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Morphological responses of bedding plants to three greenhouse temperature regimes
SCIENTIA HORTICULTUM Scientia Horticulturae 60 ( 1995 ) 3 13-324
Morphological responses of bedding plants to three greenhouse temperature regimes Richard H. Merritt”,*, KC. Tingb =Departmentof Plant Science, New Jersey Agricultural Experiment Station, Rutgers University,New Brunswick, NJ 08903, USA bDepartment of Bioresource Engineering, New Jersey Agricultural Experiment Station, Rutgers University,New Brunswick, NJ 08903, USA
Accepted 2 August 1994
Abstract Seedling crops of gazania, geranium, marigold, mimulus, pansy, verbena and vinca were grown to 60% anthesis in three greenhouse temperature regimes: (a) 26°C day/6 k 3°C night (LT),witha 16.5”Cmeandailytemperature (MDT), (b) 26”Cday/l7+4”Cnight,
with a 2 1“C MDT, and (c) variable day/night temperatures in response to heating and cooling by a phase change material energy storage module (PCM) with an 8 If:2’ C night and a 16oC MDT. Crops bloomed from 2 to 17 days earlier in the 26”C/ 17 ” C greenhouse. The morphological characteristics of all cultivars of gazania, mimulus, pansy and verbena, geranium and vinca were similar regardless of greenhouse temperature regime. Marigold diploid and triploid cultivars and mimulus were morphologically more variable than the other bedding plant species. Crops grown in the PCM and LT greenhouses had virtually identical morphological characteristics and bloomed in about the same number of days. Plant height was not affected by DIF environments in the greenhouses. The PCM and LT greenhouses had a similar MDT, but the distribution of numbers of hours of mean daily temperatures was different. Keywords: Energy conservation; Flowering; Gazania (Gazania splendens); Geranium (Pelarganium x hortorum); Height; Low night temperatures; Marigold (Tagetes patula and Tagetes erectaxpatula); Mimulus (Mimulusx hydrides); Pansy ( Violax Wittrockiana);Phase change material energy storage unit; Verbena ( Verbenax hybrida); Vinca (Catharanthus roseus)
* Corresponding author. 03044238/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
SSDIO304-4238(94)00714-4
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1. Introduction Research studies have evaluated energy conservation approaches and their effect on growth and development of several bedding plant crops (Merritt and Kohl, 199 1; Lieth et al., 199 1). The goals of this research were ( 1) to identify bedding plants that will grow to be compact, well branched and to have large numbers of flowers when grown at low ambient temperatures normally associated with spring bedding plant production in New Jersey, (2) to identify plant germplasm that will have minimal or no delay in blooming when grown at low temperatures and (3 ) to minimize heat energy costs. Morphological characteristics of bedding plants when the crop was at 60% anthesis were evaluated in response to three greenhouse temperature regimes, two of which focused on minimizing fossil fuel use either by low night temperature or by substituting a phase change material energy storage module (PCM) designed to collect and store solar energy during the day and to release heat energy at night (Giacomelli et al., 1990; Ting et al., 1990; Wu, 199 1). Another objective was to evaluate crop growth and development responses to greenhouse temperatures which could vary greatly due to the PCM operation. Studies with marigold, pansy, petunia and verbena have shown that they can be grown with desirable morphological characteristics at low night temperatures with reduced heat energy costs and with minimal delay in blooming (Merritt and Kohl, 1989, 199 1). Temperature and light may also affect growth and flowering of baby’s breath. Night temperatures below 8 “C and a low photosynthetic photo flux affected anthesis of one cultivar but not another, indicating cultivar variation in response to temperature (Hicklenton et al., 1993a,b).
2. Materials and methods Visually matched crops of gazania (Gazania splendens, cultivars ‘Ministar White’, ‘Daybreak Garden Sun’, ‘Talent Yellow’, ‘Talent’ mix), geranium (Pelarganiumx hurtorumcultivar ‘Red Elite’), marigold ( Tagetespatula,cultivars ‘Early Queen Sophia’, ‘Aurora Yellow’), (Tagetes erectaxpatula, cultivars ‘Spinner’, ‘Zenith Yellow Crested’, ‘Mighty Marietta Orange’, ‘Yellow Nugget Supreme’), mimulus (Mimulusx hydridus, cultivars ‘Royal Velvet’, ‘Yellow Velvet’, ‘Calypso’ Mix, ‘Mystic’ Mix), pansy ( Viulax Wittrockianacultivars ‘Accord Yellow Blotch’, ‘Accord Blue Blotch’, ‘Ultima Pink’, ‘Ultima Beacon Bicolor’, ‘Maxim Yellow’, ‘Fama See Me’, ‘Fama Red’), verbena ( Verbenax hybrida cultivars ‘Imagination’, ‘Rosy Red’), and vinca (Catharanthus ruseus cultivar ‘Little Blanche’) were selected at first true leaf stage and grown until 60% of the crop had reached anthesis. Research was conducted 22 January to 26 May 1993 in three adjacent air-inflated double polyethylene (colorless 6 mil Nutrogro by Visgreen plastic) greenhouses, each 8.5 mx 14.6 m, oriented N-S. The low night temperature greenhouse (LT) had heat added when the air temperature dropped below 26 “C during the daytime hours of 08 : 00- 17 : 00. Exhaust fans were set at
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32 “C. From 17 : 00 to 08 : 00 h no heat was added until the temperature reached 3 “C. The higher night temperature greenhouse (NT) had the same daytime heat and exhaust fan settings as the LT greenhouse. The 17 : 00-08 : 00 heat setting was 18’ C. The phase change module greenhouse (PCM) was not heated during the entire 24 h period unless the temperature went below 3 “C. Exhaust fans were set at 35 “C. The heating and venting temperature targets were usually attained, but on very sunny or cold windy days the heat and ventilation systems often did not provide the heat or cooling necessary to meet the temperature targets. Solar energy collected and stored for later release by the PCM provided most of the heat for the PCM greenhouse. The phase change material was Glauber’s salt (Na,SO,* 1OH20), sodium carbonate decahydrate ( Na2C03* 1OH20), nucleating and stabilizing agents. The mixture had a design phase change temperature of 16‘C to enable the PCM to collect and store solar energy during daytime hours and to release this heat energy to the greenhouse during night-time hours (Merritt and Ting, 1994). Previous studies (Giacomelli et al., 1990; Wu, 199 1) have evaluated plant growth in PCM-heated and -cooled greenhouses. The PCM unit contained 660 kg of phase change material packaged in 44 tube-sheets in a design similar to the unit described in Ting et al. ( 1990). A 250 W fan (Dayton Venture) (0.25 KWH h- ’ ) was installed and operated continuously to provide an airflow of 1.274 m3 s-’ through the unit. The operation of the fan motor increased air temperature in the PCM greenhouse by about 0.2”C. Air served as the energy carrying medium both during the charging process and the discharging process. When the temperature difference between the air at the inlet and outlet of the unit was positive, the PCM was being charged, and vice versa. A clear plastic tube was installed at roof level in the greenhouse to improve heated air movement into the PCM unit. Tables 1 and 2 describe air temperatures in the three greenhouses during the study. Fig. 1 illustrates sample temperature curves and daily diurnal temperature ranges that were narrow in the NT greenhouse and wider in the LT and PCM greenhouses. Mean daily temperatures (means of 96 readings per day) in both Table 1 Mean daily temperature and mean number of hours of daily temperatures 22 January through 26 May 1993 Greenhouse
Low night temperaturea Normal night temperatureb Phase change material”
Mean daily temperature
distribution
in three greenhouses from
( “C)
Below 8 ’ (h)
8-18” (h)
18-28” (h)
Above 28” (h)
7 0 1
8 8 7
6 13 8
3 3 2
Mean daily temperature “C
16.5 21.0 16.0
a 08 : 00- 17 : 00 h heat setting at 26” C, exhaust fans at 32” C, 17 : 00 to 08 : 00 h heat setting at 3 “C. b 08:00-17:00 h heat setting at 26°C exhaust fans at 32°C; 17:00-OS:00 h heat setting at 18°C. c Entire 24 h heat setting at 3”C, 08 :00-l 7 : 00 h exhaust fan setting at 35 “C. Heat supplied primarily by solar radiation and the phase change material energy storage module.
