Acclimatization of Ficus benjamin: A Review P 3
q/-5 SEP 301994
q1- K. Steinkamp', C.A. Conover and R.T. Pooleniers f lorida
University of Florida
Central Florida Research and Education Center Apopka
CFREC-A Research Report RH-91-5
The most widely utilized tropical tree in the interiorscape industry is Ficus benjamin or
weeping fig, a member of the family Moraceae and indigenous to southeast Asia. Ficus
benjamin and its cultivars have been the focus of much of the foliage plant acclimatization
research for the past 20 years because of their enormous popularity with the plant buying public
and also because weeping figs are among the sun-shade plants most clearly benefiting from the
Properly acclimatized weeping figs can make the transition from production to the
interior environment when given proper fertilization and irrigation corresponding to available
light levels. Non-acclimatized plants defoliate, and may die if leaf drop is severe. The extent
of plant quality lost is dependent on a host of factors encountered during production, shipping
Early Ficus benjamin acclimatization studies were aimed at converting trees grown in
full sun to shade plants able to adjust to low light interiors. Conklin (10) developed a system
of "pre-acclimatizing" plants being grown for interior use when he found that plants placed in
heavily shaded greenhouses and watered sparingly for 2 months prior to placement in interior
settings consistently scored higher quality grades than plants not receiving the shade treatment.
In 1973 Conover and Poole (11) determined that lowering light levels from a maximum of
12,000 ft-c utilized during production to 2,500 ft-c for just 12 weeks lessened leaf abscision on
weeping figs subsequently placed in simulated interior environments having a light intensity of
50 ft-c 8 hours per day for ten weeks. Two years later, Conover and Poole (12) showed that
containerized Ficus benjamin received higher plant grades, and dropped fewer leaves after 10
weeks in an interior setting if they were first acclimatized for at least 5 weeks under 1,250 to
2,500 ft-c (60% to 80% shade). Longer periods of shading supplied better quality plants. Plants
also retained more leaves as interior light supplied 12 hours per day increased from 250 to 750
2Professor and Center Director, and Professor of Plant Physiology respectively, Central
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to 1250 ft-c. Light compensation point (LCP) is that point at which carbohydrates required by
plants in respiration are equal to carbohydrates produced by photosynthesis. Photosynthetic rate
must equal respiration rate if the plant is to survive. Plants with lower LCPs adapt better to low
light interior environments. Joiner, Conover and Poole (25) found that Ficus benjamin LCP
can be controlled by light levels utilized during production. High quality acclimatized plants
were grown under shade in less time than the previously accepted acclimatization method of
growing plants under full sun before subjecting them to an acclimatization period under low
light. Conover and Poole (13, 14) reported that tree height, quality and foliage color increased
when production shade levels were increased. Only trees grown under 80% shade continued to
grow after 6 months in a simulated interior setting. Trees grown under shade, however, did not
develop thick trunks necessary to support large specimen trees.
Turner, Reed and Morgan (40) compared two acclimatization methods at 5 light
intensities to compare effectiveness in reducing leaf drop after placement indoors. The two
methods tested were 1) production under 0, 20, 40, 60 and 80% shade levels prior to placement
indoors, and 2) production in full sun followed by an 8 week acclimatization period under 20-
80% post-production shade levels, then placement indoors. Plants grown in full sun dropped
the most leaves indoors. As production or post-production shade level increased, defoliation
decreased. Plants grown under the 80% shade treatment dropped the lowest number of leaves.
Ficus benjamin grown in full sun develop thicker trunk diameters than shade grown
trees. Conover and Poole (16) found wind movement in shaded production areas produced some
thickening of trunks but not enough to support large specimen trees. Eight weeks of full sun
followed by 16 weeks of 63% shade produced plants with thicker trunks but otherwise of the
same quality as those grown in shade for the entire 24 weeks. Most Ficus benjamin grown
today are acclimatized during production under shade, the exception being large specimen trees
requiring thick trunks.
