Plants and Carbon Dioxide

People laughed when it was claimed that playing music to plants made them grow better. It really did because the sound vibrations actually strengthen the stem fibres, shorten the internode length, and cause stress growth reactions from the plants.

Then people laughed when it was claimed that singing to plants made them grow better. However, it is true. The CO2 from human breath actually makes plants grow faster. If you and a few gardeners stay in the indoor garden area during the light period, the plants would do very well.

It is thought that the massive plants that developed millions of years ago had
lived an environment with much more carbon dioxide in it. In their
evolution, the plants still maintained the capacity to use much more carbon dioxide than the world has now.

Luckily in the smoggy cities, the CO2 level can be as high as 500 PPM, and by just having a good circulating fan, the plants should have enough CO2 for a medium-light indoor garden.

A high-light indoor garden with the carbon dioxide amount increased from an ambient level of 300 PPM to a high level of 2,000 PPM can nearly double plant growth.

Why All Plants Need CO2

The dry matter in a plant is 90% carbon, hydrogen, and oxygen. All the
carbon has to come from the carbon dioxide (C02) in the air.

CO2 molecules are only necessary during the light times. Plants do not need CO2 in the dark period, and in fact plants breathe out CO2 all the time, just as humans do. The slight difference is that in the light period, leaves use up their own CO2 to make sugars and so appear to breathe out only oxygen in the daytime.

The more light available to a plant, the more CO2 it needs for photosynthesis. Experiments have shown that during photosynthesis, it takes about 1 a photons to make enough electrons to create sufficient energy to split one CO2 molecule into carbon (c) and oxygen (02) atoms and form a sugar. There are trillions of photons striking the plant leaves, so a grower must provide enough CO2 or else the photons will just bounce off the leaves without doing much.

A plant in full Sunlight (about 5,000 lumens per square foot) could process about 2,000 PPM of CO2 if it was made available in a greenhouse. Outdoor CO2 is nowhere near that. Indoor gardens with the light level at 3,000 lumens per square foot need about 1,500 PPM of CO2 for the limited light. With the level at 1,000 lumens per square foot, only about 300 PPM of CO2 is required - which is less than ambient air (city air normally has 400 PPM of CO2), The lower the CO2 level, the more the air has to be kept moving past the leaves.

Remember that it is the PAR value (not lumens) that indicates the plants' use of CO2 because the light that the leaves cannot sense is totally wasted and does not go down the photon funnel to be used for splitting CO2 into sugar.

How Much Carbon Dioxide Can Your Indoor Garden Use?

Experiments have shown that plants can handle up to 10,000 PPM of CO2 with no ill effects. At very high light densities, indoor plants have a maximum CO2 uptake of just over 2,000 PPM.

Light intensity increases with closer distance, so the CO2 level around plants needs to be increased respectively:

Lights Distances CO2 Needed for
from Plants Sugar Production
HID Lamps 4ft (120 cm) * Ambient
3 ft (90 cm) 400 PPM
2ft (60 cm) 1,000 PPM
1 ft (30 cm) 2,000 PPM

This is with maintaining all plant resources at MAXIMUM and at a temperature NOT EXCEEDING 30°C (86°F).
* Ambient CO2 in the cities is between 400-500 PPM.
* Ambient CO2 in the country is about 300 PPM.

Note: Any time your indoor garden temperature goes above 30°C (86°F), start shutting down the CO2