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