Although these experiments proved that production and post-production acclimatization
procedures result in greater leaf retention and increased plant longevity indoors, research
explaining the physiological changes taking place in leaves in response to environmental changes
were needed to help develop optimum production regimes.
Many researchers have examined LCPs of shade and sun grown plants and concluded
shade grown plants had lower LCPs than sun grown plants. New changes in leaf structure in
response to production light levels were examined to help explain the shift in LCP. Peterson
et al. (30) found that trees grown under high light intensities had smaller thicker leaves with two
distinct palisade layers, while shade grown leaves had only one palisade layer. Fails, Lewis and
Barden (18, 19, 20) studied the anatomy and morphology of sun and shade grown foliage and
confirmed these findings. They also reported greater stomatal density in sun grown leaves,
although shade grown leaves had more stomata per leaf. Sun grown leaves were small and thick
with 2 layers of elongated palisade mesophyll cells and chloroplasts were aligned along the radial
uec larger man in sun grown plants. wnen net pnotosyninesis or plants grown in run sun ana
50% sun was compared under various photosynthetically active radiation (PAR), shade grown
leaves had a photosynthetic advantage over sun grown leaves at PAR comparable to lighting
found in interiors. Sun grown leaves also transpired more at all PAR levels tested.
Light and Fertility
Light and fertilizer significantly affected LCP in Ficus benjamin in a 3 x 4 factorial
experiment that tested plants grown under 0, 30, 55 and 80% shade fertilized with 700, 1400
or 2100 lb N+K/A/yr (6). Increasing shade levels decreased LCP at each shade level tested.
Increasing fertilizer rates increased LCP, although fertilizer was less effective than shade level
in altering LCP. Plants grown in full sun with 700 lb N+K/A/yr had LCPs nearly 3 times
higher than the plants grown under 80% shade and 700 lb N+K/A/yr.
Research by Ceulemans, Gabriels and Impens (5) has shown that fertilization level during
reductionn influences plant morphology and structure. Johnson et al. (22) discovered that Ficus
benjamina receiving higher nitrogen (N) rates had less leaves in the upper half of sun or shade
grown plants Increased N levels increased LCP of sun grown plants but reduced LCP of plants
grown under 47% light exclusion. Higher N fertilization increased leaf development in lower
md mid plant portions of the tree which increased LCP and potential leaf drop on plants grown
.n full sun. Shade grown plants had reduced LCPs, lower carbohydrate levels in leaves and
roots, more leaf chlorophyll, were of higher quality and had longer post-harvest life than sun
grown plants. Milks et al. (28) found sun grown plants had twenty-seven percent more leaf
carbohydrate than those grown under 65 % light exclusion (4180 ft-c), so reduction of LCP with
increased N could be an interaction of N and low reserve carbohydrate level. Increased
)otassium (K) allowed more carbohydrate translocation to the root system.
Joiner, Johnson and Krantz (27) in testing 2 light levels, 3 N and 3 K levels on LCP,
,hoot and root growth, canopy distribution and leaf tissue nutrient content of Ficus benjamin
foundd that plants grown under 47% shade for 7 months had significantly lower LPCs than plants
producedd under full sun. N level slightly affected compensation point but K level had no effect.
Higher N levels increased shoot growth and shade grown plants receiving high N levels had a
higher shoot/root ratio. Light level did not affect amount of carbohydrates in the leaves but sun
grown plants had more root carbohydrates. Root carbohydrate levels also increased when K
evels were increased.
Johnson et al. (24) found that leaf diffusive resistances of Ficus benjamin grown in full
sun were lower than those from 47% light exclusion partially explaining why sun grown plants
ieed more water than shade grown plants. Fifty-three percent more stomata were found in sun
eaves. High KCl increased transpiration rates, and foliar levels of K were higher in sun grown
plants but unaffected in shade plants. Acclimatization also affected respiration rate and as a
plant became fully acclimatized respiration rate declined dramatically which reduced
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requirements and practices in growing Ficus benjamin.
