Article 2-3 Effective Use of CO2

Good gardeners say great things about C02. There’s no question that increasing carbon dioxide levels in the garden has tremendous potential for creating faster, more productive crop plants. The trick is to use C02 wisely-knowing when and how to add C02 for maximum results.

The first step is to create such great growing conditions in your garden that your crops will benefit from extra carbon dioxide! Careful attention to light levels, temperature, air flow through the garden, exhaust fan capability, air intake, crop spacing and nutrient supply will result – in a first class garden with healthy, vigorous plants; ready and willing to take up and use extra C02 efficiently. Overheated, crowded and bug-infested plants are so busy just trying to survive that adding C02 would be wasteful. Whip your gardens into shape first-then plan when and where to add C02 to get the greatest benefits.

Our plants go through several growth stages during their lives seedling/cutting stage, transplant, green growth, transition (to flowering and crop production) and production stages. Each growth stage has its own “cultural requirements” seedlings need different light levels and fertilizer strengths than established crop plants, for example – and extra C02 is more useful during some growth stages than others. Generally, adding C02 helps the most during periods of rapid growth, but researchers have discovered some surprising and useful facts about carbon dioxide’s effect on specific stages of growth and how extra C02 early in a plant’s life brings unexpected benefits months later! And once again, it was a Canadian team of University researchers and commercial growers who broke new ground in effective uses of C02 enrichment.

Rooted Cutting/Seedling Stage

The Canadians discovered that adding C02 to plants at the seedling-rooted cutting stage – for about two weeks – produced two benefits: faster early growth and greater final crop yield, even without extra C02 during green growth or crop production! This is useful information for hobby gardeners since a little extra carbon dioxide for rooted cuttings and seedlings can help plants so much. If you use tall, clear covers over your baby plants, release a little C02 under the cover to raise the C02 levels to about 1500 PPM. Remove covers to let in fresh air after a few hours, and be sure plants have only fresh air (no extra C02) during dark periods. The two-week period leading up to transplanting is the most effective time for this C02 technique. If you are already using C02 for other purposes, try treating your ‘small fry’ with this proven growth and crop stimulator.

Transplant Stage

Adding carbon dioxide during transplanting stage is not recommended, since plants are adjusting to new growing conditions and can make do with regular C02 levels in the air.

Vegetative (green Growth) Stage

Once plants are ‘established’ in green growth stage (full light levels, full strength fertilizers, spreading roots and new top growth), it’s time to consider adding C02 to your rapidly-growing green plants. Your decision should be based on the length of time your crop will be in green growth, as well as an impartial evaluation of the garden’s growing conditions. Plants with a long green-growth period (30 days and more) would benefit from C02 enrichment, growing to the desired size more quickly. Growth hormone used along with extra C02 and increased food strength, results in faster, healthier green growth plants.

Long Day Crops

Some crops, called ‘long day plants’, produce their crops during summer, while continuing to put out new leaves and stems-tomatoes and roses are typical long-day crops which benefit from supplemental C02 right through green growth/crop production stages. These plants do not go through a separate transition stage like short-day crops, so additional C02 can be applied (during the light cycle) through the life of the plants.

Short-Day Crops

‘Short-day’ crops have a definite ‘transition’ stage before flower or crop production begins, affecting C02 applications. (Short-day plants produce green growth during spring and summer, and flowers and crop in autumn, responding to the longer nights by beginning crop production. Chrysanthemum and hardy hibiscus are examples of this category of plant). Since C02 is most useful when established plants are actively growing, shut off your tank until crops pass through this transition stage and save the extra C02 for use when crops begin producing flowers. Holding off on extra carbon dioxide while plants go through the transition from green growth to crop production should help keep plants bushy and compact while they decide what they’re supposed to do next and reduce ‘stretching’ problems so common to the early transition period. In fact, if your short-day crop has a history of stretching, cut off the extra C02 two weeks before the end of green growth stage.

Short-Day Plants

Once crops are ‘established’ into crop production stage (full light levels, full strength food, plants actively producing crop) resume C02 enrichment – if all goes well you could consider increasing the nutrient strength gradually for periods of maximum growth during this stage. As growth slows and crop is finishing up, cut back on C02.

After 7-14 days, your crops will tell you: how many plants are gaining from the extra C02.

How much it is helping your crop plants. You can reposition oscillating fans, add C02 airlines to more oscillating fans, or increase C02 flow rate if growth rate is uneven or some plants need more C02. Usually growers become very enthusiastic about adding C02 at this point, since they can see how it’s helping their gardens. If little or no effect on growth is seen, check growing conditions for limiting factors, high garden temperatures, poor air movement, bugs, disease or incorrect nutrient mix all interfere with C02 uptake and growth.

The disadvantages of this method are:

  • periods of high temperatures in the garden-with no air movement.
  • limited amount of C02 supplied to the garden.
  • excess humidity levels in garden.
  • questionable efficiency of this method


use two or more small generators for a large garden. They will provide more even distribution of carbon dioxide – and less concentrated heat build-up than a single large generator.

Although the C02 generators require planning and careful use, they are a much less expensive C02 source than the compressed C02 tanks. Growers can take advantage of our naturally clean natural gas, which contains low levels of sulphur- growers in eastern North America have to contend with natural gas containing high sulphur levels, which can be harmful to the garden. If crops are responding to C02 applications well, consider using applications of “Growth Plus” and increasing nutrient strength gradually to take full advantage of excellent growing conditions.