Elevating carbon dioxide levels can increase growth speed a great deal, perhaps even double it. It seems that the marijuana plant evolved in primordial times when natural CO² levels were many times what they are today. The marijuana plant uses CO² for photosynthesis to create sugars it uses to build plant tissues. Elevating the CO² level will increase the marijuana plants ability to manufacture these sugars and plant growth rate is enhanced considerably. CO² can be a pain to manufacture safely, cheaply, and/or conveniently, and is expensive to set up if you use a CO² tank system. CO² is most usable for flowering, as this is when the plant is most dense and has the hardest time circulating air around its leaves. If your strictly growing vegetatively indoors, [transferring your marijuana plants outdoors to flower], then CO² will not be a major concern unless you have a sealed greenhouse, closet or bedroom, and wish to increase yield and decrease flowering time. For a medium sized indoor operation, one approach is to used CO² canisters from wielding supply houses. This is expensive initially, but fairly inexpensive in the long run.
CO² is cheaply produced by burning natural gas. However, heat and carbon monoxide must be vented to the outside air. CO² can be obtained by buying or leasing cylinders from local welding supply houses. If asked, you can say you have an old mig welder at home and need to patch up the lawnmower [trailer, car, etc.] For a small closet, one tank could last two months, but it depends on how much is released, how often the room is vented, hours of light cycle, room leaks, enrichment levels and dispersion methods. This method may be overkill for your small closet. It is generally viewed as good to have a small constant flow of CO² over the marijuana plants at all times the lights are on, dispersed directly over the marijuana plants during the time exhaust fans are off. Opportunities exist to conserve CO² , but this can cost money. When the light is off you don't need CO² , so during flowering, you will use half as much if you have the CO² solenoid setup to your light timer. When the fan is on for venting, CO² is shut off as well. This may be up to half the time the light is on, so this will affect the marijuana plants exposure times and amount of gas actually dispensed. Environmentally, using bottled gas is better, since manufacturing it adds to greenhouse effect, and bottled CO² is captured as part of the manufacturing process of many materials, and then recycled.
Fermenting, CO² generators, and baking soda and vinegar methods all generate new CO² and add to greenhouse effect. CO² generation from fermentation and generators is possible. A simple CO² generator would be a propane heater. This will work well, as long as the gases can be vented to the grow area, and a fan is used to keep the hot CO² [that will rise] circulating and available below at the marijuana plants level. Fire and exhaust venting of the heat are issues as well. A room that must be vented 50% of the time to rid the environment of heat from a lamp and heater will not receive as much CO² as a room that can be kept un-vented for hours at a time. However, CO² generators are the only way to go for large operations. Fermentation or vinegar over baking soda will work if you don't have many vent cycles, but if you have enough heat to make constant or regular venting necessary, these methods become impractical. Just pour the vinegar on baking soda and close the door, [you lose your CO² as soon as the vent comes on].
This method leaves a great deal to be desired, since it is not easy to regulate automatically, and requires daily attention. It is possible however, to create CO² by fermentation, let the wine turn to vinegar, and pour this on baking soda. It's the most cost-effective setup for most closet growers, for whom expensive CO² equipment is a bit much to swallow. In fermentation, yeast is constantly killing itself; it takes a lot of space. You need a big bin to constantly keep adding water to, so that the alcohol levels will not rise high enough to kill the yeast. Sugar is used quickly this way, and a 10 pound sack will last about two to three weeks. This is also difficult to gauge what is happening as far as amounts actually released. A tube out the top going into a jar of water will bubble and demonstrate the amount of CO² being produced. Try sodium bicarbonate mixed with vinegar, 1 teaspoon [30cc] this will gush up all frothy as it releases CO² . do it just before you close the door on your cannabis plants. A MUCH cheaper way to provide CO² is 2 ounces | 55 grams sugar in 2 liters of water in a bottle [sterilized first with bleach and water, then rinsed], plus a few cc urine [!] or if you insist, yeast nutrient from a home brewing supplier. Add a brewing yeast, shake up and keep at 70 ºF | 25 ºC . Over next two weeks or so it will brew up about 1/2 once | 15 grams CO² for every ounce sugar used. Keep a few going at once, starting a new one every three days or so. With added CO² growth is phenomenal.
