.0A/L- Light and Fertilizer Recommendations for the Interior, C c
./c Maintenance of Acclimatized Foliage Plants "
C.A. Conover, R.T. Poole and R.W. Henle 994
University of Florida, IFA Florida
Central Florida Research and Education Center Apopka
CFREC-A Research Report RH-91-7
Previous research determined that many species of foliage plants, when produced under
lower light and fertilizer levels than species grown in full sun, produced a final product more
able to withstand interior environments. Progressive foliage plant producers eagerly adopted the
new production methods and called these plants "acclimatized". A larger, more diverse foliage
plant market now exists because most of the environmental plant industry has implemented
production regimes that produce acclimatized plants.
Indoor plants can be divided into three groups according to their physiological responses
to light. The first group includes extreme shade plants such as Aglaonema, Maranta and
Spathiphyllwn. These plants usually do well in all except the brightest of interior locations, but
do look best when placed in light levels of at least 75 ft-c minimum (Table 1). The second
group are termed sun-shade because these plants can adapt to a wide range of interior light
levels. Brassaia, Chamaedorea, Dracaena and Ficus are examples of sun-shade plants. The
third group of plants, high light flowering plants, termed full-sun plants, require such high light
intensities that they can not be adapted for long term indoor use. While some full-sun plants,
like chrysanthemums, may be used in interior locations to provide a temporary splash of color,
they will not continue to grow and bloom indoors and must be replaced periodically.
The two most important factors influencing foliage plant longevity in interiorscapes are
light levels and fertilizer application rates. These two factors are closely associated because light
level determines the rate at which plants use fertilizer. Various characteristics of the potting
medium also affect the rate at which nutrients are made available to foliage plants.
Light intensity and duration are most commonly the limiting factors when maintaining
plants indoors. Plants must receive a light intensity slightly higher than the intensity at which
it reaches its compensation point in order to survive. The compensation point is the point at
which a plant uses as much food as it produces. A plant's compensation point is influenced by
'Professor and Center Director, Professor, Plant Physiology and Professor, Environmental
Horticulture, respectively, Central Florida Research and Education Center-Apopka, 2807 Binion
Road, Apopka, FL 32703.
compensauon point oo mgn iur survival maoors, wnere iignt levels are mucn lower. However,
the compensation point can be adjusted gradually when plants are moved to less light, if the
difference in light levels is not too drastic. When this happens, foliage plants usually drop
leaves to conserve food, with the amount of foliage loss dependant on the degree of light
reduction. Production regimes producing acclimatized plants capable of adjusting to interiors
with minimal leaf drop has become standard in the environmental plant industry. Plants with
many small leaves having a compact growth habit were grown under higher light levels than
plants of the same species having a more open canopy with fewer, but larger, dark green leaves
and a less compact growth habit.
Light intensity depends on: 1) the light source, natural, artificial or a combination of the
two, 2) obstructions, natural and man made and 3) the amount of reflection from design
elements. A locations' light intensity is determined by averaging readings taken at plant height
between the hours of 11:00 a.m. and 1:00 p.m. on several days (during both cloudy and sunny
Light duration refers to the amount of time during a 24 hour period that plants are
exposed to light. Duration is critical because a longer exposure can compensate for
unsatisfactory light intensities. When intensity is inadequate, increasing light duration will help
plants adjust; conversely, when intensity is too high, a shorter exposure time may solve lighting
problems. Research has shown that plants maintained indoors grew better when they received
between 12 and 18 hours of light daily, while continuous 24 hour lighting was detrimental to
some species. Light intensity and duration are the two primary factors affecting indoor plant
survival and should be carefully determined before foliage plants are purchased and installed.
Only plants able to survive in the existing light conditions should be considered suitable for that
When repotting foliage, interiorscapers can be confused by. the wide selection of
prepackaged growing media on the market as well as the range of raw materials available to
create individual growing mixtures. Fertilizer levels in Table 1 are based on utilization of
potting media composed primarily of organic components with a high cation exchange capacity.
The cation exchange capacity of a medium determines its nutrient retention capabilities. Most
Drevackaged mixes contain mainly organic materials. Pottine media composed of large amounts
:e availability of most microelements. Most foliage plants grow best when the pH
um is between 5.0 and 6.5 and most commercially produced potting mixes are within
Low pH levels in potting media can be adjusted upward by addition of liming material
such as dolomite or calcium carbonate. High pH levels can be lowered by addition of sulfur.
The amount of liming material or sulfur needed to obtain a desired pH depends on the type of
organic material present in the medium and the original pH. Small amounts of lime or sulfur
will change pH of sandy potting mixes because of their lower cation exchange capacities. Mixes
primarily made up of peat moss have higher cation exchange capacities and require large
amounts of liming materials or sulfur to adjust pH.
