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Morphology of bedding plants in response to low night temperature and energy use implications
Scientia Horticulturae, 45 ( 1991 ) 2 9 5 - 3 0 2
295
Elsevier Science Publishers B.V., A m s t e r d a m
Morphology of bedding plants in response to low night temperature and energy use implications Richard H. Merritt and Harry C. Kohl, Jr.* Department of Horticulture, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903 (U.S.A.) (Accepted for publication 7 May 1990)
ABSTRACT Merritt, R.H. and Kohl, H.C., Jr., 1991. Morphology of bedding plants in response t o l o w night temperature and energy use implications. Scientia Hortic., 45: 295-302. Seedlings of bedding plant crops were grown in greenhouses, January-May 1987 and 1989, at day air temperatures of 27 + 3 ° C (9 h) and either 7 + 3 ° C or 18 + 3 ° C night air temperatures ( 15 h). Morphological evaluations of the crop response to night temperatures were taken and calculations of fuel energy required to operate greenhouses at 7 and 18 ° C were determined. Crops which grew well at 7°C and which were short, compact and bloomed quickly were mimulus (cultivar 'Yellow Flower'), marigold (cultivars "Aurora', 'Janie') and petunia (cultivars 'Crimson', 'Joy'). Other crops which grew well at 7°C, but took longer to bloom were geranium (cultivars 'Cardinal Orbit', 'Orbit Glow', 'Pink Elite', 'Violet Elite'), marigold (cultivar 'Perfection'), pansy (cultivar cultivar 'Universal Mix') and verbena (cultivar 'Springtime' ). Crops which were stunted or took too long to bloom were impatiens (cultivar 'Accent'), dianthus (cultivars 'Big Eye Crimson' and 'Scarlet', 'Magic Charm', 'Princess' ), snapdragon (cultivars 'Liberty', 'Pixie' ) and zinnia (cultivar 'Peter Pan' ). Fuel savings at 7 vs. 18°C were 9.7 1 of fuel oil per square meter in January, 8.8 in February, 9.6 in March and 1.8 in April. Keywords: Antirrhinum majus; bedding plants; Dianthus chinensis; fuel energy requirements; Impatiens holsti; Mimulus hybridus; Pelargonium × hortorum; Petunia hybrida; Tagetes patula; temperature; Verbena hortensis; Viola tricolor, Zinnia elegans. AbbreviatiOns: LAI = leaf area m - 2 surface; WNT = warm night temperature; LNT = low night temperature; PPF = photosynthetic photon flux.
INTRODUCTION
Greenhouse production of bedding plants for spring sales in northern latitudes may be adversely affected by low light intensities (photosynthetic photon flux, PPF) and high fuel costs to heat greenhouses in January through April. Cultivar "Snow Cloud' petunias grown in greenhouses (Merritt and *Present address: California Agricultural E x p e r i m e n t a l Station, Davis, CA 95616, U.S.A.
0304-4238/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
296
R.H. MERRITT AND H.C. KOHL, JR.
Kohl, 1989 ) held at day temperatures of 21 and 27 ° C, respectively, and 7 ° C night temperatures had more basal branches and were one-third the height of those grown at a 27 ° C day and 18 ° C night temperature. Anthesis was delayed 10 days at the 7 °C night temperature. Cultivars 'Red Elite' and 'Cardinal Orbit' geraniums grown at 27 ° C day and either 7 or 18 ° C night temperature had a growth response similar to petunia, but the 7 ° C crop was much shorter and more compact than those grown at 18 ° C and anthesis was delayed 3 weeks. These studies also supported the hypothesis that at low PPF, geranium and petunia can produce dry matter per square meter with equal efficiency under both normal and low night temperatures