Title: Gardenias in Florida
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Title: Gardenias in Florida
Series Title: Gardenias in Florida
Physical Description: Book
Creator: Conover, Charles Albert,
Publisher: Agricultural Extension Service, Institute of Food and Agricultural Sciences, University of Florida
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CIRCULAR 313


GARDENIAS


IN FLORIDA

CHARLES A. CONOVER
Assistant Ornamental Horticulturist
Agricultural Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville


The gardenia is a favorite land-
scape shrub throughout Florida,
since it is highly valued for scent-
ed white flowers borne above
glossy, dark green leaves (Figure
1).
Gardenias belong to the genus
Gardenia, a member of the Rubia-
ceae family, and is represented in
Florida primarily by two species:
Gardenia jasminoides containing
many varieties, and Gardenia
thunbergia, grown primarily as a
rootstock. Gardenia jasminoides is
native to China although most
named varieties have arisen in
cultivation, and Gardenia thun-
bergia is native to South Africa.
This latter species is valuable due
to its resistance to nematode at-
tack and vigor it imparts to
species grafted on its root.

LANDSCAPE USE
Gardenias are used primarily as
free-standing specimens, although
they can be used in shrubbery
borders and as foundation plants.


Use as a free-standing specimen
is recommended since gardenias
are easier to maintain when not
surrounded by other plant ma-
terials. Gardenias have a com-
paratively high maintenance re-
quirement due to attack by a
number of pests, and inclusion in
plantings with other plant ma-
terials increases the problem.
Gardenias should be planted in
full sun for best flower produc-
tion, or where broken, shifting
shade is present. Areas of heavy
shade should be avoided.

VARIETIES
In Florida, gardenia varieties
are available "own root," or graft-
ed on rootstock of Gardenia thun-
bergia. Grafted plants are usually
more vigorous and produce more
and larger flowers than "own root"
plants; however, plants grafted on
Gardenia thunbergia rootstock are
not completely winter-hardy north
of Tampa, Orlando and Cocoa.
Many varieties of Gardenia jas-
minoides can be grown in Florida.


APRIL 1967

























Figure I. Gardenia Jasminoides 'Veitchi'.


Most varieties have not been ob-
tained by breeding but have re-
sulted from mutation and therefore
can be increased only by vegeta-
tive propagation. There exists
considerable variation in flower
size and form, blooming time and
duration, and plant growth among
varieties. The following list con-
tains some varieties available in
Florida.
AMEII YOSHIOKA. Flowers
of this variety are outstanding,
measuring 4 to 5 inches in diam-
eter and having the desirable
camellia flower form. Foliage is
a brilliant dark green, and leaves
are rounded at the apex. It is a
vigorous grower and produces an


abundance
spring.


of flowers in late


AUGUST BEAUTY. Distinc-
tive due to its dark green, long
pointed leaves and late blooming
period. Flowering occurs sporadi-
cally during summer, but heaviest
bloom occurs in late August.
BELMONT.-This is a vigorous
grower with dark green foliage,
that produces large flowers (4 to
5 inches in diameter) throughout
much of the growing season.
CORAL GABLES. Produces
large flowers on compact plants.
Dark green, lustrous foliage, sub-
tends large, fragrant flowers which
bloom throughout summer months.





GLAZERI. Flower production
is heavy on this variety and foliage
is medium green color. Peak bloom
occurs in April in southern Florida
and in May and early June in
northern Florida.
HADLEY. Flowers are pro-
duced in early spring above glisten-
ing black-green foliage. A vigor-
ous grower with large flowers.
MIAMI SUPREME. Produces
large flowers (4 to 6 inches in
diameter) with desirable camellia
form above medium to dark green
foliage.
MYSTERY.-A compact, bushy
plant with glossy, dark green foli-
age. Large, fragrant flowers are
produced during summer months.
RADICANS. A miniature-size
gardenia with compact, spreading
growth habit. Small flowers are
produced profusely in early sum-
mer.
VEITCHI. A small-flowered,
dwarf gardenia, used extensively
in greenhouse pot production but
also very satisfactory in the gar-
den. Foliage is of a medium green
color and flowering occurs in early
spring.
VEITCHI everbloomingg form).
-Same as Veitchi in flower type
and growth habit, but some flow-
ers occur throughout the year.