Adjustment of pH levels should be made prior to repotting plant material since changing
the pH is more difficult once plants are growing in the medium. When plants do not need
repotting but require pH adjustments, the best material to raise pH is calcium hydroxide
(hydrated lime), 1 lb/100 gallon. Plants can be retreated every 4 weeks until desired pH is
obtained. Calcium carbonate applied to the medium surface will also raise pH.
When pH is too high, sulfur can be applied at a rate of 1 lb/100 ft2 to lower pH. Sulfur
may be applied once every 4 weeks until the desired pH level is obtained. Do not apply liming
material or sulfur more often than once every 4 weeks. Irrigation after application of liming
materials or sulfur application will remove residues from foliage if present.
In addition to raising pH, dolomite also provides the essential elements calcium and
magnesium. The addition of sulfur to lower the pH will provide that essential element. If these
elements have not been added to the media during the manufacturing process or while adjusting
the pH, they need to be added by some other means to ensure proper plant growth.
Soluble salts levels of the growing medium should be determined prior to utilization.
Many interiorscapes were not designed to accommodate large amounts of leachate, therefore
plants must be watered carefully so that minimal leaching occurs. When media have high
soluble salts concentrations, they should be heavily leached to remove excess salts prior to
utilization. The addition of unnecessary fertilizer ions into the medium can be avoided by
careful monitoring of fertilizer programs and plant damage can be reduced by using less
The recommended interior fertilizer application rates for selected foliage plants are listed
in Table 1. Application rates are recommended for four light intensities because plant's
nutritional requirements change with a change in light intensity When lHoht lrealcnp nrp vr l~mu
ig the greatly divergent light levels in which the various pl
this causes the plants in the lower light levels to be danu
no in the prnwincP meniium while nlante in the hichect lirht level!
nts are maintain
ged by excess s
: Trndrie nan l wu
e grow causeO Dy unaer remruzation.
nperature, watering frequency and the amount of water applied pei
nts originated in the tropics and therefore grow very slowly when
levels listed in Table 1 under these lower temp
alts to accumulate in the growing medium;
erature conditions could cause unu
therefnre~ nnnlicatinn rotec chnmilr
w-release fertilizers are temperature dependent. The specified release period, t
time fertilizer pellets actively release nutrients (the Osmocote listed in Table 4 l
7ciJUU u.L uiI, Yf.)Y, uJ uauaU U4a Vuu u1. ii Ia La
the manufacturer if the product is to be used i
i the product packaging and should be noted.
ilizer is released slows; as medium warms the
application rates can be manipulated by lengthen
placed in cool interiors and decreasing the time
I under warmer conditions.
e Amount of water annlied to the not at e Ph w:
-lAIIjJtaLU6I Wl I I. V A. UUL IL
_ -- f-
y uU Zct
release rate increases. Slow-release
ng the time between applications when
e between applications when foliage is
om me potting meaium ana mus arrests r
f the fertilizers listed in tables 2, 3 and 4
dium is thorouehlv saturated. but little or r
are for pi
Ir In pohina
are watered so that t
ilizer selection is ecc
_4._ MTyr "\ %mmrmi
omicallv important. Nitrogen is available from three nrimarv
0-50% nitrate nitrogen and the remainder came from ammonium oz
Uya, LCI1tULLI IIIluiiLaLUICIr
its lower cost. Recent research
,, ---- -- ^
i on foliage plants has shown that fertilizers conts
Although no problem was found when 100% urea or ammonium nitrogen sources and
ns of the two were tested on selected foliage, tests on all genera have yet to be
therefore a small amount of nitrate nitrogen (10-15%) is still recommended for
n flowering crops the use of 25-50% nitrate nitrogen is advised.
Relative levels of nitrogen, phosphorous and potassium in a fertilizer analysis are referred
to as the N-P20O-K20 ratio. Research on plants maintained indoors for extended periods show
that plants grow equally well with 1-1-1 ratio fertilizers such as 14-14-14 and 20-20-20 or 3-1-2
ratio fertilizers like 9-3-6 and 18-6-12. The use of 3-1-2 ratio fertilizers is recommended
because of the cheaper cost per unit of nitrogen and also because the lower total medium soluble
salts levels generated improves a plants' ability to adjust to interior environments.
When preparing fertilizer solutions, remember that liquid fertilizer formulations
containing more than 9 grams/gallon nitrogen may burn foliage. When it is not possible to rinse
off irrigation water containing high concentrations of nitrogen splashed on leaves, consider
dividing the fertilizer application rate in half and making two applications instead of one.
Example: (rates taken from Table 3) 14.2 grams 20-20-20/14 inch pot/4 months can be adjusted
to 7.1 grams 20-20-20/14 inch pot/2 months.
