1. Photoperiodic Greenhouse Crops
Competencies

2. Photoperiodism
The response of different periods of day and night in terms of plant growth and maturity
Long day plants flower when days are long and nights are short
Short day plants flower when days are short and nights are long
Chrysanthemums
Poinsettias

3. Chrysanthemums

4. Chrysanthemums Most popular cut flower sold in the U.S.
Popular as a potted plant for Mother’s Day, Memorial Day, and Easter
Second only to poinsettias in dollar value for potted flowers
Many different cultivars are grown

5. Planting Chrysanthemums
Rooted cuttings are available from wholesale growers
The number of plants to use depends on the pot size
4” pot has 2 plants
5” pot has 4 plants
6” pot has 5 plants

6. Chrysanthemum Temperatures
During the first two weeks
Greenhouse temperature should be 63 degrees F at night and on cloudy days
On sunny days the temperature should be 70 degrees F

7. Chrysanthemum Temperatures
After the first two weeks
Greenhouse temperature should be kept at 62 degrees F at night and on cloudy days
On sunny days temperature should be kept at 70 degrees F

8. Chrysanthemum Temperatures
During the last three weeks
Greenhouse temperatures should be kept at 55 degrees at night and on cloudy days
On sunny days greenhouse temperatures should be kept at 65 degrees
Uneven bud set is caused by improper temperatures

9. Pinching Chrysanthemums
Pinching is done to make a more compact plant with more flowers
Disbudding is done to control or reduce the number of flowers per plant

10. Media and Fertilization
Media must be free of diseases and insects
Soil must be porous and well drained
Regular fertilization should be done with a liquid fertilizer at 250 ppm at each watering

11. Chrysanthemum Photoperiod
Short-day plant
Bud set light period is 14 ½ hours or less of light, and flower development takes place when daylight is 13 ½ hours or less
Vegetative growth takes place when light period is less than 12 ½ hours

12. Chrysanthemum Photoperiod
From August to May 15, light is used during the middle of the night to break the long dark periods
From March 15-October 20, black cloth is used to give about 12 hours of darkness from about 5 p.m. to 7 a.m.

13. Poinsettias

14. Poinsettias Most important pot plant grown for the Christmas season
Many different cultivars are grown

15. Planting Poinsettias Wholesale growers supply 2 ¼” rooted cuttings
Number of plants per pot depends on pot size, whether plants will be pinched or grown as a single stem, and size of flower
4” pot has 1 plant for pinched or for single stem
6” pot has 2 plants for pinched or 3-4 for single stem
8” pot has 3-4 plants for pinched and 6-7 for single stem

16. Poinsettia Temperatures
Greenhouse temperatures should be 65 degrees F at night and degrees F during the day
Some cultivars vary slightly
If night temperatures get above 80 degrees F, flowering will be delayed or may not flower at all

17. Pinching Poinsettias
Pinching may be done to increase the number of bracts on the plant and to make the plants appear fuller.

18. Media and Fertilization
Media must be free from insects and diseases.
Soil must be porous and well-drained
Large amounts of fertilizer are needed from propagation until sold.

19. Poinsettia Photoperiod
Short-day plant
Bud set light period is from 12 hours to 12 hours, 15 minutes
Vegetative growth light period is longer than 12 hours
Two hours of light from about 11 p.m. to 1 a.m. each night will cause short day effect