We measured 15 inch | 38 cm growth in eight days under a 250watt HPS bulb [tubular clear], Horizontal mount. A good container is a 1 gallon | 3.5 liter plastic milk jug, with a pin-hole in the cap. Also, the air-lock from a piece of clear tube running into a jar filled with water will keep microbes out and demonstrate the fermentation is working. A variation is to spray seltzer water on the marijuana plants twice a day. This is not recommended by some authorities, and receives great raves by people who seem to feel it has enhanced their crop. It stands to reason this would work for only a small un-vented closet, but may be right for some situations. It could get expensive with a lot of marijuana plants to spray. Use seltzer, not club soda, since it contains less sodium that could clog the marijuana plants stomata. Wash your marijuana plants with straight water after two or three seltzer sprays. It's a lot of work, and you can't automate it, but maybe that's good! Remember, being with the marijuana plants is a beautiful experience, and brings you closer to your spiritual self and the earth. Seltzer is available at most grocery stores. Club soda will work if seltzer water is not available; but it has twice as much sodium in it. A very diluted solution of Miracle Gro or Formula Flora plant food can be sprayed on the plant at the same time. One factor of using seltzer water is it raises humidity levels. Make sure your venting humidity during the dark cycle, or you could risk fungus and increased internode length.
Don't spray too close to a hot bulb! Spray downward only, or turn off the lamp first. Even though CO² enrichment can mean 30 to 100% yield increases, the hassle, expense, space, danger, and time involved can make constant or near constant venting a desirable alternative to enrichment. As long as the plant has the opportunity to take in new CO² at all times, from air that is over 200 ppm [parts per million] CO² , the marijuana plants will have the required nutrients for photosynthesis. Most closets will need new CO² coming in every two or three hours, minimum. Most city's will have high concentrations of CO² in the air, and some growers find CO² injection unnecessary in these circumstances. Some growers have reported to High Times that high CO² levels in the grow room near harvest time lower potency. It may be a good idea to turn off CO² 2 weeks before harvesting.
You have to vent a lot with a HID lamp, less so for fluorescent's. Also, humidity build up requires that you vent at least a few times per day. For a room with a hot lamp that builds up heat quickly, the best vent would be one that cleared the room in 5 minutes, then would stop for 25 minutes before venting again, or similarly, vent 3 minutes, shut off 12 minutes, etc. The trick is to find a timer that will do this sort of thing. Not easy to find and not cheap. Once you need to regulate CO² on and off inversely with the fan, your looking at a expensive climate controller. Alternatives are a thermostat that turns on a fan when a certain temperature is reached, and turns it off when the temperature recedes 40 °F | 4 °C . But it is a bitch to coordinate CO² release with this one, since you don't know when the fan goes on. But to sync it to CO² with a voltage sensing relay is the ready-made switch, so then the environment controller is cheaper. All you really want is a fan that clears the air in a few minutes, a temperature switch that turns on and off the fan, and an inverse switch that turns off and on the CO² . If you can vent the room really quick and the heat does not build up too quickly, the CO² could be run in a slow, continuous fashion, and would build up in-between the occasional quick exhaust cycles.
Two timers synced can be used, but the only ones cheaply available are the 30 minute interval, 48 trips per 24 hours. So you could have a fan run 30 minutes on, then 30 minutes off. You could also sync it to the light so that you don't vent when the lamp is off. You can sync this to an identical timer that will turn on CO² during the time that the fan is not on, and vise versa. It would be difficult to sync them closer that 5 to 10 minutes, but at least there would be a possible inexpensive solution. Fans are expensive to buy for venting, but you can just go down to the local electronic parts liquidators and they have muffin fans, so that's a real saving. These fans cost more new at the indoor garden stores. A good vent fan will keep the humidity and temperature down, and distribute CO² to your plants from new incoming air. Internal air movement is very necessary as well. An oscillating fan should be used to circulate air within the growroom, to help circulate CO² . It will also keep the humidity down, allowing the air to absorb more moisture, and reduce risk of fungus. A wall mount oscillating fan will not take valuable floor space. The best grow rooms have the most internal air circulation.
Proper temperature is one highly variable factor. Most books state optimum grow temperature to be 70 to 80 °F | 21 to 27 °C , but many list extenuating circumstances that allow temperatures to go higher. Assuming genetics is not a factor, plants seem to be able to absorb more light at higher temps, perhaps up to 90 °F | 32 °C . High light and CO² levels could make this go as high as 95 °F or increased growth speed.* An optimum of 95 °F degrees | 35 °C is new data that assumes very-high light, CO² enrichment of 1500 ppm [parts per million] and good regular venting to keep humidity down. It is not clear if these temperature will reduce potency in flowers. It may be a good idea to reduce temperatures once flowering has started, to preserve potency, even if it does reduce growth speed. But higher temperatures will make plants grow vegetatively much faster, by exciting the plants metabolism, assuming the required levels of CO² and light are available, and humidity is not allowed to get too high. With normal levels of CO² , in a well vented space, 90 °F | 32 °C would seem to be the absolute max, while 85 °F | 29 °C may be closer to optimum, even with a great deal of light available. Do not let the room temperature get over 95 °F degrees | 35 °C as this hurts growth. Optimal temperature is 80 to 86 °F degrees | 27 to 30 °C if you have strong light with no CO² enrichment.