when the plant canopy is closed to trap the available light, and when the plants are not sink limited, i.e. have many lateral branches (Merritt and Kohl, 1983; Shedlosky and White, 1987 ). The studies reported here were designed to determine whether or not other commercially important bedding plant crops can successfully be grown at low night temperatures and low PPF. Plant characteristics, dry matter production and fuel costs to produce crops to anthesis were considered. MATERIALSAND METHODS Crops selected for evaluation in 1987 and 1989 are listed in Table 1. Seeds of all crops (Goldsmith Seeds, Gilroy, CA) were sown on 8 January 1987 and 4 January 1989, except geranium on 16 January, in New Brunswick, NJ. Seedlings were grown at a m i n i m u m 21 ° C day/18 ° C night air temperatures on porous concrete benches that maintained the medium at 24-26 ° C. In 1987, geranium seedlings were transplanted on 29 January into 13-cm square plastic pots, impatiens were transplanted on 23 January, and petunias and marigolds on 28 January, all into 10-cm square plastic pots. In 1989, seedling transplanting for marigolds was on 17 January, dianthus on 20 January, mimulus, pansy, snapdragon, verbena and zinnia on 25 January, and geranium on 6 February. Mimulus, pansy, zinnia and geranium were transplanted into 10-cm square plastic pots; dianthus, marigold, snapdragon and verbena into 5-cm square plastic pots. In both years, plants from each bedding plant cultivar were visually matched into groups to achieve visually identical treatment blocks (Merritt and Kohl, 1989 ). Differential temperature treatments began within 1 week after transplanting. In 1987, pot-to-pot spacing was maintained throughout the experiments and there was one replicate of four plants for each crop in each greenhouse. In 1989, pot-to-pot spacing was maintained until plant canopy closure, at which time the pots were respaced as described in Table 1. Two replicates of five plants each for each crop were placed in both the 7 and 18 ° C greenhouses. To minimize edge effects, pots with seedlings of comparable size were used to form two border rows on all sides of each treatment. In 1987, growth data were taken when the 18°C crop was 50% in bloom (Table 2). The 7°C
RESPONSE OF BEDDING PLANTS TO LOW NIGHT TEMPERATURE
297
TABLE1 The influence of two night temperatures ( 15 h each night) on anthesis of bedding plants grown in the greenhouse, January through May, 1987 and 1989. The n u m b e r of days is from the first true leaf stage of growth to anthesis. Anthesis in 1987 was the date when the 18 °C crop had one-half the plants in flower. It is a same-day comparison between the 18 and 7°C crops. In 1989, anthesis was when both the 18 and 7 ° C crops were 50% in flower. Leaf area index ( LAI ) = leaf area m - 2 surface Year/crop
Cultivar
Night temperature ( ° C)
1987 Geranium
('Orbit Glow')
7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18
88 68 88 67 88 68 89 35 31 21 60 39 51 43 55 43
59 59 59 59 59 59 100 100 100 100 100 100 100 100 100 100
4.0 8.3 4.1 7.7 3.5 7.4 0.4 5.2 2.1 5.4 3.6 5.8 7.5 8.6 7.1 7.3
7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18
92 68 98 63 96 70 83 60 99 74 42 27 33 26 68 68 61 46 102 57 80 56 70 56 109 41
162 167 159 175 149 152 146 146 57 52 217 241 275 250 97 97 97 84 149 148 158 148 167 166 97 66
6.6 5.4 6.7 4.4 7.4 6.1 9.0 7.6 3.2 7.6 0.4 0.9 0.4 0.7 3.9 2.9 1.0 1.1 10.1 5.3 6.9 5.7 2.8 3.6 1.8 0.5
('Pink elite' ) ('Violet elite') Impatiens
('Accent')
Marigold
('Aurora') ('Perfection')
