Effects of Medium Temperature and
Magnesium Application Rate on
Growth of Philodendron scandens oxycardium

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University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC - Apopka Research Report, RH-91-18

R.T. Poole*

Magnesium, one of the macro elements utilized by plants during photosynthesis, is most frequently supplied by incorporation of dolomite or magnesium sulfate into potting mixtures during the manufacturing process. Philodendron scandens oxycardium (Heart-leaf philodendron) sometimes develops magnesium deficiency symptoms, also called bronzing disease, during production. Plant growth slows and stems are unusually thin with short internodes. The leaves of affected plants are smaller than normal, with yellowish green markings appearing on older leaves first, in the inverted "v" shape which are typical magnesium deficiency symptoms for many foliage plants. These symptoms seem to appear more frequently in the winter months when medium temperatures are lower. As medium temperature affects the plant's ability to extract essential nutrients, most foliage plants grow best when medium temperatures are between 70 and 80°F. The following research was conducted to examine the effects of medium temperature and magnesium application rate on growth of heart-leaf philodendron plants and growth of cuttings harvested from treated plants.

Materials and Methods

Experiment 1, a 3 x 4 factorial experiment with 8 replications, was initiated on 22 February 1991 when heart-leaf philodendron plugs obtained from a local grower were transplanted into 6 inch plastic pots containing Florida sedge peat amended with 3.5 lbs/yd³ CaNO₃. Maximum medium temperature was maintained at 60, 65, 70 and 75°F by placing pots in forced-air chambers specially designed for that purpose. These forced-air chambers were located in a greenhouse where minimum air temperature was 60°F and maximum light intensity at bench level was 1500 ft-c. The test plants were watered as needed, 2 to 3 times per week. 19-6-12 Osmocote (Grace-Sierra Co., Milpitas, CA 95035), a 3 month release rate fertilizer, was surface applied to pots on 25 February 1991. A medium drench of 5 g Mg(SO₄) per liter of water was applied to pots at rates of 0, 100 or 200 ml/pot in order to obtain the Mg(SO₄) application rates tested, 0, 0.5 and 1.0 g/6 inch pot.

Initial and final average vine length (cm) for the four largest vines per plant were recorded on 22 February and 23 May, respectively. Electrical conductivity (µmhos/cm) and pH of the leachate from pots containing heart-leaf philodendron were determined initially and at 6 week intervals until 25 May.

On 23 May, cuttings were obtained from the heart-leaf philodendron stock plants grown in this test. Cuttings were propagated, 5 per 5 inch container, in Vergro Container Mix A (Verlite Co., Tampa, FL 33680). Cuttings were placed under intermittent mist, on a propagation bench, in a greenhouse where air temperatures ranged from 60 to 90°F and maximum light intensity was 2200 ft-c. On 15 July, cuttings were moved to a bench in a greenhouse where temperatures ranged from 60 to 90°F and maximum light intensity was 3000 ft-c. Fertilizer was surface applied to medium on 16 July, when each pot received 2.5 g/5 inch pot 19-6-12 Osmocote. Total vine length (cm) and number of nodes per plant were determined on 17 September 1991, the day the experiment was terminated.

Results and Discussion

Vine length of stock plants was significantly affected by medium temperature, with length increasing as medium temperature increased (Table 1). The magnesium application rates tested did not affect plant growth. Plants subjected to the highest medium temperature tested, 75°F, produced longer vines regardless of magnesium rates. All plants were watered with central Florida ground water containing approximately 15 ppm Mg. Theoretically, these Mg levels could have been enough to prevent magnesium deficiency symptoms from developing on the plants which did not receive Mg(SO₄).

The electrical conductivity of leachate from the medium generally tended to decrease as medium temperatures rose and increase as magnesium application rates increased (Table 2). The pH (not shown) of media from all treatments was about 4.4 at the start of research, but had increased to around 5.4 by the time the experiment was terminated on 25 May 1991.

Growth of cuttings was not affected by medium temperature or magnesium levels stock plants received. Total vine length averaged 204 cm and number of nodes averaged 43 on the four longest vines of cuttings grown from plants receiving the 3 magnesium levels and 4 medium temperatures.

A 15°F rise in minimum medium temperature, from 60 to 75°F significantly increased growth of heart-leaf philodendron vines, demonstrating bottom heating systems' ability to shorten production time for heart-leaf philodendron crops during the winter months in Florida.

*Professor of Plant Physiology, Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, Fl 32703-8504.

Additional Reading

1. 1. Conover, C.A., L.S. Osborne and A.R. Chase. 1984. Heart-leaf Philodendron. Nurseryman's Digest 18(5):91-94.

   2. Conover, C.A. and R.T. Poole. 1974. Influence of shade and fertilizer source and level on growth, quality and foliar content of Philodendron oxycardium Schott. J. Amer. Soc. Hort. Sci. 99(2):150-152.

   3. Conover, C.A. and R.T. Poole. 1981. Guide for fertilizing tropical foliage plant crops. Univ. of Fla., IFAS, CFREC-Apopka Res. Rpt. RH-81-1.

   4. Conover, C.A. and R.T. Poole. 1987. Growth of Dieffenbachia maculata 'Perfection' as affected by air and soil temperatures and fertilization. HortScience 22(5):893-895.

   5. Dicky, R.D. and J.N. Joiner. 1966. Identifying elemental deficiencies in foliage plants. Fla. Foliage Grower 3(5): 1-2.

   6. Ingram, D.L., C. Ramcharan and T.A. Nell. 1986. Response of container-grown banana, ixora, citrus and dracaena to elevated root temperatures. HortScience 21(2):254-255.

   7. Joiner, J.N., C.A. Conover and R.T. Poole. 1981. Nutrition and fertilization. p.229-268. In: J.N. Joiner (ed.). Foliage Plant Production. Prentice-Hall, Englewood Cliffs, NJ.

   8. Koller, D.C., L.K. Hiller and R.W. Van Denburgh. 1980. A forced-air system for controlling soil temperatures in plastic pots. HortScience 152):189-190.

   9. Poole, R.T. and C.A. Conover. 1976. Chemical composition of good quality tropical foliage plants. Proc. Fla, State Hort. Soc. 89:307-308.

1. Table 1. Average length of four longest Philodendron scandens oxycardium vines from plants receiving Mg(S0₄) applied at rates of 0, 0.05 and 1.0 g/6" pot and soil temperatures of 60, 65 70 and 75°F, grown from 22 February until 23 May 1991.

1. ^Zns, **; Results nonsignificant significant at P = 0.01, respectively.

1. Table 2. Electrical conductivity (µmhos/cm) of medium leachate from 6" pots containing Philodendron scandens oxycardium treated with 0, 0.5 and 1.0 g/ pot Mg(SO₄) and soil temperatures of 60, 65, 70 and 75°F, grown from 22 February until 23 May 1991.

1. Zns, *, **; Results nonsignificant, significant at P = 0.5 and 0.01, respectively.