Effects of Production Light Intensity, Fertilizer Treatment and Interior Light Intensity on Ctenanthe 'Loursii'
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C.A. Conover, Ph.D.*
University of Florida/IFAS
Central Florida Research and Education Center
CFREC-Apopka Research Report RH-95-6
Ctenanthe 'Loursii' is a tropical foliage plant from the Marantaceae family. Foliage is variegated cream, light green and medium green. Plants grown in large containers can reach a maximum height of about 4 feet. South Florida nurseries grow Ctenanthe 'Loursii' in 8-inch or larger containers, as well as in smaller pots, for use as specimen plants in tropical and protected sub-tropical outdoor landscapes (climate zones 10B to 11).
Plants are also starting to be utilized in interior installations. However, the tendency to develop necrotic spots in the cream colored areas of leaves is a problem for interiorscapers. Since growing regimes producing plants acclimatized to indoor conditions have been developed for other members of the Marantaceae family closely related to Ctenanthe 'Loursii', (maranta and stromanthe) we decided to determine the potential of this plant for interiorscape use.
Experiment 1 was initiated January 14, 1992, when large Ctenanthe 'Loursii' specimen plants, growing in 10-inch (25-cm) containers, were obtained from a south Florida nursery. Plants were immediately placed in simulated interiorscape environments where temperatures ranged from 70 to 80°F (21.1 to 26.7°C) under light intensities of 50, 100 or 150 ft-c (8, 16 or 24 µmol-2•s-l). Leaves with brown necrotic spots mostly in the cream colored areas of the leaf were removed.
On May 14, 1992, after 120 days in simulated interiorscape conditions, plants were rated using a quality scale of 1 = dead, 2 = unattractive, 3 = some loss of original quality but still attractive, 4 = very attractive, losing quality slowly and 5 = comparable to or better than original quality. Number of leaves per plant with brown necrotic spots in cream colored areas of the leaf was determined May 20, 1992, and experiment 1 was terminated.
Experiment 2 was initiated June 12, 1993, using small Ctenanthe 'Loursii' plants grown from tissue culture and rooted in 4-inch (10-cm) pots. Plants were transplanted into 6-inch (15cm) plastic tub pots using Fafard #4 growing medium (Fafard of Florida, Inc., 3723 Hogshead Rd, Apopka, FL 32703) amended with 1 lb/yd3 (0.59 kg/m3) Micromax (The Scotts Company, 6656 Grantway, Allentown PA 18106). Plants were placed in a glass greenhouse where air temperatures were maintained between 65 and 90°F (18.3 and 32.2°C) and maximum light intensity was 1500 to 2000 ft-c (266 to 355 µmol-2•s-1).
Nitrogen, potassium and phosphorous used in fertilization were obtained from stock solutions. Ctenanthe were fertilized one time per week, with 60 ml (2 oz) of liquid fertilizer solution applied to each container. Nine fertilizer treatments were tested, with five replications per treatment. Each treatment provided 3.14 g N/6-inch pot/yr (1.1 oz N/15-cm pot/yr). The liquid feed contained NH4, NO3, urea, or various combinations of NO3 with the other two sources (see Table 2).
Plant height was measured initially July 2, 1993. Final plant height and width were measured October 8, 1993. Plants were graded October 26, 1993, based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality, and 5 = excellent quality.
Experiment 3, initiated January 3, 1994, was a 4 nitrogen rate x 4 potassium rate factorial test, with 5 replications per treatment to determine the influence of N and K ratios on Ctenanthe 'Loursii'. Small starter plants were obtained by dividing the plants grown from tissue cultured liners used in experiment 2. Rooted Ctenanthe 'Loursii' were transplanted into 6-inch (15-cm) plastic tub pots December 8, 1993, using Fafard #4 growing medium amended with 1 lb/yd3 (0.59 kg/m3) Micromax. Plants were placed in a glass greenhouse, where maximum light intensity was 1000 ft-c (178 µmol m-2•s-1) and air temperatures were maintained between 65 and 90°F (18 and 32°C). Plants were watered using overhead irrigation when needed.
Ctenanthe 'Loursii' were fertilized once a week with 100 ml/6-inch pot (3.4 oz/15-cm pot) liquid feed made from stock solutions. Plants were fertilized so that each received 0.82 g P, 1.85, 3.07, 4.30 or 5.52 g N and 1.85, 3.07, 4.30 or 5.52 g K/6-inch pot/yr (0.29 oz P, 0.65, 1.10, 1.52 or 1.94 oz N and 0.65, 1.10, 1.52 or 1.94 oz K/15-cm pot/yr).
