Photoperiodic Greenhouse Crops Competencies 14.00-16.00

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

Chrysanthemums

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

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

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

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

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

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

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

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

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.

Poinsettias

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

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

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

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

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.

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