Petunia
('Crimson') ('Joy')
1989 Dianthus
('Big Eye Crimson') ('Big Eye Scarlet') ('Magic Charm' ) ('Princess')
Geranium
('Cardinal Orbit')
Marigold
('Aurora') ('Janie')
Mimulus
('Yellow Flower')
Pansy
('Universal Mix')
Snapdragon
( 'Liberty' ) ('Pixie')
Verbena
('Springtime')
Zinnia
('Peter Pan' )
No. of days from start of experiment to anthesis
Final spacing of pots m -2
LAI at anthesis
('Joy')
Petunia ('Crimson')
('Perfection')
Marigold ('Aurora')
7 t8
7 18
7 18
7 18
14 31
14 27
18 22
12 15
5 22
7
15 34
15 31
16 39
Plant height (cm)
18
7 18
('Violet elite')
Impatiens ('Accent')
7 18
7 18
Night temperature (°C)
('Pink elite')
Geranium ('Orbit Glow')
Crop
9 24
10 19
14 17
8 11
18
3
6 11
6 13
6 13
Length of main stem (cm)
20NS 20
17NS 18
16NS 17
11NS 14
-
-
13 17
12NS 14
13NS 14
No. of main stem leaves
320 233
320 168
-
-
-
322 762
376 528
519 854
Main stem leaf area (cm 2)
1090 727
745NS 858
362 581
214 547
38 516
591 1253
698 1297
678 1409
Total leaf area (cm 2)
14 11
11 9
-
-
8 11
llNS 11
11NS 11
10NS 8
No. of lateral shoots
2.9NS 3.1
3.5NS 3.0
2.2NS 2.8
1.4 2.6
0.2 2.0
4.1 7.3
4.9 7.3
4.6 7.8
Top dry weight (g)
6 April 25 March
3 April 25 March
6 April 17 March
9 March 26 February
1 May 12 March
4May 14 April
4 May 13 April
4 May 14 April
Date of anthesis
Theinfluence of two night temperatures (15 h each night) on the growth characteristics of seedlings grown in greenhouses in 1987. Growth data expressed as means; n = 4 plants. All data pairs except those indicated NS are significantly different at ~he < 5% level due to temperature treatment as determined by F-test
TABLE 2
~7
tO
Zinnia ('Peter Pan' )
Verbena ('Springtime')
('Liberty')
Snapdragon ( 'Pixie' )
Pansy ('Universal Mix' )
Mimulus ( 'Yellow Flower' )
('Janie')
Marigold ('Aurora')
Geranium ('Cardinal Orbit' )
('Princess')
('Magic Charm' )
('Big Eye Scarlet' )
Dianthus ('Big Eye Crimson')
Crop
7 18
7 18
7 18 7 18
7 18
7 18
7 18 7 18
7 18
7 18 7 18 7 18 7 18
Night temperature (°C)
21 15
12 20
28NS 23 34NS 32
11 8
8NS 9
9 10 7 9
22 39
19 14 21 14 24 18 25 16
Plant height (cm)
16NS 13
10 16
24NS 21 32NS 32
5 7
7NS 8
5.5 ,4.7 4.4 3.8
13 21
16 13 18 12 21 17 22 13
Length of main stem (cm)
14NS 14
10NS 10
22NS 23 38 31
17 25
14 15
7NS 7 5NS 5
14 20
18 24 18 21 21 25 21NS 21
No. of leaves
159NS 112
43NS 57
93NS 88 153NS 173
81 118
73NS 92
19 28 13NS 12
403 1332
39 77 41 57 65NS 74 162NS 157
Main stem leaf area (cm 2)
408 123
229 295
558NS 459 816 433
238NS 246
404 299
29 75 33 53
737 1745
534 451' 540 358 602NS 527 728 613
Total leaf area (cm 2)
8 4
12NS 12
25NS 24 38 30
6NS 6
16 11
6NS 4 6NS 5
9NS 8
23 19 23 20 : 19NS 20 20 15
No. of lateral shoots
3.5 1.0
1.8 1.5
5.9 2.2 8.7 2.4
1.6 1.2
2.5 1.1
0.4 0.3 0.3 0.3
9.0 11.0
5.8 2.3 7.3 2.3 7.0 3.7 4.8 2.9
Top dry weight (g)
14 May 13 March
17 April 3 April
28 April 3 April 19 May 4 April
12 April 28 March
19 April 19 April
8 March 21 February 27 February 20 February
22 May 27 April
9 May 15April 15 May 10 April 13 May 17 April 30 April 7 April
Date of anthesis
The influence of two night temperatures (15 h each night) on the growth characteristics of seedlings grown in greenhouses in 1989. Growth data expressed as means; n= 10 plants. All data pairs except those indicated NS are significantly different at the< 5% level due to temperature treatment as determined by F-test. Top dry weight was not analyzed statistically as each replicate crop of five plants was weighed together rather than individually
TABLE3
t~
,-q ,..] ~r
~7
©
© Z
300
R.H. MERRITT AND H.C. KOHL, JR.