All microelements necessary for foliage plant growth are usually added to most
commercially prepared growing mixes during production. When creating a medium,
microelements must be added and should be thoroughly incorporated. Micromax (Grace Sierra
Co., Milpitas, CA 95035) and Perk (Estech General Chemical Corp., Chicago, IL ) are just two
examples of microelement sources available. Both gave excellent results in experimental plots
when added at the rate of 1 to 1-1/2 lbs/yd3. If micronutrients have not been mixed into the
potting medium, they may be added separately or incorporated into the fertilizer program, either
as a periodic treatment or along with every fertilizer application.
Incorporation of superphosphate into potting media for foliage plants was once a common
practice but is no longer recommended because superphosphate contains 1 to 2% fluoride, a
contaminant which has been shown to cause serious phytotoxicity on the following genera;
Calarhea, Chlorophyrum, Cordyline, Dracaena, Maranta, and Yucca. Research on foliage plants
has shown that incorporation of superphosphate is unnecessary for the production and
maintenance of good quality foliage when other sources of phosphorus are used.
1. Braswell, J.H., T.M. Blessington, and J.A. Price. 1982 Influence of cultural practices
on postharvest interior performance of two species of schefflera. HortScience 17(3):345-
2. Collins, P.C. and T.M. Blessington. 1985. Keeping quality of Ficus benjamin as
affected by production light levels and post production light quality and level.
3. Conover, C.A. and R.T. Poole. 1980. Interior quality of Dracaena angustifolia Roxb.
'Honoriae' as influenced by light and fertilizer during production. HortScience 15(1):24-
4. Conover, C.A. and R.T. Poole. 1981. Incremental growth of two foliage plants
maintained under artificial light levels for one year. Foliage Digest 4(7):5-7.
5. Conover, C.A. and R.T. Poole. 1981. Influence of light and fertilizer level and
fertilizer sources on foliage plants maintained under interior environments for one year.
J. Amer. Soc. Hort. Sci. 106(5):517-574.
6. Conover, C.A., R.T. Poole and T.A. Nell. 1982. Influence of intensity and duration
of cool white fluorescent lighting and fertilizer on growth and quality of foliage plants.
J. Amer. Hort. Sci. 107(5):817-822.
7. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for
production of acclimatized potted foliage plants. University of Florida, IFAS, Central
Florida Research and Education Center Apopka, CFREC-A ;Research Report RH-90-1.
8. Dunn, S. 1975. Lighting for plant growth or maintenance. Florist's Review
9. Henley, R.W. 1989. Selected foliage plants grown for retail markets. Foliage News
14(8): 8pp. University of Florida, Florida Cooperative Extension Service.
10. Henley, R.W. 1989. Major foliage plants utilized by the interior landscape industry.
Foliage News 14(9): 8pp. University of Florida, Florida Cooperative Extension
11. Marchant, Brent. 1982. Basic lighting techniques for interior landscapes. Amer.
12. Turner, Melanie A., David L. Morgan and David Wm. Reed. 1987. The effect of light
quality and fertility on long term maintenance of selected foliage plants. J. Environ.
13. Weiler, T.C., G.M. Pierceall and J.A. Watson. 1982. Light requirements of interior
plants. American Nurseryman. 156(11):39-42.
foliage plants indoors.
s at Varvine Lisht
IV lllghtIneny 75-150 150-225 225
I Name Light Intensity 75-150 150-225 225-500
ma (culuvars) /3 i 2
fa heterophylla 150 1 1
ufCU IC U LL VWU L.J T J
i (species & 150
iorea elegans 75 1 2 2
I < < 1 a
m variegatum 150
achia (species 150
a deremensis 75
a fragrans 150
-i, 1* -
2 z 2
L 2 2
i I 2
150 I 1 2 2
-I ien I 1 I I
elix (cultivars) 150
1 1 1 2
rsrerana 13u i 2 2
(species & 150 1 2 2
ie Light Intensity 75-150 150-:
-_1 _^ 1,r/\4I4
- I -- I
.25 225-500 5
I _ I __ I
vcandens 75 1 1 2 2
a sinica 225
pvnripC ki 17
1 2 2 3
1 2 2 3
oricola 150 1 1 2
1 j 231
ft/yr. Categones are denied as I = 2g, 2 = 4 g, 3 = 6 g, and 4 = g.
A vnva v rf IA-IAA nlA^Ar1. _.1- ~_ r-i."r- 3--- --l A- . I.. __-t_- .c __ f
in vanuus Sicu pots Ior speclnc crops.
Sr gramsb 14-14-14/pot/4 month:
0.8 1.9 3.3 5.2 7.5 10.2
1.2 2.8 4.9 7.8 11.2 15.3
1.6 3.7 6.6 10.4 14.9 20.3
are defined as 1 = 2 g, 2 = 4 g, 3 = 6 g and 4 = 8 g N/ft/yr.
ion 14-14-14 equals approximately 5 grams.