Number of Ctenanthe 'Loursii' leaves with necrotic spots in the cream colored areas of leaves was determined March 23, 1994. Final pH and electrical conductivity of the leachate collected from the growing medium was recorded. Seventy-nine days after fertilizer treatments were initiated, March 23, 1994, plants were graded using the same scale used in experiment 2, and experiment 3 was terminated.
Experiment 4 was a 4 shade level x 4 fertilizer rate test. The experiment was initiated March 31, 1994, when Ctenanthe 'Loursii' grown in experiment 3 were transplanted into standard 3-gal (11.4 L) nursery containers using a growing medium composed of Florida peat:pine bark:builder's sand (6:3:1 by volume). Growing medium was amended with 7 lb/yd3(4.2 kg/m3) dolomite and 1.5 lb/yd3 (0.89 kg/m3) Micromax.
Plants were grown to large specimen size in a shadehouse under 50, 60, 70 or 80% shade provided by black shadecloth. Air temperature ranged from 45 to 95°F (7 to 35°C). Light levels, measured April 18, 1994, and again August 1, 1994, ranged from 4000 to 5800 ft-c (711 to 1031 µmol -2• s-1) under 50% shade, from 3000 to 4600 (533 to 817 µmol-2• s-1) under 60% shade, from 2200 to 3800 ft-c (391 to 675 µmol-2• s-1) under 70% shade and from 1800 to 2400 (320 to 426 µmol-2• s-1) under 80% shade. Containers were top-dressed April 1, 1994, with 19-6-12 Osmocote (The Scotts Company, 6656 Grantway, Allentown, PA 18106). Fertilizer rates tested were equivalent to 1500, 2100, 2700 or 3300 lb N/A/yr (8.5, 11.9, 15.4 or 18.7 g N/3-gal pot/yr). Plants were watered overhead manually as needed to maintain healthy growth.
Plant height and width were measured July 7, 1994. For quantitative purposes, plant size was defined using the formula: (height + width) / 2 = plant size. Plant grades were determined when the production phase of this experiment was completed, using the same scale as in experiments 2 and 3. Electrical conductivity (µmhos/cm) and pH of leachate collected from the growing medium of Ctenanthe 'Loursii' were determined July 22, 1994.
Plants were moved to interior environment rooms July 26, 1994, where typical interior conditions were simulated. Cool white fluorescent lighting provided a light intensity of 150 ft-c (24 µmol-2• s-1) and air temperatures ranged from 70 to 80°F (21 to 27°C). While in rooms, plants were watered as needed to maintain the proper medium moisture level.
The number of leaves with necrotic spots in the cream colored areas of the leaf was determined on August 16, August 29 and September 28, 1994, and spotted leaves were removed from plants each time a count was taken. Plants were graded September 28, 1994, using the same grading scale used after shadehouse production. Plant grade change during simulated interiorscape use was determined by subtracting the interior plant grade from the production plant grade.
Plant size after interiorscape use, determined when research was terminated September 29, 1994, was defined by the formula: (height + width) / 2 = plant size. Size change during simulated interior use was defined as plant size after interiorscape use - plant size after shadehouse production phase.
Results
Experiment 1. Although quality loss was observed for all plants tested, plant grade decreased as indoor light intensity increased, so that only plants under 150 ft-c were still considered very attractive after 120 days indoors (Table 1). Ctenanthe maintained in 100 ft-c rooms for 120 days were rated attractive and those in low light rooms (50 ft-c) were considered to be unattractive. Number of leaves with necrotic spots increased as interior light intensity decreased (Table 1).
Experiment 2. Examination of final height, number of leaves, tipburn damage and plant grade data proved inconclusive. However, plants fertilized with 100% nitrate, 50% nitrate: 50% urea or 75% nitrate: 25% urea received somewhat lower plant grades but had less tipburn than plants fertilized with other treatments. The same trend (foliage tipburn caused by ammonical fertilizer) has been observed with other genera in the Marantaceae. Generally, the overall quality as reflected in plant grades was poorer for plants getting 50% or more N from NO3 and no NH4 when compared to quality of 'Loursii' getting other fertilizer treatments (Table 2).
Experiment 3. Fertilizer treatments did not affect number of leaves with necrotic spots after 79 days of treatment (data not shown). Average number of leaves with necrotic areas was 2.8 per plant.
Plant grade was good when plants received 3.07 g N/6-inch pot or more, but plants getting the low N rate (1.85 g), were in unsalable condition when the experiment was terminated (Table 3). Potassium rate did not significantly influence plant grade. Electrical conductivity of growing medium leachate was overall on the low side but did increase as total fertilizer rate increased, due to increased fertilizer salts in growing medium.