crop was harvested on that date to have a morphological comparison when the first crop came into bloom. In 1989, growth data were taken when both crops were in bloom (Table 3) and as such was not a same-day comparison as in 1987. It was a bloom date comparison. Greenhouses were maintained from 08:00 to 17:00 h at 24-30°C. The warmer night greenhouse (WNT) was maintained at 18 +_3 °C from 17:00 to 18:00 h and the low night temperature (LNT) greenhouses at 7 +_3°C. The average mean daily temperature (daily m i n i m u m + m a x i m u m / 2 ) for (a) the WNT greenhouse was 21 °C for both 1987 and 1989 and (b) the LNT greenhouse was 15.5 ° C in 1987 and 13.5 ° C in 1989. The 2 ° C differential was due to lower daytime air temperatures in the LNT greenhouse in 1989 as compared to 1987. Air temperatures were measured to 0.1 °C with copper-constant thermocouples attached to a Campbell CR-7 datalogger and by recording hygrothermographs. Leaf areas were measured with a LI-COR 3100 area meter. Roots were not measured. Growth data were analyzed by an analysis of variance. Fuel energy calculations were performed using a computer program for the experimental greenhouses in which these studies were performed (Roberts, 1980; Simkins et al., 1984). The computer program is based on an average year of 5016 degree days. RESULTS AND DISCUSSION
P l a n t g r o w t h responses to night t e m p e r a t u r e (Tables 2 a n d 3) Dianthus. - Plants grown in the LNT greenhouse were 30-55% taller, had
more leaf area and top dry weight than those in the WNT. It took an additional 3-5 weeks for the LNT plants to bloom. In general, the four cultivars responded in a similar fashion to the two night temperatures and growth was better at the WNT. G e r a n i u m . - The growth response of plants of all cultivars in 1987 and 1989 was very similar. Those grown in the LNT were about one-half the height of the WNT plants, due to shorter main stems. The LNT plants remained short and very compact, even though they took 3 weeks longer to bloom, which has also been reported for 'Red Elite' and 'Cardinal Orbit' (Merritt and Kohl, 1989). I m p a t i e n s . - Plants grown in LNT were severely stunted, but eventually bloomed 54 days after the WNT plants. Marigold. - Plants of both cultivars 'Aurora' and 'Janie' grown in LNT were
shorter, had more lateral shoots, less leaf area, but similar dry weight when
RESPONSEOF BEDDING PLANTSTO LOW NIGHT TEMPERATURE
301
compared to W N T plants. L N T plants of'Aurora' took 10 and 15 days longer to bloom than W N T plants in 1987 and 1989, respectively. The lower daytime temperatures in 1989 caused the 5-day delay in bloom. Growth in 1987 was also substantially better than in 1989 due to the later transplanting date and warmer daytime temperatures. Cultivar 'Perfection' did not respond as well as the other two cultivars to L N T and required 3 weeks longer to bloom than W N T plants. - This crop grew better in L N T than WNT. The LNT plants bloomed on the same date as the W N T plants and were taller, had more lateral branches, more leaf area and more than twice as m u c h top dry weight.
Mimulus.
- Plants grown in L N T were taller, had fewer leaves and took 15 days longer to bloom than the W N T plants.
Pansy.
- Plants of both cultivars grown in L N T had more basal branches and were only about one-half the height of W N T plants, which is similar to the growth response of cultivar 'Snow Cloud' (Merritt and Kohl, 1989 ). Anthesis of L N T plants was delayed 9-12 days when compared to W N T plants. Petunia.
- Plants of both cultivars grew poorly in L N T and took 24-45 days longer to bloom. Snapdragon.
Plants grown in L N T were shorter, had less leaf area and took 24 days more to bloom when compared to plants grown at WNT. Verbena.
-
TABLE 4 Fuel costs associated with heating an 8.5 × 14.6 X 2.1-m greenhouse at 27 + 3 °C day air temperature ( 9 h) and either 7 + 3 ° C or 18 + 3 ° C night temperature ( 15 h ), January through April, in a standard New Jersey year with 5016 degree days. Fuel use in April is negligible at 7°C Month
Night temperature (°C)
Oil fuel (1)
January
7 18
February
Monthly difference (1)
( l m -2)
784 1991
1207
9.7
7 18
651 1745
1094
8.8
March
7 18
303 1506
1203
9.6
April
7 18
845
223
1.8
302
R.H. MERRITT AND H.C. KOHL, JR.
Plants grown at LNT took 68 days longer to bloom when compared with plants growth at WNT. Fuel savings in N e w Jersey to operate a greenhouse at 7 vs. 18 ° C nights for 15 h are highest in January, February and March (Table 4). Fuel savings at 7 ° C LNT decrease the longer it takes the crop to bloom in LNT vs. WNT. Growth characteristics in response to LNT and-fuel savings must be considered when devising greenhouse management plans to meet specific spring season markets for bedding plants. Each crop must be analyzed separately since crop response varies considerably among species and cultivars. These studies have shown the feasibility of producing some crops of bedding plants under low PPF and LNT conditions. Zinnia.
-
REFERENCES Merritt, R.H. and Kohl, H.C., Jr., 1983. Crop productivity efficiency of petunias in the greenhouse. J. Am. Soc. Hortic. Sci., 108: 544-548. Merritt, R.H. and Kohl, H.C., Jr., 1989. Crop production and morphology of petunia and geranium in response to low night temperature. J. Am. Soc. Hortic. Sci., 114: 44-48. Roberts, W.J., 1980. Computer program for determining fuel use in greenhouses in New Brunswick, NJ (unpublished). Shedlosky, M.E. and White, J.W., 1987. Growth of bedding plants in response to root zone heating and night temperature regimes. J. Am. Soc. Hortic. Sci., 112: 290-295. Simkins, J.C., Mears, D.R. and Roberts, W.J., 1984. Evaluation of an experimental greenhouse film with improved energy performance. Am. Soc. Agric. Eng. Pap. No. 84-4033, 28 pp.
