co2 for indoor growing

Carbon dioxide (CO2) applications in indoor growing

A range of factors will affect CO2 concentrations and how quickly they will fall in rooms without ventilation. These include occupancy (the surface occupied by plants), crop density/population, light intensity, horizontal air movement, light penetration of the canopy. Generally, indoor grow rooms should undergo a complete change of air every fifteen minutes, since CO2 levels can drop within minutes. During the day, increasing CO2 concentrations in the grow room to levels higher than the naturally occurring 330ppm can undoubtedly increase growth rates and yields by over 30%.

However for this to happen, all the other growing conditions also need to be optimal and favorable to proper plant metabolism. Depending on which plants are being cultivated, the benefits can take the form of higher harvest weights and/or shorter crop cycles. CO2-enriched grow rooms can also enhance crop quality. For example, edible plants may have a richer nutritional content and more pungent aroma profiles with a longer shelf life.

Lower concentrations of CO2 can seriously impede plant growth and general health. In fact, a drop of 25% in natural CO2 concentrations can easily inhibit growth by over 50%

Factors to consider when adding CO2 to ventilated growing areas

Increasing the levels of CO2 in your grow room can prove challenging. Using air changes to cool and dehumidify grow rooms can seriously hamper attempts to enrich the air with CO2. In these cases, most of the money spent on CO2 enrichment will – as it were – float straight out of the window. CO2 enrichment in such ventilated grow rooms means considering the following:

  1. It is usually pointless to add extra CO2 in rooms that are ventilated constantly. The plants close to the injection point will be exposed to some extra CO2, but little or no significant increase in CO2 is likely to show up on the meter and virtually all of the CO2 will end up outside, where it will also contribute to global warming.
  2. Even though CO2 is a heavy gas, it does not settle close to the floor in a grow room. Well-built grow rooms should have horizontal air flow (e.g. oscillating fans) and that air movement alone will be sufficient to waft any lazy CO2 molecules up into the higher air strata. It is more efficient if the CO2 generator releases the gas at the opposite side of the extraction fans in the room. The CO2 controller (sniffer) should be positioned half-way between those two pieces of equipment, usually right in the center of the room.

To ensure significant exposure to higher CO2 levels, the thermostatic ventilation system needs to perform well enough to actually switch off for at least 10 minutes. During that off-time a CO2 concentration of no higher than 800ppm can be easily produced. Any level higher than that is very costly. Around 50% of the 30% extra return will actually occur at a concentration of 800ppm.

The law of diminishing returns also applies to CO2 enrichment: adding another 400ppm will yield a smaller result than the first increase. Bear in mind that over the course of a day, the plant will not have had 100% exposure to higher CO2 levels and less return should be expected. It is for this reason that CO2 enrichment is rarely used in grow rooms that are ventilated. That said, it is possible to use a small air conditioner to extend the period the ventilation off-times.

Closed room environment

The easiest way to get the full benefit of CO2 enrichment is in a closed grow room environment – that is, a grow room that uses air conditioning and dehumidifiers to control temperature and relative humidity levels, rather than ventilation to outside. Basically there should be no new air taken in during crop daytime. This is a more costly and energy-intensive approach, but it can guarantee higher levels of CO2 and really will enable the grower to enjoy higher crop yields.

A blue flame indicates complete
combustion and is pretty safe.
If the flame turns to red, orange and
yellow, incomplete combustion is
taking place and some unwanted
by-products are produced.
This is not safe!

Closed room gardens are equipped with air conditioners that provide total management of the garden temperature. Extra dehumidifiers are used to control relative humidity, especially at night when no cooling is active. Throughout the day, the air conditioning performs much of the dehumidification needed in the grow room. These climate-controlled rooms can retain all of the added CO2, which reduces the cost of providing it, and the constant exposure also maximizes returns. Even so, this approach still requires some extra supervision.

Using an unvented gas burner (propane or natural gas CO2 generator) in a closed room can be difficult. These generators rely on virtually complete combustion of the natural gas, producing heat, CO2 and water vapor. A blue flame (with most of the gases used but consult your burner manufacturers guidelines) indicates complete combustion and is pretty safe. If the flame turns to red, orange and yellow, incomplete combustion is taking place and some unwanted by-products are produced such as carbon monoxide, ethylene, methane or unburned gas.

All of these by-products are produced in very small quantity but in a closed room system they can build up to toxic levels for plants over the course of the day. There are many symptoms of such exposure: drooping leaves, stunted growth, necrotic dotting of the inter-venal area, yellow or orange leaf spots, dead root tips, leaf-margin burns and tip burns are a few examples.

One easy fix is to perform a small air change every hour or two. This is usually enough to lower any unwanted gas concentrations. This also replenishes oxygen levels in the room. Nonetheless regular supervision of the burner and the flame it produces is needed. An electric relay should be used to stop the production of CO2 during ventilation. Oscillating fans should not be directed at gas CO2 generator as air movement tends to interfere with the combustion process.

