Greenhouse Management and Crops

Section 4

Unit 13, 14, 15

Poinsettias

Unit 13

History

• Poinsettias were grown in Southern California as cut flowers in 1900

• Today, growing poinsettias is a big part of many horticultural operations

Greenhouse management

• Factors to consider in greenhouse production are…– Temperature– Moisture– Ventilation– Climate

Temperature

• Important to growing a successful crop

• Day temp. should be 5-10 degrees higher than night temp.

• Thermometers should be at the plant level, out of direct sunlight to ensure optimum growth

Moisture

• Plant growth is dependent on moisture

• Influences relative humidity

• Amount of water needed depends on the type of plant and the outside conditions on a particular day

• Appearance and feel of the medium is an indication for watering plants

Ventilations

• Movement and exchange of air in the greenhouse

• Should be able to feel the air movement in the greenhouse

• Ensures correct temp and relative humidity

• Helps control plant diseases

Climate

• Directly influences the type of greenhouse structure, heating and cooling systems

Poinsettia Flower

• Small, yellow flower that grows at the terminal end of the plant

• Just below the flower are the bracts– Leaves that give the poinsettias their color– Most common color is red

• Require a short day for the production of the flower• Should be grown in full sunlight• During months w/ long days, the plants develop

leaves and increase stem length

Growing Poinsettias

• Start from a 2 ¼” rooted poinsettia cutting– Be sure the plant is healthy

• Plant in pots 4”, 5”, 6” 7” 8” or 10”

• Night temp should be 65 degrees

• Day temp should be 70 – 75 degrees

Pinching

• Process of removing the terminal end of the plant• Accomplished by taking the top of the plant

between the thumb and index finger and carefully breaking the top of the poinsettia completely off

• 4-5 leaves should remain on the plant• After pinching, new shoots called breaks will

develop from the bud in the axis of the node– Each shoot will produce a flower

• Main reason for pinching is to increase the number of bracts per plant

Soil Mixes

• May be grown in many different media• Must be porous and well-drained• Should be free of insects and disease

organisms• Should have good nutrient-holding

capabilities• Soil can be sterilized at 180 degrees for 30

minutes

Fertility

• Fertilizer should be complete– Contain nitrogen, phosphorus, and potassium

• Follow manufacturer’s recommendations for application

Growth regulators

• Growth regulators have 2 main purposes– Control the height of the plant– Improve quality of color in bracts

• Applied as a soil drench or foliar spray• Examples:

– Cycocel– Ancymidol– Bonzi– B-nine

• Height can be controlled to some extent by adjusting light level and durations and by regulating day and night temps– Brighter light results in more compact plants– Shorten plants by lower daytime than nighttime

temp

Maintaining Poinsettias

• Handle new plants carefully

• Protect from insects using chemical pesticides

• Protect from attack by disease organisms– Clean poinsettias must be purchased– Clean growing media must be used– Treat w/ fungicide when transplanted

Chrysanthemums

Unit 14

Chrysanthemums

• The most popular cut flower sold in the US

• Because of artificial control of day and night in the greenhouse, they can be grown throughout the entire year

• Most popular on Mother’s Day, Easter, and Memorial Day

Determining market and variety

• Schedule planting so that plants bloom at desired time

• Some varieties bloom in 8 weeks after the start of short days, others 10, 12, or 14 weeks

• This is known as response time– Chrysanthemums are cataloged by their

response time

Regulating Light

• Mums are a short-season crop– Sets flower buds and blooms only when nights

are long and days are short

• Control light when…– Rooted cuttings are 1st potted – days kept long

and nights short (7 hrs of darkness max)– Summer flowering is desired, days kept short

and nights long to encourage proper timing of flower bud formation

Obtaining Starter Plants

• Propagated by softwood cuttings

• Diseases may be passed along from parent plants

• Very important to purchase rooted cuttings from disease free retailers

Establishing a growing schedule

• A growing schedule must be established before ordering rooted cuttings

• Start at the end of the schedule (the blooming date)

• Control day and night lengths to follow the schedule

Planted rooted cuttings

• 6-inch plastic pot is a good choice for planting rooted mum cuttings– Requires 5 cuttings per pot

• Well drained medium that holds moisture well• Water added to the medium should quickly drain

to the bottom of the pot• Don’t let the potted cuttings dry out

– Provide a constantly moist, but not wet soil– Add water when the top of the potting medium 1st

appears to be drying out

Caring for Potted Cuttings

• Greenhouse temp should be @ 63 degrees at night when 1st placed in the growing area

• Higher temps promote faster vegetative growth• If temp drops below 60 degrees flower buds may

not set evenly• Temps are dropped to 62 degrees and then to 55

degrees for the last 3 weeks– Cooler temp tends to harden off the plants

Fertilizing cuttings

• Constant application of fertilizer– Diluted fertilizer may be added to the irrigation water

• Slow release fertilization– Mixed in the potting medium at the time of planting

• Timed applications– Apply once every 2-3 weeks in irrigation or to the pot

as needed

Watering

• Frequency varies w/ temperature and humidity and water holding capacity of the medium

• Hot & Dry weather, twice a day• Other times, once a day or every other day• Check soil frequently and add water whenever top

of medium is beginning to appear dry• Do not keep soil saturated

Pinching and Disbudding

• Pinch off ¼ to ½” of stem growth– Causes shoots to develop resulting in more

branches

• Ideal mum should have about 10-15 flowers per pot

Growth Retardants

• Similar to Poinsettias

• Controlling insects and disease

• Good sanitation and cultural practices often all the control needed