by Ed Rosenthal
Plants can be supplied with CO2 by spraying them periodically with carbonated water or seltzer (salt-free soda water). CO2 enriched sprays are especially convenient to use with small plants, such as seedlings, rooted clones and small plants. This method is a bit expensive if you are buying soda water for large plants. Gardeners can lower the cost significantly by make their own soda spray by carbonating water using a kit.
VINEGAR AND BAKING SODA
When vinegar and baking soda are combined, they make a salt and release CO2.
The best method for creating a controlled release of CO2 is to drip vinegar into a solution made of baking soda and water. As the vinegar combines with the solution, CO2 is released. Regulating the frequency of the drip controls the amount of CO2 generated. This is not a cheap way to make CO2 in a mid-large size garden, because baking soda and vinegar are expensive to purchase in the quantities needed to create significant amounts of CO2.
To generate one cubic foot of CO2, combine 3 quarts of 5% vinegar with 3.7 ounces of baking soda. Generating one cubic meter of CO2 requires 101 liters of 5% vinegar and 3.7 kilos of baking soda.
This system is costly to operate and is only feasible for a small garden.
FERMENTATION
Fermentation is the process used to brew beer and make wine. To ferment alcohol and make CO2, all that is required is a jug or container, malt or another source of sugar, and yeast. Yeast are single-cell microorganisms that have been used in baking and fermenting alcoholic beverages for thousands of years. In fermentation, yeast digest sugar and release alcohol and CO2. A gross simplification of this process is:
C6H12O6 => 2(CH3CH2OH) + 2(CO2) (Sugar => Alcohol + Carbon Dioxide)
One kilogram of CO2 equals 0.546 cubic meter of gas.
As yeast feast on the sugars, they release about half the weight of the sugar as CO2, so one pound (0.45 k) of sugar yields about half a pound (0.23 kg), or 4.35 cubic feet (0.12 m3), of gas. The yeast complete their meal in about four days. Then the solution must be replaced.
BEER MAKING KIT
Yeast have a hard time processing sugar as the alcohol content climbs. Most beer yeast slow down as the liquid approaches about 5-8% alcohol. The maximum amount of sugar that yeast can process well is about 1⁄10 of the weight of the water. A gallon of water weighs 8 pounds (3.6 kg), so about 13 ounces (0.381 l) of sugar can be used. A liter of water weighs 1,000 grams, so use 80 grams of sugar.
ANIMAL RESPIRATION
Humans and other mammals, birds, and, to lesser extent, reptiles, produce a large amount of CO2 each day. The effect of each breath they take is CO2 released into the atmosphere. A human (150 lbs., 68 kg) produces an average of 0.9 kilograms CO2 per day. In an hour a human releases .326 cubic feet of the gas (0.0092 cubic m).
When placed near a garden, animals such as pet rabbits use the oxygen the plants produce and complete the cycle by returning CO2 to them. A precautionary note on keeping animals around plants: animals are constantly shedding and creating dander. Much of this material becomes airborne and easily attaches to sticky plant parts. Any garden air in proximity to animals should be filtered.
Green Pad CO2 Generators are made with a combination of carbons and acids and are activated when sprayed with water or when the humidity of the room rises above 35% (your room should already be well above this level). They last for a week and can be used to provide CO2 to grow rooms and clone domes.
USING CO2 OUTDOORS
Even plants grown outdoors can benefit from CO2 supplementation. They will grow bigger, sturdier, and produce higher yield. Plants grown in tunnels or in greenhouses also benefit from CO2 supplementation because they rapidly deplete the air of CO2 as they photosynthesize, so air enrichment is very effective at increasing their growth.
To enrich the air around a plant outdoors, run a CO2 line from a tank up the stem of the plant so that the gas disperses around the canopy. This works best when there is at most only a gentle breeze.
COMPOST PILES
Compost piles produce considerable CO2 and can be placed in the center of a densely planted outdoor garden. As the CO2 is emitted by the pile, breezes will carry it through the plants. A small compost container can be placed under a large plant. Because compost piles generate heat, the emerging gas will be warmer than the surrounding air and drift up through the plant’s canopy. Moist organic mulches or thin layers of compost can also be placed over the soil. When they are provided with a bit of nitrogen, the microorganisms they hold become very active and release extra CO2. Their activity is regulated by temperature, so they produce more CO2 during the warmer daylight hours, rather than at night.
