Photoperiodic Greenhouse Crops

1. Photoperiodic Greenhouse Crops Competencies 14.00-16.00

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 20-20-20 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 70-75 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