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Table 2 Mean monthly temperatures in three greenhouses from 22 January through 26 May 1993 Month
Jan Feb Mar Apr May
Greenhouse” Low night temperature (“C)
Normal night temperature (“C)
Phase change material (“C)
11 11 16 18 23
18 19 20 23 25
11 10 14 20 24
’ Treatments as in Table 1.
24
72 48 Time, h (O=OO:OO, 3/l 2/93)
96
120
Fig. 1. Temperature graphs of the phase change material energy storage unit greenhouse (PCM), normal night temperature greenhouse (NT), and low night temperature greenhouse (LT) from 12 to 17 March 1993.
the LT and PCM greenhouses were similar, about 5 ‘C lower than the NT greenhouse (Table 1). Air temperatures fluctuated much more in the PCM greenhouse than in the LT and NT greenhouses because of the heat and ventilation fan settings. The PCM greenhouse when compared with the LT greenhouse had, on average, 1 fewer h day- ’ in the range 8- 18oC, 2 h day- ’ more in the 18-28 ’ C range and 1 h day- ’ less above 28 ‘C even though they had similar mean daily temperatures. On a cloudy, cool day (shown in Fig. 1 between 24 and 48 h) the daytime temperature in the PCM greenhouse was much lower than in the other two greenhouses since no heat energy was added and there was minimal solar energy available for heating. The least amount of heat energy was added to the PCM green-
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311
house, the next highest amount to the LT greenhouse and the highest amount in the NT greenhouse (the actual amounts were not measured but were based on the periods of time the heating systems were in operation). Air temperatures were measured with shielded copper-constantan thermocouples attached to a Campbell 2 1X and also from shielded sensors transmitted to a Q-COM Gem II System. Photosynthetic photo flux density was measured by LI190SB quantum sensors attached and transmitted to the Q-COM system. A LICOR 3 100 was used to measure leaf area. Growth data were analyzed by using least significant differences to compare least square means. Seed for these studies was contributed by Ball (West Chicago, IL), Ernst Benary (Hann. Munden, Germany), Clause (San Juan Bautista, CA), Goldsmith (Gilroy, CA), and Sakata (Morgan Hill, CA). Plants (one per pot) were grown pot to pot with a border row to minimize edge effects and there were two replicates of live treatment plants each per greenhouse. Plants were visually matched at the beginning of each study so that similar crops were in each greenhouse. Footnotes in Tables 3-7 indicate the dates and the temperature regimes during the test period for each crop from first true leaf until three of the five test plants were in bloom at which point the top portions of all five plants were severed from the roots and numbers of leaves, lateral branches, flower buds and flowers were counted, leaf area measured and dry weight determined for each plant.
3. Results and Discussion 3.1. Gazania (Table 3) There were some statistically significant morphological changes in numbers of lateral branches, flowers and flower buds, and in main stem leaf area but none were of practical significance. There were no significant differences in plant height and numbers of main stem leaves. All plants bloomed in 9% 113 days. ‘Talent Yellow’ bloomed 10 days earlier in the PCM greenhouse than the in the LT. Crops grew well in all three greenhouses, but the LT greenhouse produced heavier plants with more leaf area. 3.2. Geranium (Table 4) ‘Red Elite’ as in previous studies, bloomed earlier when grown in a warm night greenhouse than in a colder night temperature greenhouse (Merritt and Kohl, 1989). There were no significant differences in plant height, numbers of lateral branches, flowers and flower buds. LT plants had smaller dry weights, but grew longer and had larger leaf areas than PCM or NT plants.
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324
318 Table 3 Morphological 1993’
characteristics
of gazania seedlings grown in three greenhouse temperature
regimes,
Cultivar
Greenhouse2
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm2)
Total top dry wt. (g)
‘Daybreak Garden Sun’
PCM NT LT
98 95 108
24” 23” 24”
1.4” 1.5” 1.5”
1136” 1034” 1633b
7.3” 8.3” 10.0”
‘Ministar White’
PCM NT LT
106 105 105
22” 26” 24”
1.0” 2.lb 0.6’
1480” 1369” 1614”
9.5a 10.0” 14.1”
‘Talent’ mix
PCM NT LT
105 103 109
26” 21” 26”
1.4p 1.7’ 1.4’
1402” 1545” 17918
9.9” 10.5” 10.8”
‘Talent Yellow’
PCM NT LT
103 105 113
24” 23” 24a
1.5” 1.2” 0.6”
1306” 1239” 1920b
8.1” 8.8” 9.6b
’ Values are means of ten plants; 100 pots me2; grown 22 January- 11 May, except ‘Talent Yellow’ 2 February-26 May. ’ PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 6 oC and mean daily temp. 15 aC, NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 mean minimum temp. 16°C and mean daily temp. 2 1 “C; LT, low night temperature greenhouse. From 17: 00 to 08 : 00 h mean minimum temp. 6°C and mean daily temp. 15 “C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PS 0.05).