Plants can lose leaves during shipping and storage due to water stress because of limited
growing medium volume. Irrigation frequency during production affected leaf drop where
acclimatized plants were placed indoors. Johnson, Ingram and Barrett (21) reported that plant,
watered at 3 day intervals during production dropped fewer leaves when moved to simulatec
interior environments than plants watered at 6 and 9 day intervals. However, results of research
by Peterson, Sacalis and Durkin (31, 32), while showing that water stress is a contributing factor
in leaf abscission, suggested that preconditioningg" by exposing plants to water stress would no
be economically feasible because growth rates of Ficus were dramatically reduced by watei
stress during production and leaf abscission was not appreciably reduced when plants were late
subjected to severe water deficits. Ficus benjamin could not be "pre-conditioned" to lessen leal
drop in times of severe water stress.
Ficus benjamin sometimes experience substantial leaf drop during shipping and dark
storage. Researchers in the late 70's and early 80's turned their attention to procedures tc
determine the effects of shipping and storage environments on acclimatized weeping figs. Poolc
and Conover (36, 37) found that quality of Ficus benjamin grown under 63 % shade was much
better than quality of plants grown under full sun or 30% shade when test plants were placed
in interior environments for 12 weeks following a period of 0, 5, 10, or 15 days of storage ir
complete darkness at 60-65 F and 65+ 5% relative humidity. The plants receiving higher
fertilizer and light levels during production had more leaf abscission during simulated shipping
and later in the interior environment. Longer storage time also increased amount of leaf drop.
Researchers found that storage duration and temperature also affected the quality of Ficw
benjamin. Collins and Blessington (8) dark-stored Ficus benjamin for 4, 8, or 12 days at 370,
450, 700, 95 or 102F then placed plants in interiors for 30 days. Plants were not damage
when stored at 700F or 95F or when stored for 4 days. Leaf loss and foliar damage were mort
severe as dark storage time increased from 4 to 12 days. After subjecting large Ficus to storage
periods of various temperatures, Poole and Conover (38) found that specimen trees having ovei
300 leaves and held at 50F had the highest plant grade (4.2 based on a quality scale of 1 =
poor, unsalable, 3 = fair, salable, 5 = excellent quality) 12 weeks after removal from storage.
Plants shipped at 660F, the temperature closest to the most commonly used shipping
temperature, received a lower plant grade of 3.0. Buck and Blessington (3, 4) held Ficus ai
40, 700 or 98F for 3, 6 or 9 days. Plants were adversely affected during simulated shipping
by 40 and 98F, with leaf loss increasing with exposure time. Foliar damage was severe witt
plant grade the lowest for weeping figs exposed to 980F for 6 or 9 days. Plants held at 701
showed no foliar damage and only slight loss in quality regardless of shipping duration. Aftei
8 weeks in a simulated interior environment plants held at 40 and 980F during simulated
shipping had not recovered lost quality and showed even more severe foliar damage and greater
leaf loss. Chlorophyll content of leaves decreased as storage temperatures increased.
Some foliage plant producers spray plants with foliage shine materials prior to shipment.
oiner, Conover and Poole (26) found that leaf shine compounds applied to Ficus benjamin
)rior to storage raised the LCP reducing tolerance to low light stress. Treated plants lost about
3 times more leaves compared to untreated plants within 2 weeks of leaf shine application
indicating treated plants need higher interior light levels to maintain the same quality as untreated
Foliage plants could be subjected to water stress during long-term transit, which can
contributee to leaf abscission. Peterson and Blessington (34) applied Wilt-Pruf (Nursery Specialty
'o., Greenwich CT) to Ficus benjamin foliage prior to storage to evaluate the influence of an
Lntitranspirant on plant quality during dark storage. Wilt-Pruf increased leaf drop after dark
storage treatments and plants were not salable two weeks after being dark stored for 8 and 12
lays. Chlorophyll content of leaves decreased after 4, 8 and 12 days of storage.