PROPAGATION
Varieties of Gardenia jasmi-
noides grown in Florida are in-
creased by cuttings or grafting.
Production of plants for northern
Florida should be restricted to
"own root" since plants grafted on
rootstock of Gardenia thunbergia


are not hardy. Gardenias produc-
ed for southern sections of Florida
should be grafted, since plants
grafted onto Gardenia thunbergia
are superior to "own root" ones.
Cuttings can be taken any time
during the year, but best success
will be obtained during spring or
summer months. Tip or midsec-
tion cuttings with wood 6 to 8
weeks old should be cut 4 to 5
inches long with at least 2 or 3 sets
of leaves. Cuttings can be taken
at or between a node, as they will
root from the cut end. Removal of
leaves is unnecessary and unde-
sirable and results in a longer root-
ing period.
Rooting of cuttings is best ac-
complished under continuous or in-
termittent mist, or in a closed case
propagating device. Rooting media
should be composed of clean, sharp,
builders' sand; peat moss; or a com-
bination of peat moss and perlite
in a 50-50 combination by volume.
Additional information on propa-
gation of cuttings can be found in
Agricultural Extension Circular
128, "Home Propagating Units."
Propagation should be by graft-
ing in southern Florida. For this
practice, a scion from a desired
variety is grafted to a seedling
rootstock of Gardenia thunbergia.
Rootstock seedlings are difficult to
obtain, but can be grown from seed
obtained from local sources. Ripen-'
ed seeds can be germinated in flats
or pots in a mixture of peat moss
and perlite or peat moss and sand.
Seed germinate slowly and errati-
cally and seedlings should be re-
moved from the germinating
device as soon as they germinate
and form their first true leaves.
When seedling rootstocks are pen-





cil thickness in size they are ready
to be grafted.
Types of grafts most successful
for joining gardenias are the
splice-graft and saddle-graft (Fig-
ure 2). The entire rootstock top is
removed with a long, sloping cut
for the splice-graft. A scion is then
selected from a desired gardenia
variety that has a diameter similar
to the rootstock and is cut with
a similar sloping cut. Scion and
rootstock are joined so cambium
layers meet, or are closely aligned
on both or at least one side. They
should then be bound together
with a rubber budding strip and
waxed or wrapped with a plastic


SPLICE GRAFT
Figure 2.


tie strip. In either case, the joined
area should be completely covered
to prevent dessication and entry
of water which might prevent
proper callusing of the cambial lay-
ers. The inverted saddle-graft is
usually preferred because it is easy
to make and stronger than the
splice-graft. To make the saddle-
graft, the top must be removed
from the rootstock with a horizon-
tal cut at a point where stem diam-
eter is equal to or slightly less than
that of a pencil. The rootstock
top is then split for a distance of
1/2 inch. The scion selected from a
desirable variety should have a
similar or nearly similar diameter.





























AVERTED SADDLE
GRAFT





The scion base should be cut in the
shape of a wedge, inserted into the
split top of the rootstock and cam-
bial layers aligned. The joined area
is then treated as mentioned for
the splice-graft above.
The plant should be placed in a
shaded spot after a graft is made
and the humidity maintained as
nearly as possible at 100 percent
to prevent wilting of the scion.
Some growers mist plants through-
out the day to prevent wilting, or
plants may be placed inside a plas-
tic enclosure in a shaded area
to maintain necessary humidity.
Grafts should begin to callus with-
in 2 weeks and be self-supporting
within a month.

SOIL REQUIREMENTS
Gardenias grow under a variety
of soil conditions but they do best
in a well-drained soil high in
organic matter. Soil pH is im-
portant since it affects availability
of mineral elements and should be
maintained near 6.0. Soil pH should
be lowered if plants are to be grown
in an area where the soil is alka-
line (pH 7.0 or above). Soil pH
can be lowered by addition of sul-
fur. One pound of sulfur per 100
square feet will lower pH one unit
on mineral soils, whereas high
organic soils require 2 pounds per
100 square feet. Do not use more
than 1 to 11/ pounds of sulfur per
100 square feet per application or
more often than once every 6
weeks.
If the soil does not naturally
contain a high level of organic
matter it should be supplied in
the form of peat moss, compost
or leafmold. Usually addition of
2 inches of either of these ma-


trials to the soil surface, and
thorough incorporation to a depth
of 6 to 8 inches is satisfactory.
Addition of organic soil amend-
ments increases water-holding and
nutrient-retaining capabilities of
sandy soils.