Compost can be used to increase the CO2 content of both outdoor and greenhouse gardens. It is not necessarily smelly and yields a large amount of CO2. Using compost or vermicompost (compost with worms) to generate CO2 is environmentally friendly. When it is ripe, the compost can be used to enrich the soil or to make compost tea.
About 1⁄6 to 1⁄4 of the compost pile’s starting wet weight is converted to CO2, so a 100 pound pile contributes 33-50 pounds (15-22 kg) of carbon to the gas. Carbon makes up about 27% of the weight and volume of the gas and oxygen makes up 73%, so that the total amount of CO2 created is 61 to 93 pounds (27.6 kg-42 kg), produced over a 30-day period. That comes to two to three pounds (0.9-1.3 m) or 16-25 cubic feet (0.45-0.7 cubic m) a day. Similarly, for each 100 kilograms of starting matter, the pile releases 60-90 kilograms of CO2 over a 30-day period. The gas is supplied both day and night, so much of it is produced when the plants won’t utilize it.
ASK ED: Marijuana Questions
CO2 OXYGEN DISPLACEMENT
You recommend CO2 as a boon to plant production when growing under indoor lights. You also mention that CO2 is not good for the root zone as it displaces the needed O2 used by the roots to “burn” the sugars and build the roots. So is there a conflict with upping the CO2 content of a room and promoting healthy root development? Would a supplementary system of oxygen distribution (with tanks) be of benefit in such an instance?
The amount of CO2 found in the air is about 375 parts per million (ppm), or .0375%, almost 4/100 of 1%. A CO2 enriched garden might have a CO2 content of 1500 ppm, or .15%. In contrast, oxygen comprises about 21% of air’s volume. The increased amount of CO2 in the air has little if any effect on the amount of oxygen absorbed from the water.
At the air-water surface, water releases CO2 to the air and picks up oxygen. That is why it’s recommended that reservoirs (and fish tanks) keep the water circulating. The more the water circulates and comes in contact with air, the more it releases CO2 and holds oxygen. Even in a CO2-enriched room, the water releases CO2 in favor of O2.
Adding O2 to the roots using a tank is a good idea. Enriching the water or the soil helps maintain a healthful environment for the roots. Roots enriched with oxygen are healthier, grow faster and are more efficient at absorbing nutrients.
Adding a heavy layer of organic compost or mulch on top of the soil provides both a bit a warmth and protection from the elements and at the same time increasing the CO2 content around the plants as microorganisms feed on it, releasing the gas.
CO2 AND ROOTS
Roots do not use CO2 because they don’t photosynthesize, so they have no use for it. Plants obtain CO2 for photosynthesis through the leaf stomata. In fact, CO2 in the soil or water can pose a problem, because it can drive out much-needed oxygen.
CO2 and O2 both dissolve in water and compete for a place in the solution. In this respect, gardeners and aquarium enthusiasts face a similar problem. In fish tanks, pumps keep the water circulating so that the water at the surface releases the excess CO2 produced by the fish and dissolves free O2, maintaining the dynamic balance of oxygen saturation that the fish need to survive.
When soil, planting mix, and such hydroponic mediums as rockwool or coir are watered with CO2 water (seltzer), the dissolved CO2 eventually returns to its gas form and forces oxygen from the soil’s air spaces. Then the roots are star
ved of oxygen, which they need for respiration.
Some gardens are divided to create a room of vegetating plants and a room of flowering plants. The GroZone Dual Zone Controller allows the gardener to control two different spaces at the same time and includes settings for low and high CO2.
OXYGEN
Oxygen is not just a byproduct of photosynthesis; it is also used by the plant. The mitochondria, the cells’ energy centers, use oxygen as they burn sugar to power growth and flowering, which produces water and CO2 as byproducts.
