1. Temperature Control of Growth & Flowering in Ornamentals
Krishna Nemali, Ph.D.
Purdue University
(765)

2. Why is temperature important?
Temperature affects growth (along with light) and differentiation (solely) in plants
Growth
Differentiation

3. Average temperature in Kentucky (C)
Bomford et al., 2007
F M A M J J A S O N D J

4. What is the optimum temperature for flowering plants?
F M A M J J A S O N D J
-10 C
0 C
10 C
20 C
30 C
40 C
50 C
68 F
Optimum
78 F
Average temperature (C)

5. Optimum temperature for several flowering plants

6. Crop growth slows down at suboptimal temperatures
F M A M J J A S O N D J
-10 C
0 C
10 C
20 C
30 C
40 C
50 C
68 F
Optimum
78 F
Average temperature (C)
50 F
Slow growth
Tip:
Crops like alyssum, pansy and chrysanthemum can tolerate 50 F temperatures

7. Effect of temperature on growth of salvia plugs
Courtesy: Lee Ann Pramuk and Erik Runkle

8. Low temperature controls plant growth but it comes with the cost of delayed flowering
Courtesy: Lee Ann Pramuk and Erik Runkle

9. Low temperature controls plant growth but it comes with the cost of delayed flowering
Courtesy: Lee Ann Pramuk and Erik Runkle

10. Hanging baskets ~$3.00 more revenue per basket High tunnel
Heated greenhouse
Courtesy: Greenhouse Grower

11. Heating is more important for cold sensitive than cold tolerant crops
Delay per degree F decrease in temp
Orchids
~ 7 days
Petunia
~ 3 days
Impatiens
~ 2 days
Pansy
~ 1.5 days

12. Mean daily temperature (MDT)
Case 1:
70 F day (12 h) /48 F night (12 h)
MDT = ( )/2 = 59 F
Case 2:
65 F day (12 h) /53 F night (12 h)
MDT = (65 +53)/2 = 59 F
Case 3:
70 F day (14 h) / 44 F night (10 h)
MDT = [(70 x 14) + (44 x10)]/ 24 = 1416/24 = 59 F

13. Flowering is affected by “mean daily temperature”
Tip:
Maintain higher temperature for a few hours in the greenhouse during warmest part of the day to increase MDT and flowering
Erwin and Heins, 1994

14. A note about wood burning stoves used for greenhouse heating
Higher CO2 concentration in a high tunnel can reduce uptake of certain nutrients like calcium which may further lower cut flower quality in storage

15. At temperatures slightly higher than optimal, stretching is observed
83 F
30 C
Stretching
78 F
Optimum
20 C
68 F
Average temperature (C)
10 C
0 C
-10 C
F M A M J J A S O N D J

16. Stretching is not generally affected by ‘absolute’ day temperature
Erwin and Heins, 1994

17. Stretching is affected by the ‘difference’ between day & night temperatures
Erwin and Heins, 1994

18. Negative DIF can be used to control stretching
DIF = day temperature – night temperature
Negative DIF means warmer night and cooler day
Day/Night temp
Erwin and Heins, 1994
(mean temp)

19. Negative DIF can be used to control stretching
Provide negative DIF 5-7 F difference
Usually 2-3 hours of –DIF at sun rise is sufficient
Provide –DIF when plants are growing fast
Effects start within 48 hr.
Watch for leaf yellowing
French marigold, aster, tulips, hyacinths are not responsive to -DIF

20. Both crop growth and flowering are affected at supra high temperatures
Slow growth and decreased flowering
83 F
30 C
Stretching
78 F
Optimum
20 C
68 F
Average temperature (C)
10 C
Tip:
Crops like marigold, vinca, petunia, rudbeckia and zinnia can tolerate 90 F temperatures
0 C
-10 C
F M A M J J A S O N D J

21. Temperature inside the high tunnel during a day in June at Ithaca, NY
95 F
77 F
H.S. Wein, 2009

22. Effect of short duration exposure to high temperature on growth and flowering in salvia
Courtesy: LSU Ag Center

23. Which method is right? Why?
Shade cloth
Shade cloth
High tunnel
High tunnel A B