FERTILIZATION
Proper fertilization of gardenias
is important to growth and flower
production. Good results can be
obtained if gardenias are fertilized
4 times a year winter, spring,
summer and fall. Acid-forming
fertilizers containing 6 to 8 per-
cent nitrogen, 4 to 8 percent phos-
phorus and 4 to 8 percent potas-
sium such as 6-6-6, 8-8-8 or 8-4-8
are recommended. Organic ferti-
lizers are not necessary to good
gardenia growth and are more ex-
pensive than chemical fertilizers,
but they can be used if preferred
to chemical forms. Frequently
plants will become chlorotic due to
a deficiency of one or more minor
elements which can be corrected by
soil or foliage application of the
missing elements. Most frequently
the cause of chlorosis in gardenia
is due to lack of iron, usually re-
sulting from a high soil pH, which
can be corrected by lowering pH
as listed under soil requirements.
Iron chelates, or iron sulphate are
recommended sources of iron and
can be applied to the soil or spray-
ed on foliage. Follow manufactur-
ers recommendations for iron
chelates, or apply iron sulphate in
a 1/4 to 1/2 percent solution. Foliar
applications of iron should be made
where a high soil pH cannot be
lowered. Some homeowners prefer
to use fertilizers containing minor
elements each time they fertilize,





but this is not the best policy,
since these elements can become
toxic to gardenias at relatively low
concentrations on some soils. How-
ever, such fertilizers can be used
to advantage twice a year.

GENERAL CARE
Pruning is necessary to keep
plants shapely and in scale with
the landscape. Pruning should be
done just after the plant has com-
pleted its flush of bloom. Pruning
after October 1st will decrease the
number of blooms that will be ob-
tained the following year.
Research in Florida indicates
that buds on gardenias are initiat-
ed and developed by a combination
of short daylengths (long nights),
low temperature and wood of the
proper age. Pruning should be
made early enough to allow new
growth to be at least 4 to 6 inches
long before October 1st.
Watering is important to flower
production since it largely controls
number of flower buds that will re-
main on a plant to maturity. If
water stress occurs in a heavily
budded plant a large number of
buds will fall before they open.
Therefore, soil should be kept moist
while the plant is in bud, and large
variations in soil moisture should
be avoided.

BUD DROP
Premature flower bud drop of
gardenias often plagues home
gardeners and is frequently caused
by root injury. However, other
factors controlling bud drop include
nutrition, insect injury and climat-
ic conditions.
Root Injury.-may occur as a


result of nematode infestations,
poor watering practices, poorly
drained soils, excessive fertilization
and mechanical injury.
(1) An excessive number of
nematodes in the soil will often
damage roots and prevent normal
uptake of water and nutrients.
(Control methods are listed under
"nematodes".)
(2) Poorly drained, wet soils,
or excessive watering, will cause
root injury to gardenia due to ex-
clusion of oxygen.
(3) Application of excessive
amounts of fertilizer can cause de-
hydration of root systems due to
excessive soluble salts, thus it is
important to follow fertilizer rec-
ommendations.
(4) Mechanical injury to root
systems occurs most often during
transplanting, and care must be
taken to prevent as much damage
as possible. Gardenias should al-
ways be planted at the same depth
as they grew in the nursery, and
transplanting while plants are in
bud is not recommended unless
buds are considered unimportant.
Insects.-can damage unopened
flower buds and cause them to
drop. Thrips and aphids are most
troublesome. Aphids can usually
be seen, but thrips are very small
and can go undetected until con-
siderable damage has occurred. In-
secticides are listed in the insect
pest section.
Climatic Conditions. During ex-
cessively hot, dry weather the pos-
sibility of flower bud drop is
prevalent since the plant is unable
to absorb water rapidly enough
to compensate for water loss
through transpiration. Mainten-
ance of adequate soil moisture and





frequent light syringing will aid in
reducing water loss and bud drop
under such conditions.