Less than 70 °F | 21 °C is too cold for good growth. Low temperatures at night are OK down to about 60 °F | 15 °C outdoors, then start to effect the growth in a big way. Mid 50 °F | 10 °C will cause mild shock and below 40 °F | 9 °C will kill your plants with repeated exposure. Keep your plants warm, especially the roots. Elevate pots if you think the ground is sucking the heat out of the roots. This is an issue if you have a slab or other type of cold floor. As temperature goes up, so does the ability of the air to hold water, thus reducing humidity, so a higher average temperature should reduce risk of fungus. Contrary to many reports, high humidity is not good for plants except during germination and rooting. Lower humidity levels help the plant transpire CO² and reduce risk of molds during flowering. Studies indicate the potency of buds goes down as the temperature goes up, so it is important to see that the plants do not get too hot during flowering cycles.
Pests, molds and mildew
You really have to watch marijuana plant pests, or all your efforts could result in little or nothing in return. Mites and Aphids are the worst; whiteflies, caterpillar and fungi are the ones to watch out for long term. Pyrethrum bombs can start you with a clean slate in the room, and then homemade or commercial soap sprays will do most of the rest. When bringing in plants from outside, pyrethrum every broad leaf top and bottom and the soil too. Then watch them closely for a week or two, and soap down any remaining bug life you find from eggs being hatched. This should do the trick for a month or two, long enough it won't be an issue before harvesting. Fungus is another obstacle in the path of a successful growing season. When the flowers are roughly half developed they become susceptible to a fungus or bud rot. It appears that growing conditions for the fungus are best when temperatures are between 60 to 80 °F | 15 to 27 °C and the humidity is high. The fungus is very destructive and spreads quickly. It is a spore type of fungus that travels to other buds via the wind so it is impossible to prevent or stop if weather conditions permit it to grow. If things should go badly and the fungus starts to attack your plants.
Fungi can wipe your crop quick, so invest in some [SAFE] fungicide and spray down the plants just before flowering if you think fungus may be a problem. Don't spray the plants if you have never had problems with fungus before. Keep humidity down, circulate air like crazy in the grow space and keep un quarantined outdoor plants out of the indoor space. Don`t wait until after flowering, since it's not a good idea to apply the fungicide directly to flowers. Instead, flowers must be cut off when they are infected. Most fungicides are very nasty, and you won't want to ingest them, so it is necessary to use one that is safe for vegetables. Fungi can wipe your crop quick, so invest in some [SAFE] fungicide and spray down the plants just before flowering if you think fungus may be a problem. Don't spray the plants if you have never had problems with fungus before. Keep humidity down, circulate air like crazy in the grow space and keep un quarantined outdoor plants out of the indoor space. Don`t wait until after flowering, since it's not a good idea to apply the fungicide directly to flowers. Instead, flowers must be cut off when they are infected. Most fungicides are very nasty, and you won't want to ingest them, so it is necessary to use one that is safe for vegetables.
Safer makes a suitable product that is available at most nurseries; it contains only sulfur in solution. Use soap solution like Safer Insecticidal Soap to get rid of most aphid problems. Use some tobacco juice and chili pepper powder added to this for mites. Dr. Bronnars Soap can be used with some dish detergent in a spray bottle if you want to save money. Pyrethrum should only be used in extreme circumstances directly on plants, but can be used in a closet or greenhouse in the corners to get rid of spiders and such. It breaks down within a week to non-toxic elements, and can be washed from a plant with detergent solutions and then clear water. I find Pyrethrum to be the best solution for spider mites, if it is sprayed on young plants up to early flowering. Into later flowering, the tobacco and pepper/soap solution is your best bet, on a daily basis, on the under-sides of all infected leaves. Spider mites are by far the worst offender in my garden. I have finally learned not to bring plants from outside into the indoor space. They are always infected with pests and threaten to infect the entire indoor grow space. It is much more practical to work [WITH] the seasons and regenerate plants outdoors in the Summer, rather than bringing them indoors to regenerate under constant light. Start a plant indoors, take it outside in Spring to flower. Take a harvest or two, feed it nitrogen all Summer and it will regenerate naturally, to be flowered again in the Fall. Once a marijuana plant has been taken outside, leave it outside.
