Greenhouse Management

Light

2162Adam Nash

PHOTOSYNTHESIS

CO2 + H2O + Light Energy C6H12O6 + O2

•Complex Carbohydrates•Proteins•Fats

•Takes place in the Chloroplast

Light Quality

• Visible Wavelength– Visible light is between ~ 400 - 700 nm

• Wavelength vs. Energy

Shorter Lower

Longer Higher

Light Spectrum

Photosynthesis Uses Mostly Blue and Red light (reflects green) Visible Light

• Violet• Blue• Green• Yellow• Orange• Red

Light Intensity 3,000 foot-candle will saturate most

greenhouse plants 10,000 foot-candle needed to saturate

lower levels of canopy Midwest Light Levels

• 10,000 summer midday• 500 winter midday

Maximizing Light Intensity Metal framework Wider frame spacing Paint wooden frames white Choice of covering material Clean glass Wider plant spacing

Supplemental Lighting To increase light intensity To control photoperiod

Moving Supplemental Lights

Types of Lights Incandescent

• High heat, low efficiency, high red, low blue Fluorescent

• Expensive, less heat, low power, high blue

Photoperiod Response of a plant to the day/night cycle Can measure a difference of 5 min in 24 hrs. Controls:

• Bolting in lettuce• Bulbing in onions• Tuber formation in dahlia• Poinsettia bract coloration• Flowering in Mum• Etc., etc., etc.

Did you see a commonality among the examples on the previous slide???

Reproduction

Plant Categories Short-day plants Long-day plants Day-neutral plants

Short Day Plants(long night plants)

Typically initiates reproductive behavior when day length drops below 12 hours

Long Day Plants(short night plants)

Typically initiates reproductive behavior when day length exceeds 12 hours

Modifying Day Length

To create a short day / long night• Example: Poinsettias• Use black-out cloth (note: a flashlight provides

enough light intensity to create a short night) To create a long day / short night

• Example: for vegetative growth on young mums• Turn on light for a few hours in middle of night

Adding Light Also Means… Higher Intensity Light

• High Photosynthesis Rate In Greenhouse High Intensity Light

• Higher Temperatures• Lower Humidity• Causes More Transpiration

Use More Water

Temperature Effects OnNet Plant Growth

When rate of photosynthesis exceeds the rate of respiration, net growth occurs

When rate of photosynthesis equals the rate of respiration, no growth occurs

When rate of photosynthesis is less than the rate of respiration, plant growth declines

(Cooler nights are used to reduce the rate of respiration to ensure net plant growth)