will be more active
feeder roots which will result in greater uptake of nutrients, both native and
applied. In many soils that have been repeatedly planted to gladiolus, the roots
are much restricted by nematodes and fungi working together and the growth of the
tops of plants is limited by the poor up-take of fertilizer.
cr-tiliier experiments have shown that it is necessary to use more fertilizer
to get nor-mal flower and bulb production when damage by fungi and nematodes to
roots is serious. Little or no fertilizer under these conditions resulted in
extremely low flower production as well as poor bulb production. The use of
abnormally high levels of fertilization, such as one ton of 8-8-16 per acre
resulted in greatly improved yields, but these yields were still sub-normal.
The formulation of fertilizers will need to be changed when partial soil
sterilization is practiced, in order to compensate for the temporary decrease
in conversion of organic nitrogen to ammoniacal compounds and also the conver-
sion of the latter to nitrates. Thus, fertilizers for partially sterilized
s-il should contain more nitrate and less organic and ammoniacal nitrogen, at
lost during the first month or so after treatment.
Two other types of root disturbances encountered are physical damage from
cnlt', i;vion operations and chemical burn by concentrated fertilizer applications
in the root zone. The first of these is avoided by cultivating with sweeps set
so they will do the least amount of root pruning while still providing effective
weed~6ntrol ..To reduce fertilizer birn onj;dots; distribute :the application in
a fairly wid6 bandiand work into moist soil.
3. Soil pH
Low soil pH values, especially below 5.0, cause increased leaching of most
nutrient elements and thus decrease the efficiency of applied fertilizer. Where
accumulated soil copper causes toxicity to plants, such toxicity is much worse
at lower pH levels and may be reduced by adequate liming. Very high pH levels
reduce the availability of minor elements, except molybdenum, to plants. It is
desirable to keep the soil pH within the range of 5.5 to 6.5. In order to do
this, pH measurements should be made well in advance of planting and liming ma-
terials should be applied in time to allow them to react. The nature of the
soil and the liming material will determine the length of time required. Con-
sult Florida Circular S-39.
Frequently, after applying fertilizer at the beginning of the crop season,
it is found that the pH will drop a half to one unit below the value found be-
fore fertilizing. The 'alcitim. cllbride'lmethod4.f' detenmting' soil pH perriss
the tise of larger amounts of lime when needed for soils with greater reserve or
ez'.hangenr.le acidity. Soils that have been fertilized regularly do not usually :.
have lae-e reserve aciditygcontent, while heavier soils that are being cultivated
for the first time usually do.
1,. Climatic Conditions.
Cold, wet weather decreases the rate at which organic nitrogen becomes avail-
Oble to plants. Consequently, nitrogen supplied to gladiolus in such weather
should be derived mainly from inorganic sources, especially nitrate. Nitrate of
potash or soda to supply 15 to 20 pounds of nitrogen per acre is frequently ben:-
fl.ial during periods of cold, wet weather, as a supplement to the regular ferti-
In warmer weather, especially when considerable rainfall is expected, a great-
er percentage of the nitrogen should be furnished from ammoniacal and organic
sources to reduce leaching losses. Organic nitrogen requires time to become a-
vailable, however, and applications made near the flowering sta-e may be only
partly available before flowers are cut. Special care should be exercised with
the placement of fertilizers containing organic nitrogen to be sure that the
fertilizer will be in contact with moist soil since moisture is necessary for
the breakdown process.
The effect of rainfall on fertilizer practices is discussed under other sec-
tions of this report, but it should be emphasized that during long dry periods
special care must be taken to insure that sufficient moisture is present to dis-
solve the fertilizer. Otherwise, it may lie dormant and several applications
may accumulate to become available at the same time following a good rain, with
undesirable effects. Irrigation and placement methods should be coordinated to
insure the fertilizer coming in contact with moist soil.
III. Quality of Irrigation Water.
Very little work has been done on this subject as it pertains to gladiolus,
but it would be well to discuss it briefly on the basis of available information.
The total salt content of irrigation water should be below 1800 ppm for best
results. If possible, it is better to use wells with high salt content in the
late su.mimeb and early fall and those with lower salt content in the winter and
spring since rain in August, September and October will leach salts and also
mrke it unnecessary to irrigate so often.
