CO2 SUPPLEMENTATION FOLLOW-UP:
A very common question to me when lecturing or doing evaluations at commercial grow operations is “When do I supplement my grow chamber with CO2 and how much do I supply?” A great question. Supplementing with CO2 can indeed substantially increase the rate of photosynthesis when used correctly. This can result in increased yield. When not used correctly it can result in you wasting a substantial amount of money. Here is a quick overview of when and how to supplement with CO2.
GET ALL THE OTHER SET POINTS IN THE CHAMBER AT THEIR OPTIMAL LEVELS –
GROW MEDIUM MOISTURE LEVELS
The second thing to do is:
USE A QUANTUM METER – HOW MUCH LIGHT IS ACTUALLY BEING DELIVERED TO THE PLANT CANOPY?
Now comes the interesting part. There still is some variation as to EXACT levels of CO2 supplementation but after a lot of examination of current data I can suggest this as a good guideline:
Plant stage: Light intensity: CO2 level:
small seedling 100 – 350 micro moles 400 ppm (ambient air)
vegetative 350 – 600/700 micro moles 400 – 800 ppm
flowering 700 – 1400 micro moles 800 – 1400 ppm
THE most common issue I see (when it comes to lighting and CO2) is that most of the time light levels falling on the canopy are dramatically below what the grower assumes they are. That assumption leads to the addition of high levels of CO2 when actual light intensity at the canopy does not support those high levels. Wasted CO2 = wasted money.
If I look at the various graphs out there representing the relationship between light intensity and CO2 supplementation, I see a correlation that we can tweak into a “not exact but helpful” rule of thumb for you as a grower. Here it is:
IF ALL YOUR OTHER SET POINTS ARE OPTIMAL, MEASURE THE LIGHT LEVEL AT THE CANOPY IN MICRO MOLES PER METER SQUARED PER SECOND. IF THAT NUMBER IS 500 (APPROXIMATELY) OR LOWER – NO ADDED CO2 IS REQUIRED. ABOVE 500 YOU CAN SUPPLEMENT WITH CO2 AT A LEVEL APPROXIMATELY EQUAL TO THE LIGHT LEVEL NUMBER PLUS 100. FOR EXAMPLE – 800 MICRO MOLES USE APPROXIMATELY 900 PPM CO2 SUPPLEMENTATION. 1100 MICRO MOLES USE APPROXIMATELY 1200 PPM CO2 SUPPLEMENTATION.
The actual relationship is not quite that linear but this rule of thumb will get you pretty darn close and save you wasted CO2 money! Visually monitor your plants and adjust levels accordingly. If you choose NOT to supplement withCO2 there is no real benefit to running canopy light intensity levels above the (approximately) 650 micro mole range. There is some “fuzziness” in the light intensity to CO2 relationship in the 500 – 600 micro mole range that gives some “flexibility/fluidity” to the suggested optimal ranges.
The quality and quantity of your final product is greatly affected by the intensity of light you deliver to the plant canopy. Many other decisions you make during your grow procedure also depend on that light level – CO2 supplementation or not, EC/ppm of nutrient solutions, grow room temperature, relative humidity levels, frequency of watering etc. It is THAT important to know the PPFD at your plant canopy if quantity, quality and cost effectiveness are important to you. Quantum meters will run from about $300.00 into the thousands. If you don’t own one, see if you can borrow/rent one. Or talk with a reputable science resource that can assist you in your tuning efforts. You and your plants will be happy that you did!
YOU NEED TO KNOW WHAT YOUR PLANTS NEED TO GROW!
Prepared by: David O’Connor – Controlled Environment Agriculture science consultant for Blue Seal