295
Elsevier Science Publishers B.V., A m s t e r d a m
Morphology of bedding plants in response to low night temperature and energy use implications Richard H. Merritt and Harry C. Kohl, Jr.* Department of Horticulture, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, NJ 08903 (U.S.A.) (Accepted for publication 7 May 1990)
ABSTRACT Merritt, R.H. and Kohl, H.C., Jr., 1991. Morphology of bedding plants in response t o l o w night temperature and energy use implications. Scientia Hortic., 45: 295-302. Seedlings of bedding plant crops were grown in greenhouses, January-May 1987 and 1989, at day air temperatures of 27 + 3 ° C (9 h) and either 7 + 3 ° C or 18 + 3 ° C night air temperatures ( 15 h). Morphological evaluations of the crop response to night temperatures were taken and calculations of fuel energy required to operate greenhouses at 7 and 18 ° C were determined. Crops which grew well at 7°C and which were short, compact and bloomed quickly were mimulus (cultivar 'Yellow Flower'), marigold (cultivars "Aurora', 'Janie') and petunia (cultivars 'Crimson', 'Joy'). Other crops which grew well at 7°C, but took longer to bloom were geranium (cultivars 'Cardinal Orbit', 'Orbit Glow', 'Pink Elite', 'Violet Elite'), marigold (cultivar 'Perfection'), pansy (cultivar cultivar 'Universal Mix') and verbena (cultivar 'Springtime' ). Crops which were stunted or took too long to bloom were impatiens (cultivar 'Accent'), dianthus (cultivars 'Big Eye Crimson' and 'Scarlet', 'Magic Charm', 'Princess' ), snapdragon (cultivars 'Liberty', 'Pixie' ) and zinnia (cultivar 'Peter Pan' ). Fuel savings at 7 vs. 18°C were 9.7 1 of fuel oil per square meter in January, 8.8 in February, 9.6 in March and 1.8 in April. Keywords: Antirrhinum majus; bedding plants; Dianthus chinensis; fuel energy requirements; Impatiens holsti; Mimulus hybridus; Pelargonium × hortorum; Petunia hybrida; Tagetes patula; temperature; Verbena hortensis; Viola tricolor, Zinnia elegans. AbbreviatiOns: LAI = leaf area m - 2 surface; WNT = warm night temperature; LNT = low night temperature; PPF = photosynthetic photon flux.
INTRODUCTION
Greenhouse production of bedding plants for spring sales in northern latitudes may be adversely affected by low light intensities (photosynthetic photon flux, PPF) and high fuel costs to heat greenhouses in January through April. Cultivar "Snow Cloud' petunias grown in greenhouses (Merritt and *Present address: California Agricultural E x p e r i m e n t a l Station, Davis, CA 95616, U.S.A.
0304-4238/91/$03.50
© 1991 - - Elsevier Science Publishers B.V.
296
R.H. MERRITT AND H.C. KOHL, JR.
Kohl, 1989 ) held at day temperatures of 21 and 27 ° C, respectively, and 7 ° C night temperatures had more basal branches and were one-third the height of those grown at a 27 ° C day and 18 ° C night temperature. Anthesis was delayed 10 days at the 7 °C night temperature. Cultivars 'Red Elite' and 'Cardinal Orbit' geraniums grown at 27 ° C day and either 7 or 18 ° C night temperature had a growth response similar to petunia, but the 7 ° C crop was much shorter and more compact than those grown at 18 ° C and anthesis was delayed 3 weeks. These studies also supported the hypothesis that at low PPF, geranium and petunia can produce dry matter per square meter with equal efficiency under both normal and low night temperatures when the plant canopy is closed to trap the available light, and when the plants are not sink limited, i.e. have many lateral branches (Merritt and Kohl, 1983; Shedlosky and White, 1987 ). The studies reported here were designed to determine whether or not other commercially important bedding plant crops can successfully be grown at low night temperatures and low PPF. Plant characteristics, dry matter production and fuel costs to produce crops to anthesis were considered. MATERIALSAND METHODS Crops selected for evaluation in 1987 and 1989 are listed in Table 1. Seeds of all crops (Goldsmith Seeds, Gilroy, CA) were sown on 8 January 1987 and 4 January 1989, except geranium on 16 January, in New Brunswick, NJ. Seedlings were grown at a m i