3.3. Marigold, diploids: ‘Early Queen Sophia ’ and ‘Aurora Yellow’ (Table 5)
Plants bloomed 2-3 weeks earlier in the NT greenhouse and were shorter and smaller plants than those grown in the PCM and LT greenhouses. Plantsgrown in the PCM and LT greenhouses were very similar morphologically and bloomed in about the same number of days. There were no significant differences in numbers of main stem leaves, flowers and flower buds due to temperature treatment. 3.4. Marigold, triploids: ‘Zenith Yellow Crested’, ‘Mighty Marietta Orange’, ‘Spinner’ and ‘Yellow Nugget Supreme’ (Table 5)
All cultivars bloomed about 2 weeks earlier in the NT greenhouse and were generally shorter plants than those grown in the PCM and LT greenhouses which had similar bloom dates. There was some variability in plant morphology due to greenhouse environment. Total leaf area and plant dry weights varied considerably. Numbers of main stem leaves, branches and flowers were similar regardless
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324 Table 4 Morphological characteristis temperature regimes, 1993’ Crop and cultivar
Geranium ‘Red Elite’
Verbena ‘Imagination’
‘Rosy Red
Vinca ‘Little Blanche’
319
of geranium, verbena and vinca seedlings grown in three greenhouse
Greenhouse*
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm*)
Total top dry wt. (g)
PCM NT LT
99 91 108
28” 26a 29”
0.9” 0.9” 0.6”
1597ab 1337” 2056b
12” 20b 15ab
PCM NT LT PCM NT LT
68 56 68 15 68 77
23” 19” 21” 19” 15” 19”
0.9” 1.4= 1.0” 0.9” 1.1” 0.9”
783” 658” 930” 832” 665” 934”
3b
PCM NT LT
60 46 55
16” 17a 16”
0.9” 1.O” 0.6”
760” 828” 923”
;: 4” 3” 4a
1” 2” 2”
’ Values are means of ten plants; 100 pots m-’ except 59 me2 geraniums. Geranium grown 2 February-2 1 May; verbena 10 February-28 April, vinca 22 March-2 1 May. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7°C and mean daily temp. range 14- 16 “C except for vinca - minimum 12°C and mean daily 2 1 “C, NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 16 oC and mean daily temp. range 20-2 1” C, except vinca - minimum 19°C mean daily 23 “C, LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 7-8°C and mean daily temp. range 15-l 7°C except vinca - minimum 9”C, mean daily 19°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
of greenhouse environment. The number of ‘Spinner’ and ‘Zenith Yellow Crested flower buds were affected by temperature treatment, but the difference was only one or two buds. 3.5. Mmulus (Table 6) Plants bloomed earlier in the PCM and LT greenhouses than those grown in the NT greenhouses. Plants of each cultivar were morphologically similar regardless of greenhouse environment except for dry weight accumulation of the plants. Those grown in the PCM and LT greenhouses generally produced more dry weight per day than those grown at the higher night temperature (Merritt and Kohl, 1994).
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Table 5 Morphological characteristics 1993’
of marigold seedlings grown in three greenhouse temperature
regimes,
Cultivar
Greenhouse 2
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm’)
Total top dry wt. (g)
‘Aurora Yellow’
PCM NT LT
86 67 83
21b 19” 21s
1.5” l.lS 1.3”
1284” 1108” 1 192a
6.8” 5.1s 6.9”
‘Early Queen Sophia’
PCM NT LT
54 40 53
12s 8” 11s
0.9” 0.7” 0.7”
377” 285” 384”
1.48 1.0” 1.48
‘Mighty Marietta Orange’
PCM NT LT
50 37 46
11” 10” 10”
0.9” 1.0” 1.0”
251” 285” 200”
1.0” l.lS 0.8”
‘Spinner’
PCM NT LT
53 38 53
10s 8” 12b
0.9” 1.0” 1.2”
317” 311” 536b
1.2” 0.9s 2.4”
‘Yellow Nugget Supreme’
PCM NT LT
53 38 49
12b 9” 13s
0.9” 0.9” 0.8”
432” 444a 446”
1.8” 1.3” 1.8”
‘Zenith Yellow Crested
PCM NT LT
46 37 46
12” 12” 13”
0.6” 0.9” 0.8”
288” 493s 356ab
0.9” 1.4” 1.3”
’ Values are means of ten plants; 100 pots rne2; grown 12 February-l 1 April, except ‘Aurora’ 12 February-9 May. * PCM, phase change material energy storage unit greenhouse. From 17: 00 to 08 : 00 h mean minimum temp. range 4-7°C and mean daily temp. range 12-16°C; NT, high night temperature greenhouse. From 17: 00 to 08 :00 h mean minimum temp. range 15-16°C and mean daily temp. range 19-20°C; LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 mean minimum temp. range 7-8°C and mean daily temp. 15-17°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
3.6. Pansy (Table 7)
Plants bloomed 2-7 days earlier in the NT greenhouse than in the PCM and LT greenhouses. Plant characteristics at anthesis were very uniform in all three greenhouse environments. NT plant height, number of lateral branches and number of main stem leaves were similar. NT plants generally had less leaf area, except for the ‘Ultima’ cultivars. Plant quality and morphologic characteristics of
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324 Table 6 Morphological characteristics
of mimulus seedlings in three greenhouse temperature
321
regimes, 1993’
Cultivar
Greenhouse*
Days to bloom’
Height (cm)
Flowers (no.)
Total leaf area (cm’)
‘Calypso’ mix
PCM NT LT
45 61 46
25” 25” 26”
4.8” 5.3” 3.9”
1317” 1440” 1221”
4.9” 7.1S 8.0”
‘Mystic’ mix
PCM NT LT
42 60 46
9” 9” 9”
1.3” 2.9” 1.2”
824” 623” 920”
2.4” 2.0” 2.7”
‘Royal Velvet’
PCM NT LT
45 61 47
43” 29” 37”
4.1” 2.1” 1.0”
1886Ub 1548” 1904b
10.1” 9.4” 9.5”
‘Yellow Velvet’
PCM NT LT
45 62 47
35” 36” 32”
3.1” 8.4b 4.1*
1672” 1623” 1786”
9.2” 12.5” 9.8”
Total dry wt. (g)
’ Values are means of ten plants; 59 pots m-*; grown 1 March-28 April. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7°C and mean daily temp. 14-16°C; NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 16- 17 ’ C and mean daily temp. range 20-22 ’ C; LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 8-9 oC and mean daily temp. range 16-17°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
plants grown in the PCM greenhouse were comparable with, or better than, those grown with added heat energy, the LT and NT greenhouses. 3.7. Verbena (Table 4) There were no significant differences in plant height, numbers of leaves, lateral branches, flowers, and flower buds due to temperature treatments. Plants grew well in all three greenhouses. 3.8. Vinca (Table 4)
‘Little Blanche’ bloomed 9-14 days earlier in the NT greenhouse than in the PCM and LT greenhouses. They grew well in all three greenhouse environments. There were no statistical differences in any morphological characteristic evaluated due to variations in greenhouse temperatures. Height of the bedding plant species in this study did not respond to the higher day than night temperatures (positive DIF) temperatures in which they were
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Table 1 Morphological characteristics of pansy seedlings grown in three greenhouse temperature regimes, 1993’ Cultivar
Greenhouse 2
Days to bloom’
Height (cm)
Flowers (no.)
