Basics of Forced Flowering Perennials

Royal D. HeinsOro Farms

What information do you need to produce flowering perennials?

• Green or in flower• Space availability and when• Acceptable input costs• Pot size• Facility availability

Equipment needed to produce perennials

• Heated greenhouse• Long-day lighting• Photosynthetic lighting• Short-day environment• Cooler

• Late source of plants

Grower issueSell green XSell in Flower Accelerate Delay

Heated greenhouseLong day lightingPhotosynthetic lightingShort Day environmentCoolerLate source of plants

Situation

Grower issueSell green XSell in Flower X Accelerate Delay

Heated greenhouseLong day lightingPhotosynthetic lightingShort Day environmentCoolerLate source of plants

Situation

Grower issueSell green XSell in Flower X Accelerate X Delay

Heated greenhouseLong day lightingPhotosynthetic lightingShort Day environmentCoolerLate source of plants

Situation

Grower issueSell green XSell in Flower X Accelerate X Delay X

Heated greenhouseLong day lightingPhotosynthetic lightingShort Day environmentCoolerLate source of plants

Situation

Grower issueSell green XSell in Flower X Accelerate X X Delay X X

Heated greenhouseLong day lightingPhotosynthetic lightingShort Day environmentCoolerLate source of plants

Situation

Let’s talk about perennials, then come back and identify the best

plants for the situations and what is needed to force out of

natural season.

1st Year Subsequent Years

Emergence

Dormancy Flowering

Vernalization

Winter

Fall Summer

Long Days

Spring

Winter

Spring / SummerSeed

Germination

Dormancy Juvenile Growth

Maturity

Vernalization

FallShort DaysCooler temps.

Herbaceous perennial life cycle

Flowering Mechanisms

Juvenile plant

Mature plant

FlowerWarm temps.

Flower

Cold required

Warm temps.

Cold required

requiredLong days

FlowerWarm temps.

requiredLong days

FlowerWarm temps.

Horticultural Perennial Flowering Schedules

Summer Fall Winter Spring Summer

Summer Fall Winter Spring Summer

PlantPlant Grow to FlowerGrow to Flower

Vernalize Grow to FlowerPlant Bulk

Plant Bulk

In the field

Plant Material from Plugs

Plant to finish pot

Force to Flower

Bulking

Vernalization

Seed

Vernalization

Bulking

Germination

Force to Flower

Plant

Juvenility

Vegetative Cutting

Vernalization

Bulking

Rooting

Force to Flower

Plant

Plant Material from Bareroot Clumps

PropaguleSeed Rooted Cuttingor

Division

Bulk during summer

Force to flower

Plant to field

Dig from field

Vernalize in cooler

Plant during winter or early spring

Plant to finish pot

Bulk

Vernalize

Force to flower

Keys to Success

• Mature plants• Proper plant size• Proper cold treatment• Proper photoperiod• Proper timing• Adequate light

Keys to Success

• Mature plants – plants not juvenile

Juvenility

– Usually refers to seed-propagated plants

– This is a period where plants will not flower even if given appropriate environments

– A plant must reach maturity to flower

Not by the size of the plug tray in which it was produced…

How Can You Tell if an Herbaceous Perennial is Mature?

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How Can You Tell if an Herbaceous Perennial is Mature?

Plant leaf number is the key.

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• Plug size by itself does not provide the answer.• But, older plants in larger plug trays have a higher potential to be mature.

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Age Requirements for Flowering Common Herbaceous Perennials

Aquilegia Columbine Some species require at least 15 leaves to flower consistently

Aster alpinus Alpine aster Plants require at least 15 leaves to flower consistently

Astilbe arendsii Astilbe Plants with five to six leaves flowered very inconsistently

Coreopsis ‘Sunray’ Tickseed Juvenile phase ends with about 16 leaves

Echinacea purpurea Coneflower Plants with four leaves flower

Euphorbia epithymoides Cushion spurge Plants with six to eight leaves failed to flower

Goniolimon tatarica Statice Plants with 10 to 14 leaves failed to flower

Heuchera sanguinea Coral bells Plants require 16 leaves to flower consistently

Physostegia virginiana Obedient plant Plants require at least 10 leaves to flower consistently