There will be little or no shock if you are quick and tender in your handling of the marijuana plants. Make sure you only need to transplant twice, or better yet, once if possible, through the entire growth cycle. Transplanting slows you down. It takes time, it's tricky, it's hard work, and threatens the plants. Start in as large a container as possible, square is best. 16 ounce | 450 grams plastic cups work OK, and two liter soda bottles cut down may be big enough for the first harvest when growing hydroponically. 1 gallon | 3.5 liter plastic milk or water containers [square] will work too. Or start seeds and rooted cuttings in 16 ounce | 450 grams plastic cups. It's better to have less seedlings than it is to have many seedlings that need constant transplanting. These larger cups take only a little more space, and allow you to transplant only one time before harvesting the first crop. Transplant into a gallon | 3.5 liter water jugs [cut down to 3/4 gallon | 2.5 liter] before forcing flower growth. To regenerate this plant after harvesting, transplant it into a larger pot after it goes into vegetative growth once again, 5 gallon | 20 liter paint buckets work pretty well if you can spare the space, and a 2 to 3 gallon | 7.5 to 10 liter container would make the marijuana plant's second harvest better than the first, given enough vegetative re-growth first.
One more tip:
A Russian study showed that seedlings with at least 4 inch | 10 cm of soil to grow the tap root were more likely to go female. The source I'm quoting says "This may be why some farmers get female to male ratios as great as 80% to 20%."
It's possible to tell the sex of a marijuana plant early, and thus move male marijuana plants out of the main growing area sooner by covering a plant's lower branch for 12 hours a day while it's in a constant light vegetative state. Use a black paper bag or equivalent to allow for air flow while keeping out light. Be sure to set up a regular cycle for these covered branches. If light is allowed to reach them during the dark period, they may not indicate early at all. Use a magnifying glass to look at the early flowers sex type. A male marijuana plant will have a small club [playing card] looking pre-flower with a small stem under it. A female marijuana flower is usually a single or double pistil, white and wispy, emerging from an immature calyx. Some people like to pre-force marijuana plants when they are 8 inches | 20 cm tall, in order to weed out the males. When growing outdoors, many growers do not wish to devote time, space or energy to male plants. Just put the plants on a 12 hours light cycle for two weeks, separate the females from the males, then revert the light cycle back to 18 to 24 hours to continue vegetative growth for the females. Keep in mind, this is a time consuming process and can put the marijuana plants back two weeks in growth. Don't pre-force marijuana plants unless you have lots of time. Just cover one branch per marijuana plant with black paper [light tight, breaths air] 12 hours every day under constant light to force pre-flowers and differentiate early. More about male, female and hermaphrodite plants »
It is possible to harvest marijuana plants and then rejuvenate them vegetatively for a second and even third harvest. A second harvest can be realized in as little as 6 to 8 weeks. Since the marijuana plant's stalk, and roots are already formed, the plant can produce a second, even third harvest of buds in a little more than half the time of the original harvest. When harvesting, take off the top one third of the plant. Leave most healthy fan leaves in the middle of the plant, cutting buds off branches carefully. On the lower one third of the marijuana plant, take off end flowers, but leave several small flowers on each branch. These will be the part of the plant that is regenerated. The more buds you leave on the plant, the faster it will regenerate. Feed the plant some high nitrogen plant food immediately after harvest. When you intend to regenerate a plant, make sure it never gets too starved for nitrogen as it is maturing, or all the sun leaves will fall off, and your plant will not have enough leaves to live after being harvested. Harvested marijuana plants can come inside for rejuvenation under continuous light or are left outside in Summer to rejuvenate in the natural long days.
It will take 7 to 14 days to see signs of new growth when regenerating a plant. As stated before, and in contrast to normal growth patterns, lower branches will be the first to sprout new vegetative growth. Allow the plant to grow a little vegetatively, then take outside again to re flower. Or keep inside for vegetative cuttings. You now have two or three generations of cannabis plants growing, and will need more space outside. But you will now be harvesting twice as often. As often as every thirty days, since you have new clones or seedlings growing, vegetative plants ready to flower, and regenerated plants flowering too. Regenerating indoors can create problems if your plants are infected with pests. It may be best to have a separate area indoors that will not allow your plants to infect the main indoor area. An alternative to regenerating indoors is to regenerate outdoors in the Summer. Just take a harvest in June, then allow the plant to regenerate by leaving some lower buds on the plant, and leaving the middle 1/3rd of the plant's leaves at harvest. Feed it nitrogen, and make sure it gets lots of sun. It will regenerate all Summer and be quite large by Fall, when it will start to flower again naturally.