Total leaf area (cm’)
Total top dry wt. (g)
‘Accord Blue Blotch’
PCM NT LT
68 61 70
11” 11” 11”
0.7” 0.7” 0.6”
551ab 399” 672b
2.2” 1.9” 1.8”
‘Accord Yelow Blotch
PCM NT LT
69 63 74
17b 15ab 13”
0.9” 1.O” o.78
714ab 627” 877b
2.9” 2.7” 2.6”
‘Fama Red
PCM NT LT
68 62 69
12” 13” 12”
0.8” 1.5b 0.9”
708” 345b 763”
1.4a 1.6” 1.8”
‘Fama See Me’
PCM NT LT
68 61 66
15” 14a lgb
0.6” l.lb l.lb
554” 534” 875b
1.9” 1.9” 2.4b
‘Maxim Yellow’
PCM NT LT
69
61 68
12” 11’ 13”
l.lab 1.4b 1.0”
712’ 500” 808b
2.6” 2.0b 2.7a
‘Ultima Beacon Bicolor’
PCM NT LT
68 63 70
13” 12” 13”
811= 842” 883”
2.9” 3.0” 2.3b
‘Ultima Pink
PCM NT LT
67 65 68
10” 10”
435” 500” 509”
l.la 1.7b 1.4ab
9”
1.0” 1.9b 1.3”
’ Values are means of ten plants; 100 pots me2; grown 4 February- 19 April. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 5 ‘C and mean daily temp. range 13- 14°C; NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 15- 16°C and mean daily temp. 20” C, LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7 oC and mean daily temp. 15°C. ’ From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PS 0.05).
grown. Heins ( 1994) states that plant height response will be greater when positive DIF increases in magnitude, i.e. the larger the difference between day and night temperatures, the taller the plants. In this study, the LT DIF was about 2O”C, the NT DIF about 9°C and the PCM DIF variable, but close to the LT. In these studies, plant height response was statistically the same regardless of temperature (or DIF) for the gazania, geranium, verbena, vinca, mimulus and pansy
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323
cultivars. With marigold, there were either no height differences due to temperature or the NT (higher positive DIF) was shorter due to earlier formation of terminal flower buds. Compact, well branched crops having large numbers of flowers when grown at low temperatures (either LT or PCM) were obtained with the gazania cultivars, geranium ‘Red Elite’, all marigold cultivars except ‘Aurora Yellow’, mimulus ‘Mystic’, all pansy and verbena cultivars, and vinca ‘Little Blanche’. ‘Aurora Yellow’ marigold was the largest cultivar in the marigold study in terms of height and plant mass (leaf number and area, lateral branches and total top dry weight). Mimulus ‘Calypso’ mix, ‘Royal Velvet’ and ‘Yellow Velvet’ were tall, leggy but well branched. Mimulus is a photoperiodic plant (Merritt and Kohl, 1993 ) and much shorter flowering plants could have been obtained if seeding had been delayed until the longer natural photoperiods occurred or if day length had been extended by supplementary lighting. Crops evaluated which had no more than a 7 day delay in blooming in the LT and PCM greenhouses included gazania ‘Ministar White’, ‘Talent’ mix, pansy ‘Fama Red’, ‘Fama See Me’, ‘Ultima Beacon Bicolor’ and ‘Ultima Pink’. No pansy cultivars were delayed more than 11 days by the low temperatures and their growth and development response to the LT and PCM environments were almost identical regardless of cultivar. In general, the higher heat energy used in the NT and LT greenhouses did not produce morphologically different bedding plants when compared with those grown in the PCM greenhouse.
Acknowledgments
New Jersey Agricultural Experiment Station Paper No. D-03232-2-94. This work was supported by the Center for Controlled Environment in Agriculture and State of New Jersey funds.
References Giacomelli, G.A., Ting, KC., Wu, SW. and Yuan, Z.W., 1990. Plant growth within an enhanced environment greenhouse. Am. Sot. Agric. Eng. Paper 904531. ASAE, St. Joseph, MI. Heins, R.D., 1994. Plant growth and development responses to the cultural environment. Proceedings, Greenhouse Systems Automation, Culture and Environment International Conference, 2022 July 1994. NRAES, Ithaca, NY, 72, pp. 96-101. Hicklenton, P.R., Newman, S.M. and Davies. L.J., 1993a. Night temperature, photosynthetic photon flux, and long days affect Gypsophilapaniculata flowering. HortScience, 28: 888-890. Hicklenton, P.R., Newman, S.M. and Davies, L.J., 1993b. Growth and flowering of Gypsophilapanidata L. ‘Bristol Fairy’ and ‘Bridal Veil’ in relation to temperature and photosynthetic photo flux. Sci. Hortic., 53: 319-331. Lieth, J.H., Merritt, K.H. and Kohl, Jr., H.C., 1991. Crop productivity in relation to photosynthetically active radiation and air temperature. J. Am. Sot. Hortic. Sci., 116: 623-626.
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Merritt, R.H. and Kohl, Jr., H.C., 1989. Crop production and morphology of petunia and geranium in response to low night temperature. J. Am. Sot. Hortic. Sci., 114: 44-48. Merritt, R.H. and Kohl, Jr., H.C., 199 1. Morphology of bedding plants in response to low night temperature and energy use implications. Sci. Hortic., 45: 295-302. Merritt, R.H. and Kohl, Jr., H.C., 1994. Photoperiodic and temperature effects on growth and development of mimulus cultivars ‘Royal Velvet’ and ‘Yellow Velvet’. Sci. Hortic., in press. Merritt, R.H. and Ting, KC., 1994. Evaluation of an energy storage module as the primary heat source for greenhouse production of bedding plants. HortTechnology, in press. Ting, K.C., Giacomelli, G.A. and Wu, S.W., 1990. PCM energy storage for a CO2 enriched greenhouse. Am. Sot. Agric. Eng. Paper 904040. ASAE, St. Joseph, MI. Wu, S.W., 199 1. Environmental conditions and plant production within a PCM modulated, CO* and supplemental light enhanced greenhouse. MS Thesis, Rutgers Univ., New Brunswick, NJ.