Experiment 4. Production plant grades showed quality of plants grown under 60 or 70 % shade, was higher than quality of plants grown under 50% or 80% shade (Table 4). Plants grown under 60 or 70% shade also deteriorated less rapidly during simulated interior use compared to plants grown under 80% shade. Even though change in grade of Ctenanthe 'Loursii' produced with 50% shade showed a slight increase after simulated interior use compared to the decrease in plant grades observed for plants grown in higher shade, plant quality was still lower compared to quality of plants produced in 60 or 70% shade (Table 4). Plant grades recorded after the greenhouse production phase increased as fertilizer rate increased, but those recorded after 'Loursii' was maintained for 64 days in the simulated interiorscape show plants deteriorated more rapidly under interior conditions as production fertilizer rate increased.
Plant size determined after shadehouse production showed size increased as both shade level and fertilizer rate increased (Table 5). Production shade level continued to affect plant size when measured after simulated interior use but fertilizer rate did not.
An interaction of shade level and fertilizer rate affected number of leaves with necrotic areas on August 29, during simulated interiorscape use (Table 6). Data indicate leaf necrosis increases with increasing fertilizer when 'Loursii' are grown under low shade levels, but not when plants are produced under higher shade. This is related to the level of acclimatization to the interior environment being higher for plants grown under 70 or 80% shade. Main effects of shade and fertilizer on necrotic leaves are also shown (Table 7). Leaves of plants grown under 50 or 60% shade have more necrosis than leaves of plants grown under higher shade levels. However, main effects of fertilizer generally follow the trend of more fertilizer equals higher number of necrotic leaves on dates other than shown in the interaction table (Table 6).
Conclusions
Interiorscape companies rely on foliage plants that require a minimum of maintenance to remain in good condition in interior installations. The development of necrotic spots in leaves of Ctenanthe 'Loursii' during production and under interiorscape conditions was observed on the donated fully grown specimen plants we started with in experiment 1 and on plants we grew from tissue culture and cuttings in subsequent tests. Although foliage was not spot free, the condition did improve dramatically when plants were grown under 60 to 70% shade compared to 50% shade. Plants produced in experiment 4 getting the low fertilizer rate, 1500 lb/A/yr, were of good quality and developed less necrosis.
Necrotic spots were also much less of a problem when plants were maintained under the highest interior light level tested, 150 ft-c, which is the minimum level recommended when related foliage plants such as calatheas and stromanthe are maintained in interiorscapes. If production regimes properly acclimatize Ctenanthe 'Loursii' they should make good specimen plants for medium to high light interiorscape sites.
References
- Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. Nursery Digest 24(10):34-36, 58-59.
- Conover, C.A., R.T. Poole and R.W. Henley. 1991. Light and fertilizer recommendations for the interior maintenance of acclimatized foliage plants. Foliage Digest 16(11):1-4.
Table 1. Effects of interior light intensity on Ctenanthe 'Loursii' maintained in a simulated interior environment from January 14 until May 14, 1992. Experiment 1.
Light intensity (ft-c) Plant gradez Necrotic leavesy 50 2.8 11.5 100 3.8 8.0 150 4.1 4.1 Significance linear ** ** zPlants were rated May 14, 1992, using a quality scale of 1 = dead, 2 = unattractive, 3 = some loss of original quality but still attractive, 4 = very attractive, losing quality slowly and 5 = comparable to or better than original quality.
yThe number of leaves with brown necrotic spots was counted May 20, 1992.
xns, **; Nonsignificant or significant at P
Table 2. Effects of nitrogen source on Ctenanthe 'Loursii' grown from June 12 until October 26, 1993. Experiment 2.
N source and % Treatment N&% NH4 N&% NO3 N&% Urea No. leavesz Tip-burny Plant gradex 1 100 0 0 33.4abw 7.2ab 4.7ab 2 75 25 0 33.0ab 6.0abc 5.0a 3 50 50 0 36.2a 6.2abc 4.9a 4 25 75 0 38.0a 7.6a 4.7ab 5 0 100 0 29.0b 4.0bc 4.4bc 6 0 0 100 33.4ab 3.4c 4.9a 7 0 25 75 34.2ab 4.2abc 4.9a 8 0 50 50 32.6ab 3.8bc 4.2c 9 0 75 25 29.6b 3.0c 4.4bc Significance P P P zTotal number of leaves per plant was determined October 8, 1993.
yNumber of leaves with tipburn was determined October 26, 1993.
xPlants were graded October 26, 1992, based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
wMean separation in columns by Duncan's multiple range test, 5% level.
Table 3. Effects of N or K fertilization rate on Ctenanthe 'Loursii' plant grade and pH and electrical conductivity of leachate from container growing medium seventy-nine days after initiation of fertilizer treatments. Experiment 3.