n i m u m 21 ° C day/18 ° C night air temperatures on porous concrete benches that maintained the medium at 24-26 ° C. In 1987, geranium seedlings were transplanted on 29 January into 13-cm square plastic pots, impatiens were transplanted on 23 January, and petunias and marigolds on 28 January, all into 10-cm square plastic pots. In 1989, seedling transplanting for marigolds was on 17 January, dianthus on 20 January, mimulus, pansy, snapdragon, verbena and zinnia on 25 January, and geranium on 6 February. Mimulus, pansy, zinnia and geranium were transplanted into 10-cm square plastic pots; dianthus, marigold, snapdragon and verbena into 5-cm square plastic pots. In both years, plants from each bedding plant cultivar were visually matched into groups to achieve visually identical treatment blocks (Merritt and Kohl, 1989 ). Differential temperature treatments began within 1 week after transplanting. In 1987, pot-to-pot spacing was maintained throughout the experiments and there was one replicate of four plants for each crop in each greenhouse. In 1989, pot-to-pot spacing was maintained until plant canopy closure, at which time the pots were respaced as described in Table 1. Two replicates of five plants each for each crop were placed in both the 7 and 18 ° C greenhouses. To minimize edge effects, pots with seedlings of comparable size were used to form two border rows on all sides of each treatment. In 1987, growth data were taken when the 18°C crop was 50% in bloom (Table 2). The 7°C
RESPONSE OF BEDDING PLANTS TO LOW NIGHT TEMPERATURE
297
TABLE1 The influence of two night temperatures ( 15 h each night) on anthesis of bedding plants grown in the greenhouse, January through May, 1987 and 1989. The n u m b e r of days is from the first true leaf stage of growth to anthesis. Anthesis in 1987 was the date when the 18 °C crop had one-half the plants in flower. It is a same-day comparison between the 18 and 7°C crops. In 1989, anthesis was when both the 18 and 7 ° C crops were 50% in flower. Leaf area index ( LAI ) = leaf area m - 2 surface Year/crop
Cultivar
Night temperature ( ° C)
1987 Geranium
('Orbit Glow')
7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18
88 68 88 67 88 68 89 35 31 21 60 39 51 43 55 43
59 59 59 59 59 59 100 100 100 100 100 100 100 100 100 100
4.0 8.3 4.1 7.7 3.5 7.4 0.4 5.2 2.1 5.4 3.6 5.8 7.5 8.6 7.1 7.3
7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18 7 18
92 68 98 63 96 70 83 60 99 74 42 27 33 26 68 68 61 46 102 57 80 56 70 56 109 41
162 167 159 175 149 152 146 146 57 52 217 241 275 250 97 97 97 84 149 148 158 148 167 166 97 66
6.6 5.4 6.7 4.4 7.4 6.1 9.0 7.6 3.2 7.6 0.4 0.9 0.4 0.7 3.9 2.9 1.0 1.1 10.1 5.3 6.9 5.7 2.8 3.6 1.8 0.5
('Pink elite' ) ('Violet elite') Impatiens
('Accent')
Marigold
('Aurora') ('Perfection')
Petunia
('Crimson') ('Joy')
1989 Dianthus
('Big Eye Crimson') ('Big Eye Scarlet') ('Magic Charm' ) ('Princess')
Geranium
('Cardinal Orbit')
Marigold
('Aurora') ('Janie')
Mimulus
('Yellow Flower')
Pansy
('Universal Mix')
Snapdragon
( 'Liberty' ) ('Pixie')
Verbena
('Springtime')
Zinnia
('Peter Pan' )
No. of days from start of experiment to anthesis
Final spacing of pots m -2
LAI at anthesis
('Joy')
Petunia ('Crimson')
('Perfection')
Marigold ('Aurora')
7 t8
7 18
7 18
7 18
14 31
14 27
18 22
12 15
5 22
7
15 34
15 31
16 39
Plant height (cm)
18
7 18
('Violet elite')
Impatiens ('Accent')
7 18
7 18
Night temperature (°C)
('Pink elite')
Geranium ('Orbit Glow')
Crop
9 24
10 19
14 17
8 11
18
3
6 11
6 13
6 13
Length of main stem (cm)
20NS 20
17NS 18
16NS 17
11NS 14
-
-
13 17
12NS 14
13NS 14
No. of main stem leaves
320 233
320 168
-
-
-
322 762
376 528
519 854
Main stem leaf area (cm 2)
1090 727
745NS 858
362 581
214 547
38 516
591 1253
698 1297
678 1409
Total leaf area (cm 2)
14 11
11 9
-
-
8 11
llNS 11
11NS 11
10NS 8
No. of lateral shoots
2.9NS 3.1
3.5NS 3.0
2.2NS 2.8
1.4 2.6
0.2 2.0
4.1 7.3
4.9 7.3
4.6 7.8
Top dry weight (g)
6 April 25 March
3 April 25 March
6 April 17 March
9 March 26 February
1 May 12 March
4May 14 April
4 May 13 April
4 May 14 April
Date of anthesis