Morphological responses of bedding plants to three greenhouse temperature regimes Richard H. Merritt”,*, KC. Tingb =Departmentof Plant Science, New Jersey Agricultural Experiment Station, Rutgers University,New Brunswick, NJ 08903, USA bDepartment of Bioresource Engineering, New Jersey Agricultural Experiment Station, Rutgers University,New Brunswick, NJ 08903, USA
Accepted 2 August 1994
Abstract Seedling crops of gazania, geranium, marigold, mimulus, pansy, verbena and vinca were grown to 60% anthesis in three greenhouse temperature regimes: (a) 26°C day/6 k 3°C night (LT),witha 16.5”Cmeandailytemperature (MDT), (b) 26”Cday/l7+4”Cnight,
with a 2 1“C MDT, and (c) variable day/night temperatures in response to heating and cooling by a phase change material energy storage module (PCM) with an 8 If:2’ C night and a 16oC MDT. Crops bloomed from 2 to 17 days earlier in the 26”C/ 17 ” C greenhouse. The morphological characteristics of all cultivars of gazania, mimulus, pansy and verbena, geranium and vinca were similar regardless of greenhouse temperature regime. Marigold diploid and triploid cultivars and mimulus were morphologically more variable than the other bedding plant species. Crops grown in the PCM and LT greenhouses had virtually identical morphological characteristics and bloomed in about the same number of days. Plant height was not affected by DIF environments in the greenhouses. The PCM and LT greenhouses had a similar MDT, but the distribution of numbers of hours of mean daily temperatures was different. Keywords: Energy conservation; Flowering; Gazania (Gazania splendens); Geranium (Pelarganium x hortorum); Height; Low night temperatures; Marigold (Tagetes patula and Tagetes erectaxpatula); Mimulus (Mimulusx hydrides); Pansy ( Violax Wittrockiana);Phase change material energy storage unit; Verbena ( Verbenax hybrida); Vinca (Catharanthus roseus)
* Corresponding author. 03044238/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
SSDIO304-4238(94)00714-4
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R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324
1. Introduction Research studies have evaluated energy conservation approaches and their effect on growth and development of several bedding plant crops (Merritt and Kohl, 199 1; Lieth et al., 199 1). The goals of this research were ( 1) to identify bedding plants that will grow to be compact, well branched and to have large numbers of flowers when grown at low ambient temperatures normally associated with spring bedding plant production in New Jersey, (2) to identify plant germplasm that will have minimal or no delay in blooming when grown at low temperatures and (3 ) to minimize heat energy costs. Morphological characteristics of bedding plants when the crop was at 60% anthesis were evaluated in response to three greenhouse temperature regimes, two of which focused on minimizing fossil fuel use either by low night temperature or by substituting a phase change material energy storage module (PCM) designed to collect and store solar energy during the day and to release heat energy at night (Giacomelli et al., 1990; Ting et al., 1990; Wu, 199 1). Another objective was to evaluate crop growth and development responses to greenhouse temperatures which could vary greatly due to the PCM operation. Studies with marigold, pansy, petunia and verbena have shown that they can be grown with desirable morphological characteristics at low night temperatures with reduced heat energy costs and with minimal delay in blooming (Merritt and Kohl, 1989, 199 1). Temperature and light may also affect growth and flowering of baby’s breath. Night temperatures below 8 “C and a low photosynthetic photo flux affected anthesis of one cultivar but not another, indicating cultivar variation in response to temperature (Hicklenton et al., 1993a,b).
2. Materials and methods Visually matched crops of gazania (Gazania splendens, cultivars ‘Ministar White’, ‘Daybreak Garden Sun’, ‘Talent Yellow’, ‘Talent’ mix), geranium (Pelarganiumx hurtorumcultivar ‘Red Elite’), marigold ( Tagetespatula,cultivars ‘Early Queen Sophia’, ‘Aurora Yellow’), (Tagetes erectaxpatula, cultivars ‘Spinner’, ‘Zenith Yellow Crested’, ‘Mighty Marietta Orange’, ‘Yellow Nugget Supreme’), mimulus (Mimulusx hydridus, cultivars ‘Royal Velvet’, ‘Yellow Velvet’, ‘Calypso’ Mix, ‘Mystic’ Mix), pansy ( Viulax Wittrockianacultivars ‘Accord Yellow Blotch’, ‘Accord Blue Blotch’, ‘Ultima Pink’, ‘Ultima Beacon Bicolor’, ‘Maxim Yellow’, ‘Fama See Me’, ‘Fama Red’), verbena ( Verbenax hybrida cultivars ‘Imagination’, ‘Rosy Red’), and vinca (Catharanthus ruseus cultivar ‘Little Blanche’) were selected at first true leaf stage and grown until 60% of the crop had reached anthesis. Research was conducted 22 January to 26 May 1993 in three adjacent air-inflated double polyethylene (colorless 6 mil Nutrogro by Visgreen plastic) greenhouses, each 8.5 mx 14.6 m, oriented N-S. The low night temperature greenhouse (LT) had heat added when the air temperature dropped below 26 “C during the daytime hours of 08 : 00- 17 : 00. Exhaust fans were set at
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315
32 “C. From 17 : 00 to 08 : 00 h no heat was added until the temperature reached 3 “C. The higher night temperature greenhouse (NT) had the same daytime heat and exhaust fan settings as the LT greenhouse. The 17 : 00-08 : 00 heat setting was 18’ C. The phase change module greenhouse (PCM) was not heated during the entire 24 h period unless the temperature went below 3 “C. Exhaust fans were set at 35 “C. The heating and venting temperature targets were usually attained, but on very sunny or cold windy days the heat and ventilation systems often did not provide the heat or cooling necessary to meet the temperature targets. Solar energy collected and stored for later release by the PCM provided most of the heat for the PCM greenhouse. The phase change material was Glauber’s salt (Na,SO,* 1OH20), sodium carbonate decahydrate ( Na2C03* 1OH20), nucleating and stabilizing agents. The mixture had a design phase change temperature of 16‘C to enable the PCM to collect and store solar energy during daytime hours and to release this heat energy to the greenhouse during night-time hours (Merritt and Ting, 1994). Previous studies (Giacomelli et al., 1990; Wu, 199 1) have evaluated plant growth in PCM-heated and -cooled greenhouses. The PCM unit contained 660 kg of phase change material packaged in 44 tube-sheets in a design similar to the unit described in Ting et al. ( 1990). A 250 W fan (Dayton Venture) (0.25 KWH h- ’ ) was installed and operated continuously to provide an airflow of 1.274 m3 s-’ through the unit. The operation of the fan motor increased air temperature in the PCM greenhouse by about 0.2”C. Air served as the energy carrying medium both during the charging process and the discharging process. When the temperature difference between the air at the inlet and outlet of the unit was positive, the PCM was being charged, and vice versa. A clear plastic tube was installed at roof level in the greenhouse to improve heated air movement into the PCM unit. Tables 1 and 2 describe air temperatures in the three greenhouses during the study. Fig. 1 illustrates sample temperature curves and daily diurnal temperature ranges that were narrow in the NT greenhouse and wider in the LT and PCM greenhouses. Mean daily temperatures (means of 96 readings per day) in both Table 1 Mean daily temperature and mean number of hours of daily temperatures 22 January through 26 May 1993 Greenhouse