N rate, g/6-inch pot/yr Plant gradez pHy EC (µmhos/cm) 1.85 2.9 6.0 478 3.07 4.0 6.2 714 4.30 4.1 6.2 982 5.52 4.4 5.9 2229 Significancex linear ** ** ** quadratic ** ** ** K rate, g/6-inch pot/yr 1.85 3.8 6.2 648 3.07 3.9 6.0 960 4.30 3.9 6.1 1336 5 52 3.8 6.1 1460 Significancex linear ns ns ** zPlants were graded March 23, 1994, using a scale of 1 = dead, 2 - poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
yFinal pH and electrical conductivity of leachate collected from the growing medium were determined on March 23, 1994.
xns, **; Nonsignificant and significant at P < 0.01, respectively.
Table 4. Effects of production shade or fertilizer levels on production plant grade, interior plant grade and plant grade change after simulated interior use. Experiment 4.
Shade level (%) Production plant gradez Interior plant gradey Plant grade changex 50 3.8 3.9 + 0.1 60 4.5 4.2 -0.3 70 4.5 4.3 -0.2 80 4.0 3.6 -0.4 Significancew linear ns ns ** quadratic ** ** ns Fertilizer rate, lb N/A/yr 1500 3.7 3.8 + 0.1 2100 4.1 4.1 0.0 2700 4.4 4.1 -0.3 3300 4.5 4.0 -0.5 Significancew linear ** ns ** zPlants were graded July 22, 1994, after greenhouse production, using a scale of 1 = dead, 2= poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
yPlants were graded September 28, 1994, after simulated interior use, using the scale described above.
xPlant grade change was determined using the formula: production plant grade - interior plant grade = plant grade change.
wns, **; Nonsignificant or significant at P < 0.01, respectively.
Table 5. Effects of production shade or fertilizer levels on plant size after greenhouse production, plant size and change in plant size after simulated interior use. Experiment 4.
Shade level (%) Production plant sizez(cm) Interior plant sizey Plant size changex 50 79 83 4 60 80 85 4 70 93 102 9 80 101 114 12 Significancew linear ** ** ** quadratic * * ns Fertilizer rate, lb N/A/yr 1500 84 93 8 2100 87 95 7 2700 90 96 7 3300 92 100 7 Significancew linear * ns ns zproduction height and production width were measured July 7, 1994, after greenhouse production. Production plant size was defined using the formula: (height + width) / 2 = production plant size.
yInterior height and interior width were measured when research was terminated September 29, 1994. Plant size after simulated interior use was determined using the formula: (interior height + interior width) / 2 = interior plant size.
xSize change after simulated interiorscape use was defined as plant size after interiorscape use plant size after shadehouse production.
wns, *, **; Nonsignificant, significant at P
Table 6. Effects of interaction of shade and fertilizer levels on number of necrotic leavesz on Ctenanthe 'Loursii' determined on August 29, 1994. Experiment 4.
Fertilizer rate, lb N/A/yr Shade level (%) 1500 2100 2700 3300 50 7.2 7.5 9.0 14.8 60 5.2 10.0 17.5 14.0 70 4.5 7.5 4.2 4.8 80 1.5 0.5 1.8 2.7 Interaction significant at P
zCtenanthe 'Loursii' leaves with necrotic spots in the cream colored areas of the leaf were removed and counted three times while plants were in interior environment rooms. The damaged leaves were removed on August 16, August 29 and September 28, 1994.
Table 7. Effects of production shade or fertilizer levels on number of Ctenanthe 'Loursii' leaves with necrotic areas. Experiment 4.
Shade level (%) Necrotic leavesz Jul 7 Necrotic leavesy Aug 16 Necrotic leavesx Sep 28 50 1.9 32.9 19.4 60 2.0 33.9 23.3 70 0.4 17.8 13.5 80 0.1 12.8 7.1 Significancew linear ** ** ** quadratic ns ns * Fertilizer rate, lb N/A/yr 1500 1.8 22.1 12.4 2100 0.8 23.8 12.1 2700 0.8 26.2 17.2 3300 0.9 25.3 21.6 Significancew linear * ns ** zNumber of leaves per plant with necrotic spots in the cream colored areas of leaves was determined July 7, 1994, after greenhouse production. Leaves were not cut off plants at this time but necrotic areas were marked with a waterproof marking pen.
yleaves with necrotic spots in the cream colored areas of the leaf were counted and then removed August 16, 1994.
xLeaves with necrotic spots in the cream colored areas of the leaf were counted and then removed September 28, 1994.
w ns, *, **; Nonsignificant, significant at P
* Professor of Environmental Horticulture and Center Director, (retired 7/96) Central Florida Research and Education Center, 2807 Binion Road, Apopka, FL 32703-8504.