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used only to trace the historic work of
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Copyright 2005, Board of Trustees, University
of Florida

I6 3&3 1 2/7

Heat Stress of Foliage Plants Central Science
Library
R. T. Poole and C. A. Cdnover
University of Florida, IFAS, OCT 1.4 1987
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Repor RHyI9Ssity of FIoI ,i

The deleterious effect of high temperatures on plants has eeFsTrg-
known, but only recently has there been concern regarding the economics of
reducing high temperatures. Many commercial foliage plant growers utilize
some method of cooling production areas during summer to maintain optimum
growth and quality of foliage plants. Some growers try to maintain
maximums as low as 80F while others set thermostats as high as 95F.

Earlier research has shown that some foliage plants grow
satisfactorily at high air temperatures (100-110F) while others grow best
at cooler temperatures (90F) (Foliage Digest V(1):9-10 and Foliage Digest
VIII(4):8).

As a part of other research, a 3 x 4 experiment was initiated in the
spring of 1986 to test various levels of fertilizer; the recommended rate
(Foliage Digest VII(8):1-6), 2 times the recommended rate and 3 times the
recommended rate and maximum air temperatures of 90, 95, 100 and 105*F on
growth of foliage plants not previously tested under high temperatures.

Test plants included Aeschynanthus pulcher (Lipstick Plant), Calathea
'Argentea' (Silver Portrait Calathea), Codiaeum variegatum (Croton
'Petra'), Epipremnum aureum (Pothos), Maranta leuconeura (Green Maranta),
Peperomia obtusifolia (Green Peperomia) and Philodendron scandens
oxycardium (Heart-leaf Philodendron). Fertilizer was supplied as 19-6-12
Osmocote. Plants were potted in 6 inch azalea pots containing Vergro
container mix and placed in sections of a greenhouse where temperature
maximums were controlled by a fan and pad cooling system. Philodendron and
Peperomia were potted March 13, 1986, Maranta and Pothos, May 5, and
Lipstick Plant, Croton and Silver Portrait Calathea June 16. The
greenhouse located at CFREC-Apopka allowed about 1500 ft-c maximum to reach
the plants. Plants were watered sufficiently so that water stress was not
a factor.

Plant grade and growth measurements of all plants decreased as maximum
temperatures increased (Table 1). Grades for Calathea and Pothos were
least affected. Grades for Philodendron and Maranta were about the same
for maximum temperatures of 90-1000F, but there was considerable difference
between grades of Maranta and Philodendron grown under 100 or 105F
maximum. Grades of Croton and Peperomia grown at 100 or 105F maximum were
considerably less than plants grown at 90 or 95F maximum. Lipstick plants
grown at 95F maximum or above had a poor grade compared to 90F maximum.
Fresh weight or height was highest for all plants grown at 90*F except for
Calathea and Maranta where maximum growth was observed at 95F.

Professor of Physiology and Professor and Center Director, respectively,
Central Florida Research and Education Center, 2807 Binion Road, Apopka,
FL 32703.

Plant grade of most plants was not affected by variations in
fertilizer level. Lipstick plants showed a slight decrease in grade, while
Calathea, Pothos and Peperomia a slight increase as fertilizer level
increased. Fresh weight of Lipstick Plant and Philodendron decreased as
fertilizer levels increased, but fresh weight of Pothos and Peperomia
increased.

The pH and soluble salts of the Peperomia mix as determined by the
pour-through method (Foliage Digest IX(12):6) did not change with changes
in maximum temperature. As fertilizer level increased, pH decreased and
soluble salts increased. If pH and soluble salts of the mixes containing
the other plants were similar to Peperomia, a comparison of Tables 1 & 2
indicates that Calathea, Croton, Pothos, Maranta and Peperomia will grow
satisfactorily over a wide range of soluble salts and pH.

Suggested maximum temperature of some foliage plants is found in Table
3. Optimum and economical maximum temperatures will vary with duration of
high temperatures, cost of electricity and profitability of plants
produced. This research should aid producers in selecting upper limits for
fan and pad cooling systems. This research as well as previous data we
have collected indicates that cooling below 95F is not beneficial for most
foliage crops. However, cooling to 90F or below may be beneficial in
increasing labor productivity.

-2-

Table 1. Harvest dates of summer grown foliage plants with greenhouses cooled at various maximum temperatures 1986.

Green
Maranta
Plant Fresh
grade wt (g)
4.4 101

4.6 124

4.2 102

3.6 73

July 16
Green
Peperomia
Plant Fresh
grade wt (g)
4.8 371

4.5 346

3.8 314

3.5 291

Heart-leaf
Philodendron
Plant Fresh
grade wt (g)
4.4 157

4.4 148

4.3 140

3.2 92

Lipstick
Plant
Plant Fresh
grade wt (g)
3.5 144

2.2 77

2.4 41

2.2 34

September 12
Silver
Portrait Calathea
Plant Plant Pl
grade ht (cm) g9
4.0 58 4.

3.8 61 4,

3.8 53 3

3.7 51 3,

Croton
'Petra'
plant Plant
trade ht (cm)
.2 43

.5 41

.5 32

.3 31

Pothos
Plant Fresh
grade wt (g)
4.7 308

4.6 253

4.8 264

4.5 242

Fertilizer
level

x

2x

3x

al = Poor, unsalable, 5 = excellent quality.
x = 3.3 g 19-6-12 Osmocote 6" pot every 3 months
and Lipstick Plant and 5.9 g for Croton.

for Maranta, 1.7 g for Peperomia, 4.2 g for Philodendron, Pothos, Calathea

Maximum
temp ("F)
90

95

100

105

4.0

4.3

4.6

278

352

361

4.1

4.1

4.1

148

128

127

2.9

2.5

2.4

3.6

3.9

4.0

229

283

287

Table 2. Micromhos/cm and pH of Peperomia
pour-through method.

container mix 1986, using the

Plants fertilized March 13 and June 13, 1986
Maximum pH Micromhos/cm
temp (F) 14 May 12 June 9 July 14 May 12 June 9 July

90 4.2 3.9 3.8 2033 1328 1405
95 4.2 4.2 4.0 2136 1490 1514
100 4.4 4.5 4.0 2145 1655 1460
105 4.5 4.4 4.0 1878 1252 1521

Fertilizer
levels

xa 6.0 5.8 6.0 520 273 252
2x 5.2 5.2 5.0 1762 1191 1206
3x 3.9 3.8 3.5 3862 2830 2967

x = recommended rate (Foliage Digest VII(8):1-6).

-4-

Table 3. Suggested maximum temperature
foliage plants.

Plant name
Aeschynanthus pulcher
(Lipstick Plant)

Aglaonema commutatum 'Silver Queen'

Calathea 'Argentea'
(Silver Portrait Calathea)

Calathea makoyana
(Peacock Plant)

Chamaedorea elegans
(Neathe Bella Palm)

Codiaeum variegatum
(Croton 'Petra')

Dieffenbachia maculata 'Perfection'

Dracaena marginata

Epipremnum aureum
(Pothos)

Ficus benjamin
Weeping Fig)

Maranta leuconeura
'(Green Maranta)

Nephrolepis exaltata
(Boston Fern)

Peperomia obtusifolia
(Green Peperomia)

Philodendron scandens oxycardium
(Heart-leaf Philodendron)

for growth of some

-5-

Temperature F
90

100

95

95

95

95

90

95

90

100

95

90

95

95