NEMATODES
Nematodes are among the most
serious pests of gardenias in Flor-
ida. They are microscopic, para-
sitic round worms that feed on
gardenia roots. At least one spe-
cies of nematode causes galls on
roots, but others cause injury not
as easily seen. Injury by nema-
todes may cause dwarfing and un-
thrifty growth which may eventu-
ally result in plant death. Another
symptom resulting from nematode
injury is chlorotic foliage, indicat-
ing an iron deficiency. This may
occur due to roots being damaged
by feeding nematodes, which pre-
vents them from taking iron from
soil in proper amounts.
In southern Florida gardenias
are usually grafted on Gardenia
thunbergia rootstock, which resists
nematode attack, and therefore
nematodes are not a serious prob-
lem when this rootstock can be
used. Some gardenias are sold in
southern Florida which are not
grafted to this rootstock, and gar-
denias in northern Florida cannot
be grafted due to possible cold
damage. Nematodes can be con-
trolled by soil fumigation with
methyl bromide gas prior to plant-
ing, or around established plants
with DBPC (Nemagon or Fuma-
zone). Methyl bromide gas should
be applied at the rate of 2 to 3
pounds per 100 square feet under
an air-tight plastic covering which
can be removed after 24 hours.
The soil is then allowed to aerate
for another 2 or 3 days before
planting. DBPC is applied at the


rate of 11/4 pounds of 17.3 percent
granules or 4 tablespoons of 50 per-
cent emulsifiable concentrate per
100 square feet. Granular ma-
terials can be applied directly to
soil, but emulsifiable materials
should be mixed with water. Both
materials can be applied before or
after planting and once each year
during March or April, if neces-
sary.

DISEASES
Probably the most serious
disease of gardenia is stem canker,
which occurs on the main stem at
the soil line. However, this disease
is not too common in Florida. This
disease can be distinguished by
roughened, cracked areas near the
soil line, which form a cankerous
growth. The disease organism en-
ters the plant through wounds, so
every precaution should be taken
to prevent damage to stems. Once
a plant is infected it should be de-
stroyed to prevent infection of
other plants. No fungicide present-
ly on the market will control the
disease once it has entered the
plant. Therefore, whenever a plant
is wounded it should be painted
with a wound dressing containing
a fungicide.
Two or three leaf-spotting dis-
eases may sometimes attack gar-
denias, but these can be controlled
with Dithane M-45 (Fore), Zineb
or Captan. Use 2 tablespoons
Dithane M-45, 80 percent WP,
Zineb 75 percent WP or Captan
50 percent WP per gallon of water
and spray foliage to run-off.
A disease called "sooty mold"
often occurs on the foliage causing
it to turn black. Foliage is not
injured by this organism, but it





does prevent sunlight from reach-
ing the leaf and thereby reduces
photosynthesis. The organism is
not parasitic but lives on honey-
dew secreted by whiteflies. Sooty
mold can be controlled best by
controlling whiteflies, but it can
be sprayed with a fungicide after
controlling flies to achieve more
rapid control.

INSECT PESTS
Many insect pests attack gar-
denias in Florida and can be
troublesome if proper control meth-
ods are not followed. The most
injurious insects include scales,
aphids, spider mites, thrips and
whiteflies.
Scale insects attacking gardenias
include cottony cushion, Florida
wax, soft brown scale and others.
These insects attach themselves to
host plants after hatching and give
stems and/or leaves a lumpy ap-
pearance. Scale insects are difficult
to control, especially as they be-
come older. Malathion, Dimethoate
(Cygon) and oil emulsion sprays
are all effective in controlling scale.
Use 2 to 3 tablespoons Malathion 50
to 57 percent or 1 teaspoon of
Cygon 43 percent emulsifiable con-
centrate per gallon of water. The


spray should be applied a second
time in 2 to 3 weeks following ini-
tial application to achieve effective
control. Oil emulsion sprays are
effective in controlling scale, but
can be used only when tempera-
tures average between 40 and 85
degrees F., as plant injury may oc-
cur at lower or higher tempera-
tures.
Aphids, thrips and whiteflies can
be controlled with Malathion and
Cygon, as recommended for scale
control. One application usually
will be sufficient to achieve con-
trol.
Spider mites can cause consider-
able damage to gardenias especially
during hot, dry periods of the year.
These insects are small and feed
primarily on the under side of the
foliage; therefore, considerable
injury usually has occurred by the
time the homeowner notices the
small, colorless or whitish spots
in the leaves, caused by their feed-
ing. Spider mites can be controlled
with Kelthane or Aramite, and best
control will be obtained if sprays
are applied before the population
becomes too large. Aramite 15
percent WP or Kelthane 181/2 per-
cent WP should be applied at the
rate of 1 to I1/. tablespoons per
gallon of water.


COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
and United States Department of Agriculture, Cooperating
M. O. Watkins, Director




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