Daily checks should be performed to ensure a proper supply of gas to the system because if no CO2 is supplied in a closed room system, plant growth will come to a halt rapidly. Also, a CO2 monitor tends to de-calibrate over time. Physical shocks to the sniffing sensor can also skew the readings. These CO2 sensors (non-dispersive infra-red) will show higher values than the true levels if they are not properly calibrated. Contamination of sensor from fine mist foliar spraying or sulfur burning would also falsify the results and possibly damage the CO2 sensor.

Another unsuspected challenge with closed rooms is that EXTREME CLEANLINESS at all times is vital. If fungal diseases rear their ugly heads, a closed room system will mean they can spread very rapidly. The same applies to insect pests.

Environmental factors to consider

Plants generally benefit from enriched CO2 if steps are taken to maximize proper stomata functions (transpiration):

  • Temperature no higher than 86oF and no lower than 65oF.
  • Relative humidity (RH) between 40% (low temp) and 60% (high temp),
  • Good horizontal air movement. The plants shimmer and shake lightly once every 30 seconds. An exception to this is in lower than 40% RH, where reduced air speed is better.
  • The tighter the crop canopy, the more horizontal air flow is needed. Some air flow should also be directed at the lower part of the main stem.
  • Light intensity is essential. The more light available, the more the plant will absorb the extra CO2 and use it for photosynthesis.
  • Reduce the heat caused by light radiation (too close to canopy lighting) which tends to stress plants and reduce CO2 absorption.
  • Control medium salinity (EC in medium). Too high will cause nutrient burns and too low can cause deficiencies.

Stomata are small openings which regulate gas exchange between the leaf’s interior and the atmosphere. Air from around the leaves enters the leaf tissue through the stomata. Once inside, the molecules in the air will dissolve into the fluid around the inner plant cells.

Carbon dioxide is essential to the process of photosynthesis. Most plants grown indoors require a minimum CO2 concentration of 330 mg/l to enable them to photosynthesise efficiently.

The Importance of Adding CO2 to your Grow Room

Indoor gardeners are always looking for new and innovative ways to boost their yields. There is, in fact, a very simple way to maximise your yields and grow strong and healthy plants, and this is through the addition of CO2 to your grow room. But what exactly is CO2 and how does it benefit your plants?

What is CO2?

CO2, or carbon dioxide is what we expel when breathing, and what plants use to initiate photosynthetic functions. Plants actually ‘breathe in’ CO2 in the day, but give out CO2 at night.

Levels of CO2 are measured in PPM (parts per million), and ambient room levels are typically in the region of 300-400ppm. Assuming you have sufficient circulation in your grow room you should be able to achieve the atmospheric standard of 390 PPM. At this level, you should see plant growth similar to what you see in your garden.

If the CO2 levels drop below 200 PPM, your plants will stop growing.

It is understanding this behaviour that can really benefit your grow. If everything is being done correctly and you have a fine tuned system, then CO2 can be the one big difference in boosting your yields. Adding enhanced CO2 levels to your grow can significantly boost plant growth without having to change the way you grow.

If you are looking to accelerate the grow cycles of your crops consider adding additional CO2 to your grow room. Plant growth accelerates as you increase CO2 levels up to around 1,500 PPM. Growers have observed up to a 100% increase in grow speed at 1,500 PPM.

The Benefits of Adding CO2 to your Grow Room

The most important and obvious benefit to your plants is the significant increase in growth that will occur, especially if the potential of your set up has already been maximised.

In addition to this, if levels of CO2 can be maintained around 1000-1200ppm then you will be able to run your grow room at a higher temperature. This can be incredibly important with growers constantly struggling to keep temperatures down and avoid temperature stress to your plants.

CO2 During Vegetation

During the vegetative growing stage adding CO2 is the biggest way you can increase the rate your plants stretch, allowing your plant to grow with a lot more vegetative grow in a much shorter space of time.

CO2 During Flowering

When adding CO2 to your grow room, the flowering stage is the most important. Adding CO2 to your grow room, especially in the first 2-3 weeks of flowering, can kick start flower production and boost flower size significantly.

How to Add CO2 to your Grow Room

Using exhale CO2 bags are the natural and easiest way of adding CO2 to your grow room. The Exhale CO2 bag cultivates carbon dioxide 24 hours a day with no need to refill bottles or use expensive production units.

They work through photosynthesis – photosynthesis is the process by which plant leafs make carbohydrates. Sunlight, carbon dioxide and water are converted into carbohydrates and oxygen by the action of chlorophyll in the chloroplasts of the plant. Plants growing indoors under artificial light often lack enough CO2 to efficiently photo-synthesise. When plants are able to maximise the process of photosynthesis, the result is larger plants with larger yields.

The power lies in the mycelial mass inside the vented cultivator. This mycelial mass cultivates carbon dioxide and the one-way breather patch releases CO2 continually for up to 6 months.

Please note, that as CO2 is heavier than air, the exhale CO2 bag should be hung at the top of the grow room to deliver a shower of CO2 over your plants.

When adding CO2 to your grow room, the flowering stage is the most important. Adding CO2 to your grow room, especially in the first 2-3 weeks of flowering, can kick start flower production and boost flower size significantly.