Greenhouse Management Light 2162 Adam Nash

PHOTOSYNTHESIS CO 2 + H 2 O + Light EnergyC 6 H 12 O 6 + O 2 Complex Carbohydrates Proteins Fats Takes place in the Chloroplast

Light Quality Visible Wavelength –Visible light is between ~ nm Wavelength vs. Energy ShorterLower LongerHigher

Light Spectrum

Photosynthesis Uses Mostly u Blue and Red light (reflects green) u Visible Light Violet Blue Green Yellow Orange Red

Light Intensity u 3,000 foot-candle will saturate most greenhouse plants u 10,000 foot-candle needed to saturate lower levels of canopy u Midwest Light Levels 10,000 summer midday 500 winter midday

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

Supplemental Lighting u To increase light intensity u To control photoperiod

Moving Supplemental Lights

Types of Lights u Incandescent High heat, low efficiency, high red, low blue u Fluorescent Expensive, less heat, low power, high blue

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

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

Short Day Plants (long night plants) u Typically initiates reproductive behavior when day length drops below 12 hours

Long Day Plants (short night plants) u Typically initiates reproductive behavior when day length exceeds 12 hours

Modifying Day Length u 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) u 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… u Higher Intensity Light High Photosynthesis Rate u In Greenhouse High Intensity Light Higher Temperatures Lower Humidity Causes More Transpiration u Use More Water

Temperature Effects On Net Plant Growth u When rate of photosynthesis exceeds the rate of respiration, net growth occurs u When rate of photosynthesis equals the rate of respiration, no growth occurs u 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)