A plant has three sources of oxygen: the oxygen it releases during photosynthesis but holds in its structure, the oxygen in the atmosphere, and oxygen dissolved in water, which the plant roots absorb. Oxygen comprises about 21% of the air solution, so plant parts above ground rarely experience a shortage of it.
Another way of supplying plant roots with oxygen is by producing it using electrolysis. Electrolysis is the process of separating water into its component parts: hydrogen and oxygen by running an electric current through it.
Roots require oxygen for respiration. They obtain it from air spaces in the soil or from oxygen that is dissolved in water. When roots don’t have enough oxygen, they deteriorate in various ways. They cannot draw up water and nutrients effectively, so root growth and respiration stops. They lose their stamina and become susceptible to pathogens. Anaerobic (oxygen-free) conditions also promote growth of harmful anaerobic bacteria that thrive in oxygen-free environments. They produce ammonia, which is toxic to plants at high levels. An ammonia smell is a sure sign of anaerobic conditions.
For roots to have adequate oxygen supplies, the planting medium must not be packed too tightly and must have porosity, so that it has space to hold air as well as water.
In hydroponic systems water should be circulated and aerated to remove the CO2 and replace it with oxygen. Water can be supplemented with oxygen by adding a small amount of hydrogen peroxide (H2O2) to the water.
Warm water holds much less oxygen than cool or cold water, as discussed in the the Temperature, Humidity and Air Quality chapter.
Porous soil that allows air to circulate through the root area is not the only way your plants can get the oxygen they need to thrive. Some gardeners supplement the water they use with extra oxygen to deliver the maximum amount to roots. How much oxygen roots can use is not certain, but experiments with both cuttings and rooted plants of several types all demonstrate that an oxygen-enriched environment makes a big difference in plant vigor—in the range of 50-60% more growth for cuttings and 30% for rooted plants. Conversely, water with a low dissolved-oxygen concentration inhibits growth. Temperature affects the oxygen level of the water. The warmer the water, the less oxygen it can dissolve.
Water can be enriched with oxygen in several ways. The best source of naturally enriched water is immediately downstream from a waterfall. This could be the drop of water into the reservoir from a table. An inexpensive aquarium air bubbler or a submersible pump circulates the water in reservoirs and water tanks so new water is constantly coming to the surface to exchange gasses with the air.
Indoors and out, hydrogen peroxide (H2O2) can be used as an oxygenating supplement. Add one part of 3% hydrogen peroxide (H2O2) (drugstore strength) for every ten parts of water. The extra oxygen will dissipate in 72 hours or less. At a higher concentration H2O2 kills bacteria and fungi in the water and soil, and is useful if you are combating pathogenic fungi or bacteria, but remember that healthy soil contains many helpful bacteria, too.
SOUR DIESEL
WATER
Not all water is created equal. When we drink different waters, we experience their distinctive qualities as different flavors. The mineral, carbon dioxide, and oxygen content of water vary substantially, and affect your plants. Three key measures of water composition are its alkalinity, its pH (alkaline-acid level), and its content of dissolved minerals. Mineral content is often referred to as dissolved solids, which are expressed as parts per million (ppm) and can be tested approximately by measuring the electrical conductivity (EC) of the water.
Alkalinity is the ability of the water to buffer acids. When water contains dissolved solids, usually calcium (Ca) and magnesium (Mg), its pH is not affected as much by the addition of acidic substances, such as a soluble fertilizer. The Ca and Mg buffer the acid/alkaline balance so that small additions of fertilizers don’t create dramatic changes in pH. When water is very pure and contains no minerals, it is called soft water and has little or no buffering ability, so its pH is very changeable. Adding a small amount of an acidic substance has extreme effects on soft water’s pH.
Waters from different areas vary dramatically in the amount of dissolved solids they contain and, consequently, in their buffering ability. For example, tap-water in San Francisco, California contains about 65 ppm of dissolved salts. It has very little buffering ability. By contrast, water in Los Angeles, California contains about 450 ppm. This “hard water” has very strong buffering ability, so it takes a large amount of pH adjuster to have much of an effect.
Water districts and companies continuously test the water they supply you. The test results are public records and are available from the water district or company. The results may be sent to customers annually or posted on the Internet. If not, they can be obtained by communicating with the water supplier. In addition to measures of alkalinity, dissolved solids, and pH, the report shows contaminants.