Theinfluence of two night temperatures (15 h each night) on the growth characteristics of seedlings grown in greenhouses in 1987. Growth data expressed as means; n = 4 plants. All data pairs except those indicated NS are significantly different at ~he < 5% level due to temperature treatment as determined by F-test
TABLE 2
~7
tO
Zinnia ('Peter Pan' )
Verbena ('Springtime')
('Liberty')
Snapdragon ( 'Pixie' )
Pansy ('Universal Mix' )
Mimulus ( 'Yellow Flower' )
('Janie')
Marigold ('Aurora')
Geranium ('Cardinal Orbit' )
('Princess')
('Magic Charm' )
('Big Eye Scarlet' )
Dianthus ('Big Eye Crimson')
Crop
7 18
7 18
7 18 7 18
7 18
7 18
7 18 7 18
7 18
7 18 7 18 7 18 7 18
Night temperature (°C)
21 15
12 20
28NS 23 34NS 32
11 8
8NS 9
9 10 7 9
22 39
19 14 21 14 24 18 25 16
Plant height (cm)
16NS 13
10 16
24NS 21 32NS 32
5 7
7NS 8
5.5 ,4.7 4.4 3.8
13 21
16 13 18 12 21 17 22 13
Length of main stem (cm)
14NS 14
10NS 10
22NS 23 38 31
17 25
14 15
7NS 7 5NS 5
14 20
18 24 18 21 21 25 21NS 21
No. of leaves
159NS 112
43NS 57
93NS 88 153NS 173
81 118
73NS 92
19 28 13NS 12
403 1332
39 77 41 57 65NS 74 162NS 157
Main stem leaf area (cm 2)
408 123
229 295
558NS 459 816 433
238NS 246
404 299
29 75 33 53
737 1745
534 451' 540 358 602NS 527 728 613
Total leaf area (cm 2)
8 4
12NS 12
25NS 24 38 30
6NS 6
16 11
6NS 4 6NS 5
9NS 8
23 19 23 20 : 19NS 20 20 15
No. of lateral shoots
3.5 1.0
1.8 1.5
5.9 2.2 8.7 2.4
1.6 1.2
2.5 1.1
0.4 0.3 0.3 0.3
9.0 11.0
5.8 2.3 7.3 2.3 7.0 3.7 4.8 2.9
Top dry weight (g)
14 May 13 March
17 April 3 April
28 April 3 April 19 May 4 April
12 April 28 March
19 April 19 April
8 March 21 February 27 February 20 February
22 May 27 April
9 May 15April 15 May 10 April 13 May 17 April 30 April 7 April
Date of anthesis
The influence of two night temperatures (15 h each night) on the growth characteristics of seedlings grown in greenhouses in 1989. Growth data expressed as means; n= 10 plants. All data pairs except those indicated NS are significantly different at the< 5% level due to temperature treatment as determined by F-test. Top dry weight was not analyzed statistically as each replicate crop of five plants was weighed together rather than individually
TABLE3
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300
R.H. MERRITT AND H.C. KOHL, JR.
crop was harvested on that date to have a morphological comparison when the first crop came into bloom. In 1989, growth data were taken when both crops were in bloom (Table 3) and as such was not a same-day comparison as in 1987. It was a bloom date comparison. Greenhouses were maintained from 08:00 to 17:00 h at 24-30°C. The warmer night greenhouse (WNT) was maintained at 18 +_3 °C from 17:00 to 18:00 h and the low night temperature (LNT) greenhouses at 7 +_3°C. The average mean daily temperature (daily m i n i m u m + m a x i m u m / 2 ) for (a) the WNT greenhouse was 21 °C for both 1987 and 1989 and (b) the LNT greenhouse was 15.5 ° C in 1987 and 13.5 ° C in 1989. The 2 ° C differential was due to lower daytime air temperatures in the LNT greenhouse in 1989 as compared to 1987. Air temperatures were measured to 0.1 °C with copper-constant thermocouples attached to a Campbell CR-7 datalogger and by recording hygrothermographs. Leaf areas were measured with a LI-COR 3100 area meter. Roots were not measured. Growth data were analyzed by an analysis of variance. Fuel energy calculations were performed using a computer program for the experimental greenhouses in which these studies were performed (Roberts, 1980; Simkins et al., 1984). The computer program is based on an average year of 5016 degree days. RESULTS AND DISCUSSION
P l a n t g r o w t h responses to night t e m p e r a t u r e (Tables 2 a n d 3) Dianthus. - Plants grown in the LNT greenhouse were 30-55% taller, had