The chemical nature of the salts in the water has a bearing on fertilizer
practices to be employed. Large amounts of sodium and chloride are especially
undesirable. The effects of calcium, magnesium, sulfate, and bicarbonate ions
are not as serious. To compensate for high sodium, the grower should broadcast
1000 pounds of gypsum per acre to prevent an unbalance in calcium nutrition. The
general level of potassium and magnesium required will also be increased somewhat
since sodium competes both in the soil and in the plant with these elements.
The degree of damage resulting from Fusarium bulb rot is affected by ferti-
lizer practices and this should be considered in planning the fertilizer program.
High levels of nitrogen will increase the incidence and severity of Fusarium
bulb and neck rot. Certain sources of organic nitrogen, such as blood tankage,
mixed in the bed will have an especially bad effect. Low levels of phosphorus
will also increase the attack of Fusarium. Theoretically, calcium and potassium
in good supply should decrease the susceptibility while high chloride should
increase it. Other diseases attacking bulbs and leaves are probably also made
worse by high levels of nitrogen and ameliorated by the presence of adequate
calcium and potassium.
Since Fusarium bulb rot is the most serious disease problem, the nitrogen
supply must be limited in order to prevent undue effect. Any normal fertilizer
program involving the use of not more than about 80 to 100 pounds of nitrogen
per acre in a crop season should not cause undue loss unless the soil provides
large amounts of nitrogen. If a good muck soil is planted to gladiolus, it is
advisable to use no nitrogen in the fertilizer except under cold and wet condi-
Gladiolus plants, especially from planting stock and bulblets, have an im-
portant nitrogen requirement, and, in order to realize the best crop, adequate
nitrogen must be supplied. If heavy leaching losses occur, it is advisable to
repeat the application of fertilizer. When Fusarium is not a serious problem,
d'e to varietal resistance or clean bulbs and soil, the grower may fertilize
more liberally with nitrogen so long as he maintains the calcium and potassium
at a good level.
1. Bud rot. We have experimental evidence that physiological bud rot may be caused
by relatively low calcium content of the spikes. Preventive measures include (1)
adequate liming, (2) avoiding a nutritional imbalance due to excess magnesium, po-
tassiam, sodium, or nitrogen, (3) spraying with 4 pounds of calcium nitrate per
hundredd gallons of water two to four times between the stage spikes first begin to
slip and the time flower cutting starts, and (4) broadcasting 1000 pounds of gypsum
per acre before planting.
2. Topple of Gladiolus, the breaking over of spikes as they open in vases, is
caused by low calcium content of the spikes and may be largely prevented by the
methods used for bud-rot control above.
3. Iron Deficiency is identified by a yellowing of new leaves, especially the
fourth to seventh leaves. Spikes will also be yellow or pale green-;. 'If:the condi-
tion is severe, the first to the third leaf may also be affected. Iron deficiency
is found mostly on older soils that have a history of copper accumulation. Control
measures include adequate liming, to the pH range 6.0 to 6.5 before planting and
soil treatment with iron ethylene diamine tetracetic acid (iron EDTA) at the rate
of 20 pounds active ingredient per acre at the time the deficiency is found. This
material, with trade names of Sequestrene and Versene, should be worked into moist
soil. If severe iron deficiency is expected on the basis of the history of the
soil, it is well to include 20 to 30 pounds of iron EDTA per ton of fertilizer to
be used in all applications before flower harvest.
4. fCopper deficiency is encountered principally on new land. This deficiency is
identified by an abnormal wilting of leaves, especially noticeable in Valeria. Con-
trol methods involve broadcasting 20 to 40 pounds of copper sulfate per acre on new
land before planting. The heavier rates are to be used on soils with greater or-
ganic matter content. If the deficiency develops during the growing season, a
sicZdress fertilizer application supplying 10 pounds of copper sulfate per acre
shoJld be made.
5 B7ron deficiency is recognized by a characteristic notching on edges of leaves
anid by translucent streaks along the veins of Hopman's Glory variety. The deficien-
cy is more likely to occur in the one to three-leaf stage and may result from an
abnormally low boron reserve in the bulb. In addition to having 0.2 percent borax
in the fertilizer, the grower may spray with 1 1/2 pounds of borax in 100 gallons
of water 2 or 3 times if boron deficiency symptoms are found. It is reported, how-
ever, that spraying too frequently with borax may cause brittle spikes. Borax is
very easily leached from the soil which makes repeated applications of borated fer-
tilizer necessary. Less than about 15 ppm boron in recently matured gladiolus
leaves is an indication that boron may be a limiting factor.