Low night temperaturea Normal night temperatureb Phase change material”
Mean daily temperature
distribution
in three greenhouses from
( “C)
Below 8 ’ (h)
8-18” (h)
18-28” (h)
Above 28” (h)
7 0 1
8 8 7
6 13 8
3 3 2
Mean daily temperature “C
16.5 21.0 16.0
a 08 : 00- 17 : 00 h heat setting at 26” C, exhaust fans at 32” C, 17 : 00 to 08 : 00 h heat setting at 3 “C. b 08:00-17:00 h heat setting at 26°C exhaust fans at 32°C; 17:00-OS:00 h heat setting at 18°C. c Entire 24 h heat setting at 3”C, 08 :00-l 7 : 00 h exhaust fan setting at 35 “C. Heat supplied primarily by solar radiation and the phase change material energy storage module.
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R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324
Table 2 Mean monthly temperatures in three greenhouses from 22 January through 26 May 1993 Month
Jan Feb Mar Apr May
Greenhouse” Low night temperature (“C)
Normal night temperature (“C)
Phase change material (“C)
11 11 16 18 23
18 19 20 23 25
11 10 14 20 24
’ Treatments as in Table 1.
24
72 48 Time, h (O=OO:OO, 3/l 2/93)
96
120
Fig. 1. Temperature graphs of the phase change material energy storage unit greenhouse (PCM), normal night temperature greenhouse (NT), and low night temperature greenhouse (LT) from 12 to 17 March 1993.
the LT and PCM greenhouses were similar, about 5 ‘C lower than the NT greenhouse (Table 1). Air temperatures fluctuated much more in the PCM greenhouse than in the LT and NT greenhouses because of the heat and ventilation fan settings. The PCM greenhouse when compared with the LT greenhouse had, on average, 1 fewer h day- ’ in the range 8- 18oC, 2 h day- ’ more in the 18-28 ’ C range and 1 h day- ’ less above 28 ‘C even though they had similar mean daily temperatures. On a cloudy, cool day (shown in Fig. 1 between 24 and 48 h) the daytime temperature in the PCM greenhouse was much lower than in the other two greenhouses since no heat energy was added and there was minimal solar energy available for heating. The least amount of heat energy was added to the PCM green-
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311
house, the next highest amount to the LT greenhouse and the highest amount in the NT greenhouse (the actual amounts were not measured but were based on the periods of time the heating systems were in operation). Air temperatures were measured with shielded copper-constantan thermocouples attached to a Campbell 2 1X and also from shielded sensors transmitted to a Q-COM Gem II System. Photosynthetic photo flux density was measured by LI190SB quantum sensors attached and transmitted to the Q-COM system. A LICOR 3 100 was used to measure leaf area. Growth data were analyzed by using least significant differences to compare least square means. Seed for these studies was contributed by Ball (West Chicago, IL), Ernst Benary (Hann. Munden, Germany), Clause (San Juan Bautista, CA), Goldsmith (Gilroy, CA), and Sakata (Morgan Hill, CA). Plants (one per pot) were grown pot to pot with a border row to minimize edge effects and there were two replicates of live treatment plants each per greenhouse. Plants were visually matched at the beginning of each study so that similar crops were in each greenhouse. Footnotes in Tables 3-7 indicate the dates and the temperature regimes during the test period for each crop from first true leaf until three of the five test plants were in bloom at which point the top portions of all five plants were severed from the roots and numbers of leaves, lateral branches, flower buds and flowers were counted, leaf area measured and dry weight determined for each plant.
3. Results and Discussion 3.1. Gazania (Table 3) There were some statistically significant morphological changes in numbers of lateral branches, flowers and flower buds, and in main stem leaf area but none were of practical significance. There were no significant differences in plant height and numbers of main stem leaves. All plants bloomed in 9% 113 days. ‘Talent Yellow’ bloomed 10 days earlier in the PCM greenhouse than the in the LT. Crops grew well in all three greenhouses, but the LT greenhouse produced heavier plants with more leaf area. 3.2. Geranium (Table 4) ‘Red Elite’ as in previous studies, bloomed earlier when grown in a warm night greenhouse than in a colder night temperature greenhouse (Merritt and Kohl, 1989). There were no significant differences in plant height, numbers of lateral branches, flowers and flower buds. LT plants had smaller dry weights, but grew longer and had larger leaf areas than PCM or NT plants.
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324
318 Table 3 Morphological 1993’
characteristics
of gazania seedlings grown in three greenhouse temperature
regimes,
Cultivar
Greenhouse2
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm2)
Total top dry wt. (g)
‘Daybreak Garden Sun’
PCM NT LT
98 95 108
24” 23” 24”
1.4” 1.5” 1.5”
1136” 1034” 1633b
7.3” 8.3” 10.0”
‘Ministar White’
PCM NT LT
106 105 105
22” 26” 24”
1.0” 2.lb 0.6’
1480” 1369” 1614”
9.5a 10.0” 14.1”
‘Talent’ mix
PCM NT LT
105 103 109
26” 21” 26”
1.4p 1.7’ 1.4’
1402” 1545” 17918
9.9” 10.5” 10.8”
‘Talent Yellow’
PCM NT LT
103 105 113
24” 23” 24a
1.5” 1.2” 0.6”
1306” 1239” 1920b
8.1” 8.8” 9.6b
’ Values are means of ten plants; 100 pots me2; grown 22 January- 11 May, except ‘Talent Yellow’ 2 February-26 May. ’ PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 6 oC and mean daily temp. 15 aC, NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 mean minimum temp. 16°C and mean daily temp. 2 1 “C; LT, low night temperature greenhouse. From 17: 00 to 08 : 00 h mean minimum temp. 6°C and mean daily temp. 15 “C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PS 0.05).