Veronica spicata ‘Blue’ Speedwell Plants with six to eight leaves will flower

Plant name Common name Age requirements

Lack of flowering may be caused by juvenility or lack of adequate vernalization

Keys to Success

• Mature plants• Proper plant size

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Considerations• Container size for finished product• Planting date (time to bulk before flower

induction)

Horticultural Perennial Flowering Schedules

Summer Fall Winter Spring Summer

Summer Fall Winter Spring Summer

PlantPlant Grow to FlowerGrow to Flower

Vernalize Grow to FlowerPlant Bulk

Plant Bulk

In the field

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Available Plant Sizes

• Plug trays– 512-cell– 288-cell– 128-cell– 72-cell– 50-cell– 36-cell

• 2-1/4 inch pots• Field grown, bare-root divisions or clumps

Previous year

Current year

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Starting Material Influences• Flowering percentage (if plant has a juvenile

phase)

• Plant size at flowering

• Flower number

• Time to flower

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Starting Plant Sizes

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Influence of Starting Size on Subsequent Flowering of Plants

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Starting Material• Disease free

Artemisia ‘Silver Mound’

Echinacea

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Starting Material• Disease free• Uniform development

Phlox paniculata

Aquilegia

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Starting Material• Disease free• Uniform development• Multiple eyes (buds)

Multiple buds produce a full pot

More lateral buds will yield more shoots to fill the pot

More lateral buds will yield more shoots to fill the pot

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Points to Remember• Determine final container size

• Select starting material that is an appropriate size based on the planting date

• The larger the starting plant material and the earlier the plant is potted, the larger the finish plant

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Points to Remember• To produce large plants

– Bulk small plants before flower induction– Plant multiple small plugs into one large pot– Start with large plant material with multiple

shoots

Keys to Success• Mature plants• Proper plant size• Proper cold treatment

Flowering Mechanisms

Juvenile plant

Mature plant

FlowerWarm temps.

Flower

Cold required

Warm temps.

Cold required

requiredLong days

FlowerWarm temps.

requiredLong days

FlowerWarm temps.

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Responses to Cold Treatment

• Cold treatment not recommended

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Cold Treatment Not Recommended

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Cold Treatment Not Recommended

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Responses to Cold Treatment

• Cold treatment not recommended• No response to cold treatment

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No Response to Cold Treatment

No cold 15-weeks cold

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Responses to Cold Treatment• Cold treatment not recommended• No response to cold treatment• Cold treatment beneficial

– Increased flowering percentage– Decreased time to flower– Increased flower number– Improve flower uniformity

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Cold Treatment Beneficial

No cold 15-weeks cold

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Responses to Cold Treatment• Cold treatment not recommended• No response to cold treatment• Cold treatment beneficial• Cold treatment required

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Delivering Cold Treatment• Cool seedlings or cuttings in the plug tray

– Plants that are mature, not juvenile

• Pot in larger container, grow until mature and then place in a cooler or cold greenhouse– Species with a juvenile phase – Plants that do not have the minimum recommended

number of leaves

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Delivering Cold Treatment• In a cooler

– Nine-hour photoperiod

– Lights delivering about 50 footcandles

• In a greenhouse

• Under a thermal blanket outdoors

• Purchase plugs that have been cooled

Overwintering and cooling outside

Overwintering view of 2-gallon pots

Production greenhouse overwintering perennials

Hosta overwintered

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Delivering Cold Treatment

Forcing Perennials for Sale in Flower_________________________________________________________

Salvia liners in cooler

Perennial plugs cooling and holding in cooler

Perennial plugs in cooler

Plant appearance after cooling can be “ugly”

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Effective Temperatures• Range from 32°F (0°C) to 45°F (7°C)

• 41°F (5°C) is recommended

• Temperatures below freezing can be used but,

• Avoid temperatures below 28°F (-2°C)

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Duration• Varies by species

• Most species will flower properly following 6-weeks cold, but some may require up to 10 weeks of cold.

Keys to Success

• Mature plants• Proper plant size• Proper cold treatment• Proper photoperiod

1st Year Subsequent Years

Emergence

Dormancy Flowering

Vernalization

Winter

Fall Summer

Long Days

Spring

Winter

Spring / SummerSeed

Germination

Dormancy Juvenile Growth

Maturity

Vernalization

FallShort DaysCooler temps.

