Notes for 3/21/00

On handout #2, schedule based on planting outside 6/1

 

Jaderloon - top greenhouse construction company in world.  www.jaderloon.com

 

Lighting for Plant Growth by Bicknell

            very good book on plant lighting

 

*****

Lighting

High pressure mercury lamps

            Has spectrum similar to fluorescents

            Distinctive  bluish light

            Efficiency rating of about 13% of electricity used is given off as light

            Available in power ratings up to 1000 watts

High pressure metal halide lamps

            Up to 2000 watts

            Available power rating is 20% of electricity used

            Cost more than mercury lamps

            Output deteriorates over time faster than other lamps

            Excellent spectral output

            Doesn't give "funny" color to plants

                        Good for retail areas

High pressure sodium

            Most widely used in US

            Cheaper than mercury lamps

            Wide spectrum

            Light concentrated in yellow-orange part of the spectrum

            Maximum efficiency is 25%

            400 and 1000 watts

            Up to 24,000 hour lifespan

                        Compare with 10,000 hour lifespan of mercury)

Low pressure sodium

            Available in 35 to 180 watts

                        180 watts best for greenhouse

            Most efficient of all lamps = available power rating of 27%

            Life expectancy is 18,000 hours

            Less heat than from other lamps

                        Can be placed closer to plants

            Has limited spectrum and not suitable for some crops

            Pure yellow light

            Causes pale green color in lettuce, petunias, African violets

            Also low blue levels: morphological changes (ie strap-shaped leaves in lettuce)

            These problems can be cured by adding 10% light from incandescent or the sun.

 

Photoperiod (see handout #4)

Flowering is controlled by light

Hortocultural crops are classified according to their response to photoperiod = each photoperiodically sensitive plant has a critical night length

1.  Short day plants = nnyctiperiodism - flowers only when critical night length has been exceeded

            eg cattleya, orchids, kalanockoe

2.  Long day plants = hemeroperiodism = flowers only when the dark period is shorter than the critical night length

            eg tuberous begonia, hibiscus species, spinach

3.  Day neutral - flower reguardless of night length

            but do need enough light for photosynthesis

            eg African violets, roses

4.  Quantitative long day plants = partial hemeoperiodism

            Initiate flower buds under any day length, BUT

                        time to flowering is shortest when critical night length is not exceeded = long day response

            eg carnations, salvia

5.  Quantitative short day plants = partial nyctiperiodism

            initiates flower buds under any day length, but faster when critical night length is exceeded = short day response

            eg cosmos, zinnias, cinerarias

                        (cosmos: 15.5 hours for 2 weeks to initiate flower buds)

6.  Quantitative temperature & photoperiod interaction

            Plants are short day or long day or day neutral at one temperature but different response at another temperature

            eg snapdragons, petunia = quantitative long day at high temperatures, but day neutral at lower temperatures.

            eg poinsettia is short day at high temperatures and long day at low temperatures.

 

Basically photoperiod control comes in  forms

1.  Short night treatment

            lengthening the day period with artificial lights

            a.  prevents flowering in short day plants

            b.  promotes flowering in long day plants

            Lights are turned on at the end of the day or in the middle of the night

            If you have a short day plant like chrysanthemum with a critical night lenght = 9.5 hours

            You want to prevent flowering but you have a 9 hour day and 15 hour night

            Option 1: turn lights on at dusk and light the plants for 6 hours = 9 hours night yields vegitative growth

            Option 2: Apply 2 hours of light 4 hours after dark = 9 hours day + 4 hours night + 2 hours "day" + 9 hours night.

                        --no one night period exceeds the critical night length

 

The required light intensity to get a plant response is very low

            minimum for photosynthesis is 3-4 watts/square meter

            Minimum for photoperiod contron is 0.02-0.09 watts per square meter

            The light from one street lamp can screw you up!

For a 4 foot wide bench

            One string of 60 watt bulbs, 4 feet apart

            Not more than 5 feet above the soil level

            Run down the middle of the bench

Two benches can be lighted by

            1 string of 100 watt bulbs

            6 feet apart

Flash lighting or cyclic lighting

            As little as 1 second of light at 0.2 to 0.4 watts per square meter

            Flash every 5 seconds

            Will prevent flowering

            This requires special switches!

The second type of photoperiod control = long night treatment

            If you want to initiate flower buds in chrysanthemums in mid summer

                        Nights are too short

                        Critical night length of 9.5 hours is not exceeded

                        Use a black cloth pulled over bench

                        For every forgotten day when you didn't do the black cloth = 1 day delay in flowering

                        Can also put in closet (cover cracks to assure it is truly dark)

Gasses

What are the components of unpolluted air?

·        Nitrogen (N2)                           78.09%

·        Oxygen (O2)                             20.94%

·        Argon                                       0.93%

·        Carbon dioxide (CO2)              0.038% (380 parts per million-ppm)

·        Misc                                         0.01%

·        Moisture                                   1-3% by volume

CO2 is the third most abundant gas in the air

·        Air around highly industrialized areas may be as high as 500 ppm, due to the combustion of coal, gas and oil

·        Global greenhouse effect: CO2 traps heat energy, and as the CO2 levels in the air rise, the global temperature may rise

o       This is, as yet, scientific conjecture, with few facts to back it up.  Though there is a warming trend, it may be that the warming trend is just a continuation of that trend which began during the last ice age (and unrelated to changing CO2 levels in the atmosphere.

·        CO2 is required for photosynthesis.

·        It is one product of respiration

·        300 ppm is adequate for plants

o       up to 2,000 ppm will increase photosynthesis

o       >5000 ppm is the maximum tolerated by humans (or it causes blood acidity problems)

·        Most common CO2 enrichment for greenhouses

o       1000-1200

o       vents must be closed or the CO2 will be vented out!

o       2 inch open vent will negate CO2 enrichement because it will all leak out

o       Increased CO2 will require

§         change in fertilizer patterns (especially N, P, K) due to faster plant growth

§         change in light levels: may need supplemental light to take full advantage of the CO2

Handouts

·        Greenhouse & Nursery businesses in Alaska

·        Seedling dates

·        Measuring the light (converting photographic readings to foot-candles)

·        Critical night length chart

·        Unvented Kerosene Heaters--Ok for Greenhouses

·        CO2 levels in an unvented, unenriched greenhouse; CO2 vs light vs photosynthetic rate

 

The current copyright laws protect this page, even though not specifically copyrighted.

However if you want to use portions of it feel free to do so, though I would appreciate it if you would acknowledge my authorship.

ß Ray's Home