3.3. Marigold, diploids: ‘Early Queen Sophia ’ and ‘Aurora Yellow’ (Table 5)
Plants bloomed 2-3 weeks earlier in the NT greenhouse and were shorter and smaller plants than those grown in the PCM and LT greenhouses. Plantsgrown in the PCM and LT greenhouses were very similar morphologically and bloomed in about the same number of days. There were no significant differences in numbers of main stem leaves, flowers and flower buds due to temperature treatment. 3.4. Marigold, triploids: ‘Zenith Yellow Crested’, ‘Mighty Marietta Orange’, ‘Spinner’ and ‘Yellow Nugget Supreme’ (Table 5)
All cultivars bloomed about 2 weeks earlier in the NT greenhouse and were generally shorter plants than those grown in the PCM and LT greenhouses which had similar bloom dates. There was some variability in plant morphology due to greenhouse environment. Total leaf area and plant dry weights varied considerably. Numbers of main stem leaves, branches and flowers were similar regardless
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324 Table 4 Morphological characteristis temperature regimes, 1993’ Crop and cultivar
Geranium ‘Red Elite’
Verbena ‘Imagination’
‘Rosy Red
Vinca ‘Little Blanche’
319
of geranium, verbena and vinca seedlings grown in three greenhouse
Greenhouse*
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm*)
Total top dry wt. (g)
PCM NT LT
99 91 108
28” 26a 29”
0.9” 0.9” 0.6”
1597ab 1337” 2056b
12” 20b 15ab
PCM NT LT PCM NT LT
68 56 68 15 68 77
23” 19” 21” 19” 15” 19”
0.9” 1.4= 1.0” 0.9” 1.1” 0.9”
783” 658” 930” 832” 665” 934”
3b
PCM NT LT
60 46 55
16” 17a 16”
0.9” 1.O” 0.6”
760” 828” 923”
;: 4” 3” 4a
1” 2” 2”
’ Values are means of ten plants; 100 pots m-’ except 59 me2 geraniums. Geranium grown 2 February-2 1 May; verbena 10 February-28 April, vinca 22 March-2 1 May. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7°C and mean daily temp. range 14- 16 “C except for vinca - minimum 12°C and mean daily 2 1 “C, NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 16 oC and mean daily temp. range 20-2 1” C, except vinca - minimum 19°C mean daily 23 “C, LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 7-8°C and mean daily temp. range 15-l 7°C except vinca - minimum 9”C, mean daily 19°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
of greenhouse environment. The number of ‘Spinner’ and ‘Zenith Yellow Crested flower buds were affected by temperature treatment, but the difference was only one or two buds. 3.5. Mmulus (Table 6) Plants bloomed earlier in the PCM and LT greenhouses than those grown in the NT greenhouses. Plants of each cultivar were morphologically similar regardless of greenhouse environment except for dry weight accumulation of the plants. Those grown in the PCM and LT greenhouses generally produced more dry weight per day than those grown at the higher night temperature (Merritt and Kohl, 1994).
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Table 5 Morphological characteristics 1993’
of marigold seedlings grown in three greenhouse temperature
regimes,
Cultivar
Greenhouse 2
Days to bloom3
Height (cm)
Flowers (no.)
Total leaf area (cm’)
Total top dry wt. (g)
‘Aurora Yellow’
PCM NT LT
86 67 83
21b 19” 21s
1.5” l.lS 1.3”
1284” 1108” 1 192a
6.8” 5.1s 6.9”
‘Early Queen Sophia’
PCM NT LT
54 40 53
12s 8” 11s
0.9” 0.7” 0.7”
377” 285” 384”
1.48 1.0” 1.48
‘Mighty Marietta Orange’
PCM NT LT
50 37 46
11” 10” 10”
0.9” 1.0” 1.0”
251” 285” 200”
1.0” l.lS 0.8”
‘Spinner’
PCM NT LT
53 38 53
10s 8” 12b
0.9” 1.0” 1.2”
317” 311” 536b
1.2” 0.9s 2.4”
‘Yellow Nugget Supreme’
PCM NT LT
53 38 49
12b 9” 13s
0.9” 0.9” 0.8”
432” 444a 446”
1.8” 1.3” 1.8”
‘Zenith Yellow Crested
PCM NT LT
46 37 46
12” 12” 13”
0.6” 0.9” 0.8”
288” 493s 356ab
0.9” 1.4” 1.3”
’ Values are means of ten plants; 100 pots rne2; grown 12 February-l 1 April, except ‘Aurora’ 12 February-9 May. * PCM, phase change material energy storage unit greenhouse. From 17: 00 to 08 : 00 h mean minimum temp. range 4-7°C and mean daily temp. range 12-16°C; NT, high night temperature greenhouse. From 17: 00 to 08 :00 h mean minimum temp. range 15-16°C and mean daily temp. range 19-20°C; LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 mean minimum temp. range 7-8°C and mean daily temp. 15-17°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
3.6. Pansy (Table 7)
Plants bloomed 2-7 days earlier in the NT greenhouse than in the PCM and LT greenhouses. Plant characteristics at anthesis were very uniform in all three greenhouse environments. NT plant height, number of lateral branches and number of main stem leaves were similar. NT plants generally had less leaf area, except for the ‘Ultima’ cultivars. Plant quality and morphologic characteristics of
R.H. Merritt, K.C. Ting /Scientia Horticulturae 60 (1995) 313-324 Table 6 Morphological characteristics
of mimulus seedlings in three greenhouse temperature
321
regimes, 1993’
Cultivar
Greenhouse*
Days to bloom’
Height (cm)
Flowers (no.)