Herbaceous perennial life cycle

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Changes in Natural PhotoperiodVariations in day length for different latitudes in the Northern Hemisphere

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Types of Photoperiod Responses

• Day-neutral plants (DNP)

• Short-day plants (SDP)

• Long-day plants (LDP)

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Perennials in Northern Climates

• DNP = no response to long days (generally

only after cold)

• Facultative LDP = long days beneficial

• Obligate LDP = long days required

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Day-Neutral Plant

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Facultative Long-Day Plant

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Obligate Long-Day Plant

Obligate long-day plant

Rudbeckia showing short day growth habit

Echinacea with short day growth habit

Echinacea growing with LD

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Lighting Strategies• Night interruption (NI)

• Predawn lighting

• Day-extension lighting

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Response of Coreopsis ‘Early Sunrise’ to Long-day lighting treatments

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Effectiveness of Night Interruption Treatments on Campanula carpatica

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Sensitivity of Campanula carpatica to Low Light Levels

0 0.25 0.5 5 10 footcandles

Comparison of commonly used electric light source in R/FR

Light sourceR/FR

Sunlight 1.15

High pressure sodium 5.9

Incandescent 0.7

Metal halide 3.3

Cool white fluorescent 8.8

Light Quality Is Influenced by Light Source

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Influence of Light Quality on Coreopsis grandiflora

Types of Photoperiodic Lighting

• Incandescent

• Fluorescent

• High Pressure Sodium

• Moving High Pressure Sodium

Incandescent

Bench Lamps Spacing Height

4 foot 60W 4 feet 2 to 3 feet

2-4 feet 100W 6 feet 2 to 3 feet

General rule - 1.25 Watts per square foot

Incandescent Installation at Post Garden’s in Rockwood, MI

500-watt quartz lamps 96 lamps per acre 15’ between lamps Rows of lamps spaced 60’ apart Lamps face both directions in each row Equals 1.1 W per square foot

36’

15

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15

15

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15

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60’ 60’

Incandescent Installation at Yoders - Alva, Florida

150 watt bulbs with internal reflector 10’ x 10’ spacing 8’ to 9’ above soil Equals 1.5 W per square foot while on 5 minutes on/5 minutes off for 4 hours Equals 0.75 W per square foot continuous

duty

Fluorescent Installation at Yoders - Pendleton, South Carolina

75-watt CWF, 8’ tube 10.5’ x 10.5’ spacing 8’ to 9’ above benches Equals 0.75 Watt per square foot 4 hours on winter and 2 hours summer

High Pressure Sodium

0.3 Watts per square foot 1500 square feet per 400 W fixture (theory) Equals 40 x 40 spacing … but 45’ high

High Pressure Sodium Installation at Bordine’s Better Blooms, Clarkston, MI

5 lamps in a 30’ x 150’ house (4,500 sq ft) Lamps 13’ from end walls, spaced 25’ 0.5 watts per square foot 15 fc in all corners 30 to 35 fc under lamps

Lighting system over perennials

Moving High Pressure Sodium

Attach lamps to a boom

Cycle boom back and forth every 30 minutes or less

Moving High Pressure Sodium Installation at Center Greenhouse, Denver, CO

Two 1000-watt lamps on a boom 35’ x 275’ house (6125 feet) 0.35 Watts per square foot (equivalent) 700 fc under lamps, 150 fc on edge Round trip every 16 to 18 minutes

High Pressure Sodium Moving Boom Installation at Mid-American Growers, Granville, IL

Lighting Costs

• Watts per square foot times electrical rate per KWH equals cost per 1000 square feet per hour

• Watts X $ per KWH = cost per 1000 ft2

ft2 Hour

Electrical Cost per 1000 ft2

Watts per ft2 Cost per night

1.25 $0.11

1.1 $0.09

0.75 $0.06

0.5 $0.04

0.35 $0.03

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Points to Remember• Night interruption or day-extension lighting

is more effective than predawn lighting for inducing flowering

• For rapid and uniform flowering, night interruption should be four hours long with lights on the entire four hours

• In most perennials, provide at least 10 footcandles to induce flowering

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Points to Remember• Standard mum lighting is adequate to induce

flowering in many perennial species• Cool white fluorescent, high pressure sodium

or metal halide lights are also effective and will result in more compact plants for some plant species

QUESTIONS?