A reading of 125-150 ppm for your water is a good starting point because it represents some buffering ability, but not so much that large amounts of minerals have to be added to adjust pH. To increase the reading use Cal-Mag, which contains a solution of calcium and magnesium, or alternatively, calcium nitrate (CaNO3). To lower the mineral level in the water, use a reverse osmosis system or a charcoal/chemical de-ionizer. The high-mineral water can be mixed with the purified water to get to the desired 125 ppm.
pH
The pH is a measure of acid-alkalinity balance. Technically, it represents the concentration of hydrogen or hydroxyl ions in a solution. pH is measured on a scale of 0-14, with 0 the most acid, 7 neutral (an equal concentration of hydrogen and hydroxyl ions), and 14 pure alkali. This is a logarithmic scale, so every one point increase or decrease in pH reflects a 10-fold change in acidity or alkalinity. For example, a pH 5 solution is 10 times more acidic than a pH 6, while a pH of 4 is whopping 100 times more acidic than pH 6! Most nutrients the plants use are soluble only in a limited range of acidity, from about 5.5 to about 6.5 in mineral soil and 5.6 to 6.4 in a hydroponic medium. Solubility also depends to some extent on the type of soil, planting mix, or hydroponic medium.
Should the water or the water-solution in the soil become too acid or alkaline, the nutrients dissolved in the water precipitate and become unavailable to the plants. When the nutrients are locked up, plant growth is slowed. Typically, a plant growing in an acidic environment with a low pH is very small, often growing only a few inches (approx 7.5 cm) in several months. Plants growing in a high-pH environment look pale and sickly and also have stunted growth.
The pH of tap water may change seasonally. Test it regularly. The pH of tap water changes when your local water company flushes its system, so it is a good idea to check it every time.
The pH of water can change for many reasons. Plants affect the pH of the water solution as they remove various nutrients. Microbes growing in the medium also change the pH. Addition of nutrients by the grower changes pH, as well. For this reason, growers check and adjust the pH frequently.
For absolute control of a planting medium system, test the pH weekly. Carbon seed mediums have a lot of buffering ability and adjust to pH changes.
Plants growing in hydroponic systems have more effect on the pH of the water/nutrient solution, so it should be checked every day or two. Adjust pH after nutrients are added, since they affect its balance. Measure the pH of water using a pH meter or chemical reagent test kit designed for aquariums or gardens. Meters are the easiest to use.
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nbsp; Once the water is tested, it should be adjusted if it does not fall within the pH range of 5.8-6.3. Adjust the water using small increments of chemicals. Once there is a standard measure of how much chemical is needed to adjust the water, the process becomes fast and easy to do. Hydroponic supply companies sell measured adjusters, pH UP and pH DOWN, that are very convenient and highly recommended. The water-nutrient solution can also be adjusted using common household chemicals. Water that is too acidic can alternatively be neutralized using potassium bicarbonate, or wood ash. Water that is too alkaline can be adjusted using nitric acid, sulfuric acid, citric acid (Vitamin C), kombucha tea or vinegar.
Optimum water pH in a hydroponic system is 5.6-6.3. In a soil system the pH should be between 5.8-6.5. Different nutrients can require a different pH, so you should always check the bottle.
Chlorine is added to water systems to kill infectious agents, but when the water is used for irrigation, the chlorine kills some of the beneficial microorganisms in the rhizosphere, the area surrounding the roots. To protect the micro-life, remove the chlorine from the water.
In the past, water was treated with a chlorine compound that had a characteristic odor and taste. This chlorine evaporates when tap water sits for a day or two. Now, most water systems use chloramine, which doesn’t evaporate. Instead, it has to be removed.
Aquarium hobbyists face the same problem because the chemical also affects fish. They use an additive that removes not just chlorine but the ammonia which is produced by the chemical reaction.
Chloramine can also be removed from water by adding a gram of vitamin C (ascorbic acid) per 75 gallons (285 l) of water. Adding ascorbic acid to the water is safe for both the plants and you.