Foliage plants often develop etiolated or spindly new growth when subjected to extended
)eriods of low light levels such as those encountered during shipping, dark storage, display in
etail shops and in dimly lit interiors. Peterson and Blessington (35) treated Ficus benjamin
vith the growth regulator ancymidol [ao-cyclopropyl-a-(p-methoxyphenyl)-5-pyrimidinemethanol]
o evaluate its potential for controlling undesirable postharvest internode elongation and
increasing Ficus postharvest keeping quality during dark storage and under incandescent (INC)
nd Cool White fluorescent (CWF) lights indoors. Plants were treated with ancymidol as a soil
trench using 1.0 mg/15 cm (6 inch) pot using a standard volume of 200 ml (7 oz.)/pot two
months after potting. All ancymidol treated plants also received a 200 ppm spray two months
afterr the soil drench treatment. Plants were dark stored for 4, 8 and 12 days in shipping boxes
before being held 4 months in an interior environment under 110 ft-c. Ancymidol treated plants
Dropped fewer leaves compared to untreated plants during all dark storage times tested. Treated
plants also received higher plant grades than untreated plants for all dark storage times tested
afterr plants were held under both lamp sources in interior environments for 4 months. Ficus
inder INC lamps lost the fewest number of leaves and scored the highest quality grades.
Johnson, McConnell and Joiner (23) treated weeping figs to the growth regulator
thephon at rates of 500 and 1000 mg (active ingredient) /25 cm (10 inch) pot applied as a soil
Irench, to determine effects of ethephon on growth responses, carbohydrate content, anatomical
changess and leaf drop of plants grown under full sun and 47% sun exclusion. Treated sun and
hade grown plants developed a prostrate growth habit and set fruit. Leaves of sun plants had
* mesophyll with multiple palisade layers, while shade plants had only limited regions of
multiple cells. Ethephon treatments reduced intercellular spaces in palisade and spongy
nesophyll cells, especially near leaf margins. High shoot/root ratios, reduced leaf area and
leavy leaf drop during 3 months in an interior environment occurred with ethephon treatment,
vith nlant ironwn in full viin affeprcte monre than hadrle. rnmwn nlnnt-
Barrett and Nell (1) reported no increase in leaf drop after limited observation of plants
placed in interior environments after treatment with the growth retardants ancymidol [ca-
cyclopropyl-a- (p-methoxyphenyl)-5-pyrimidinemethanol], paclobutrazol [l-(4-chlorophenyl)-4,
4-dimethyl-2-(1,2,4-triazol-l-yl)] and EL-500 [oa-(l-methylethyl)-a-(4-(trifluoromethoxy)
phenyl)-5-prymidinemethanol], although these experiments primarily focused on the three growth
regulators abilities to limit intermodal length during production. More research examining
various growth regulators ability to control growth of Ficus benjamin in interior environments
In recent years, interiorscapers have become concerned about the possible side effects
of continuous 24 hour lighting on their plantings in airports, shopping malls and other areas.
Questions have been raised about the effects different kinds of artificial light sources have on
plants and which if any is superior. Collins and Blessington (9) grew Ficus benjamin under
3000 or 6000 ft-c for 5 months then held plants indoors for 12 weeks under INC or CWF lights
at light intensities of 75 or 150 ft-c PAR for 12 hours a day. Chlorophyll content was greater
in plants grown under 3000 ft-c and plants dropped fewer leaves when held under 150 ft-c.
Collins and Blessington (7) also examined the effects of dark storage, light source and
light duration in an interior environment on the postharvest keeping quality of Ficus benjamin.