Total leaf area (cm’)
‘Calypso’ mix
PCM NT LT
45 61 46
25” 25” 26”
4.8” 5.3” 3.9”
1317” 1440” 1221”
4.9” 7.1S 8.0”
‘Mystic’ mix
PCM NT LT
42 60 46
9” 9” 9”
1.3” 2.9” 1.2”
824” 623” 920”
2.4” 2.0” 2.7”
‘Royal Velvet’
PCM NT LT
45 61 47
43” 29” 37”
4.1” 2.1” 1.0”
1886Ub 1548” 1904b
10.1” 9.4” 9.5”
‘Yellow Velvet’
PCM NT LT
45 62 47
35” 36” 32”
3.1” 8.4b 4.1*
1672” 1623” 1786”
9.2” 12.5” 9.8”
Total dry wt. (g)
’ Values are means of ten plants; 59 pots m-*; grown 1 March-28 April. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7°C and mean daily temp. 14-16°C; NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 16- 17 ’ C and mean daily temp. range 20-22 ’ C; LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 8-9 oC and mean daily temp. range 16-17°C. 3 From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PI 0.05 ) .
plants grown in the PCM greenhouse were comparable with, or better than, those grown with added heat energy, the LT and NT greenhouses. 3.7. Verbena (Table 4) There were no significant differences in plant height, numbers of leaves, lateral branches, flowers, and flower buds due to temperature treatments. Plants grew well in all three greenhouses. 3.8. Vinca (Table 4)
‘Little Blanche’ bloomed 9-14 days earlier in the NT greenhouse than in the PCM and LT greenhouses. They grew well in all three greenhouse environments. There were no statistical differences in any morphological characteristic evaluated due to variations in greenhouse temperatures. Height of the bedding plant species in this study did not respond to the higher day than night temperatures (positive DIF) temperatures in which they were
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Table 1 Morphological characteristics of pansy seedlings grown in three greenhouse temperature regimes, 1993’ Cultivar
Greenhouse 2
Days to bloom’
Height (cm)
Flowers (no.)
Total leaf area (cm’)
Total top dry wt. (g)
‘Accord Blue Blotch’
PCM NT LT
68 61 70
11” 11” 11”
0.7” 0.7” 0.6”
551ab 399” 672b
2.2” 1.9” 1.8”
‘Accord Yelow Blotch
PCM NT LT
69 63 74
17b 15ab 13”
0.9” 1.O” o.78
714ab 627” 877b
2.9” 2.7” 2.6”
‘Fama Red
PCM NT LT
68 62 69
12” 13” 12”
0.8” 1.5b 0.9”
708” 345b 763”
1.4a 1.6” 1.8”
‘Fama See Me’
PCM NT LT
68 61 66
15” 14a lgb
0.6” l.lb l.lb
554” 534” 875b
1.9” 1.9” 2.4b
‘Maxim Yellow’
PCM NT LT
69
61 68
12” 11’ 13”
l.lab 1.4b 1.0”
712’ 500” 808b
2.6” 2.0b 2.7a
‘Ultima Beacon Bicolor’
PCM NT LT
68 63 70
13” 12” 13”
811= 842” 883”
2.9” 3.0” 2.3b
‘Ultima Pink
PCM NT LT
67 65 68
10” 10”
435” 500” 509”
l.la 1.7b 1.4ab
9”
1.0” 1.9b 1.3”
’ Values are means of ten plants; 100 pots me2; grown 4 February- 19 April. 2 PCM, phase change material energy storage unit greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 5 ‘C and mean daily temp. range 13- 14°C; NT, high night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. 15- 16°C and mean daily temp. 20” C, LT, low night temperature greenhouse. From 17 : 00 to 08 : 00 h mean minimum temp. range 6-7 oC and mean daily temp. 15°C. ’ From first true leaf to 60% anthesis. Comparisons by greenhouse within a cultivar using least significant differences to compare least square means. Means with a letter in common are not significantly different (PS 0.05).
grown. Heins ( 1994) states that plant height response will be greater when positive DIF increases in magnitude, i.e. the larger the difference between day and night temperatures, the taller the plants. In this study, the LT DIF was about 2O”C, the NT DIF about 9°C and the PCM DIF variable, but close to the LT. In these studies, plant height response was statistically the same regardless of temperature (or DIF) for the gazania, geranium, verbena, vinca, mimulus and pansy
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323
cultivars. With marigold, there were either no height differences due to temperature or the NT (higher positive DIF) was shorter due to earlier formation of terminal flower buds. Compact, well branched crops having large numbers of flowers when grown at low temperatures (either LT or PCM) were obtained with the gazania cultivars, geranium ‘Red Elite’, all marigold cultivars except ‘Aurora Yellow’, mimulus ‘Mystic’, all pansy and verbena cultivars, and vinca ‘Little Blanche’. ‘Aurora Yellow’ marigold was the largest cultivar in the marigold study in terms of height and plant mass (leaf number and area, lateral branches and total top dry weight). Mimulus ‘Calypso’ mix, ‘Royal Velvet’ and ‘Yellow Velvet’ were tall, leggy but well branched. Mimulus is a photoperiodic plant (Merritt and Kohl, 1993 ) and much shorter flowering plants could have been obtained if seeding had been delayed until the longer natural photoperiods occurred or if day length had been extended by supplementary lighting. Crops evaluated which had no more than a 7 day delay in blooming in the LT and PCM greenhouses included gazania ‘Ministar White’, ‘Talent’ mix, pansy ‘Fama Red’, ‘Fama See Me’, ‘Ultima Beacon Bicolor’ and ‘Ultima Pink’. No pansy cultivars were delayed more than 11 days by the low temperatures and their growth and development response to the LT and PCM environments were almost identical regardless of cultivar. In general, the higher heat energy used in the NT and LT greenhouses did not produce morphologically different bedding plants when compared with those grown in the PCM greenhouse.
Acknowledgments
New Jersey Agricultural Experiment Station Paper No. D-03232-2-94. This work was supported by the Center for Controlled Environment in Agriculture and State of New Jersey funds.
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Merritt, R.H. and Kohl, Jr., H.C., 1989. Crop production and morphology of petunia and geranium in response to low night temperature. J. Am. Sot. Hortic. Sci., 114: 44-48. Merritt, R.H. and Kohl, Jr., H.C., 199 1. Morphology of bedding plants in response to low night temperature and energy use implications. Sci. Hortic., 45: 295-302. Merritt, R.H. and Kohl, Jr., H.C., 1994. Photoperiodic and temperature effects on growth and development of mimulus cultivars ‘Royal Velvet’ and ‘Yellow Velvet’. Sci. Hortic., in press. Merritt, R.H. and Ting, KC., 1994. Evaluation of an energy storage module as the primary heat source for greenhouse production of bedding plants. HortTechnology, in press. Ting, K.C., Giacomelli, G.A. and Wu, S.W., 1990. PCM energy storage for a CO2 enriched greenhouse. Am. Sot. Agric. Eng. Paper 904040. ASAE, St. Joseph, MI. Wu, S.W., 199 1. Environmental conditions and plant production within a PCM modulated, CO* and supplemental light enhanced greenhouse. MS Thesis, Rutgers Univ., New Brunswick, NJ.