more leaf area and top dry weight than those in the WNT. It took an additional 3-5 weeks for the LNT plants to bloom. In general, the four cultivars responded in a similar fashion to the two night temperatures and growth was better at the WNT. G e r a n i u m . - The growth response of plants of all cultivars in 1987 and 1989 was very similar. Those grown in the LNT were about one-half the height of the WNT plants, due to shorter main stems. The LNT plants remained short and very compact, even though they took 3 weeks longer to bloom, which has also been reported for 'Red Elite' and 'Cardinal Orbit' (Merritt and Kohl, 1989). I m p a t i e n s . - Plants grown in LNT were severely stunted, but eventually bloomed 54 days after the WNT plants. Marigold. - Plants of both cultivars 'Aurora' and 'Janie' grown in LNT were
shorter, had more lateral shoots, less leaf area, but similar dry weight when
RESPONSEOF BEDDING PLANTSTO LOW NIGHT TEMPERATURE
301
compared to W N T plants. L N T plants of'Aurora' took 10 and 15 days longer to bloom than W N T plants in 1987 and 1989, respectively. The lower daytime temperatures in 1989 caused the 5-day delay in bloom. Growth in 1987 was also substantially better than in 1989 due to the later transplanting date and warmer daytime temperatures. Cultivar 'Perfection' did not respond as well as the other two cultivars to L N T and required 3 weeks longer to bloom than W N T plants. - This crop grew better in L N T than WNT. The LNT plants bloomed on the same date as the W N T plants and were taller, had more lateral branches, more leaf area and more than twice as m u c h top dry weight.
Mimulus.
- Plants grown in L N T were taller, had fewer leaves and took 15 days longer to bloom than the W N T plants.
Pansy.
- Plants of both cultivars grown in L N T had more basal branches and were only about one-half the height of W N T plants, which is similar to the growth response of cultivar 'Snow Cloud' (Merritt and Kohl, 1989 ). Anthesis of L N T plants was delayed 9-12 days when compared to W N T plants. Petunia.
- Plants of both cultivars grew poorly in L N T and took 24-45 days longer to bloom. Snapdragon.
Plants grown in L N T were shorter, had less leaf area and took 24 days more to bloom when compared to plants grown at WNT. Verbena.
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TABLE 4 Fuel costs associated with heating an 8.5 × 14.6 X 2.1-m greenhouse at 27 + 3 °C day air temperature ( 9 h) and either 7 + 3 ° C or 18 + 3 ° C night temperature ( 15 h ), January through April, in a standard New Jersey year with 5016 degree days. Fuel use in April is negligible at 7°C Month
Night temperature (°C)
Oil fuel (1)
January
7 18
February
Monthly difference (1)
( l m -2)
784 1991
1207
9.7
7 18
651 1745
1094
8.8
March
7 18
303 1506
1203
9.6
April
7 18
845
223
1.8
302
R.H. MERRITT AND H.C. KOHL, JR.
Plants grown at LNT took 68 days longer to bloom when compared with plants growth at WNT. Fuel savings in N e w Jersey to operate a greenhouse at 7 vs. 18 ° C nights for 15 h are highest in January, February and March (Table 4). Fuel savings at 7 ° C LNT decrease the longer it takes the crop to bloom in LNT vs. WNT. Growth characteristics in response to LNT and-fuel savings must be considered when devising greenhouse management plans to meet specific spring season markets for bedding plants. Each crop must be analyzed separately since crop response varies considerably among species and cultivars. These studies have shown the feasibility of producing some crops of bedding plants under low PPF and LNT conditions. Zinnia.
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REFERENCES Merritt, R.H. and Kohl, H.C., Jr., 1983. Crop productivity efficiency of petunias in the greenhouse. J. Am. Soc. Hortic. Sci., 108: 544-548. Merritt, R.H. and Kohl, H.C., Jr., 1989. Crop production and morphology of petunia and geranium in response to low night temperature. J. Am. Soc. Hortic. Sci., 114: 44-48. Roberts, W.J., 1980. Computer program for determining fuel use in greenhouses in New Brunswick, NJ (unpublished). Shedlosky, M.E. and White, J.W., 1987. Growth of bedding plants in response to root zone heating and night temperature regimes. J. Am. Soc. Hortic. Sci., 112: 290-295. Simkins, J.C., Mears, D.R. and Roberts, W.J., 1984. Evaluation of an experimental greenhouse film with improved energy performance. Am. Soc. Agric. Eng. Pap. No. 84-4033, 28 pp.