Ficus benjamin was stored in the dark for 0, 3, 6, 9 or 12 days then held in an interior
environment for 12 weeks under 6, 12 or 24 hours of light per day from either INC or CWF
lamps at 149 ft-c PAR. Plants stored for shorter periods lost fewer leaves and received higher
plant quality grades. Plants lighted for 24 hours per day had less leaf drop and better plant
grade than those from shorter light periods. Chlorophyll content of leaves increased as light
duration increased for plants held under the CWF lamps. Plants lighted for 6 hours per day
under INC lamps had the lowest chlorophyll content after 12 weeks indoors.
Conover, Poole and Nell (17) grew Ficus benjamin for 1 year under 100 or 200 ft-c
from CWF lamps for 12, 18 or 24 hours per day. Plants produced with the continuous 24 hour
lighting had the lowest quality scores and more chlorosis than plants exposed to 12 to 18 hour
days. After one year the best plants were produced under 200 ft-c for 12 or 18 hours per day.
These two experiments suggest that continuous 24 hour lighting after dark storage or shipping
might be beneficial for a limited amount of time but becomes detrimental after extended periods.
Turner, Morgan and Reed (41) grew Ficus benjamin under the following light regimes
for 1 year 1) 100% PAR from fluorescent, 2) 70% PAR from fluorescent plus 30% from
incandescent, and 3) 50% each from Gro-Lux and Gro-Lux Wide Spectrum fluorescent. All
light intensities were standardized at a total of 150 ft-c for 4 months then 100 ft-c for 8 months.
No light source was proved superior for maintenance of the plants for 1 year indoors. In a
second experiment three fertilizers were tested on plants receiving 150 ft-c for 3 months then
90 ft-c for 9 months. Fertilizers tested were: 1) soluble fertilizer (Peter's 20-20-20, Peters
TIA;- ^-... 7 % IA 1on 11L- --
200 ppm N:88 ppm P:166 ppm K; 2) slow-release fertilizer (Osmocote 14-14-14, 3 month
release, Grace-Sierra Co., Milpitas, CA 95035) applied as a top dress every three months at 4.1
g/6 inch pot (0.57 g N:0.25 g P:0.47 g K); and 3) an unfertilized control. At the end of one
year the effects of fertilizer treatment were found to be minimal. These results agree with
research by Conover and Poole (15) who also found few differences between slow-release and
liquid fertilization at low light intensities during a 12 month study. Conover et al.(17) found
an increase in chlorophyll content of leaves with an increase in slow-release fertilizer rate, but
only a limited increase in plant quality after one year in the interior.
In the past few years some research has focused on genotype selection as a means to
minimize leaf drop and enhance postharvest keeping quality of Ficus benjamin. Scientists
wanted to know how much of the physiological, anatomical and morphological traits of Ficus
induced by environmental factors were determined genetically. Steintz, Ben-Jaacov and Hagiladi
(39) determined that cultivar differences in Ficus benjamin were a major factor affecting leaf
drop during shipping, dark storage and subsequent performance in interior environments. In
another experiment Ben-Jaacov, Ziv and Steinitz (2) grew three clones of Ficus benjamin with
similar morphology under 3 light intensities and variations in the morphological development of
the clones in response to light intensity were recorded. Plants were dark stored for 2 weeks,
then placed in an interior environment or placed directly into the interior setting without
undergoing the dark storage phase. The length of dark storage promoted leaf abscission and the
response pattern to light intensity during production, with regard to leaf drop during simulated
interior conditions, showed a clear clone-dependent specificity.
Ottosen and Hoyer (29) reported up to 42 % difference in leaf abscission of some selected
fast growing clones of Ficus benjamin after simulated shipping of pot plants in darkness
followed by low light conditions in a simulated interior environment. The clones that grew
faster under low interior light also had superior keeping quality indoors. This research suggests
the possibility of selecting genotypes capable of fast growth and good keeping quality under
interior conditions through plant breeding programs.
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Proc. Fla. State Hort. Soc. 96:264-265.
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intensity during growth and to subsequent dark storage of Ficus benjamin and Ficus
retusa HortScience 20(5):934-936.
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