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    Thread: Growing Environment

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      Default A Growing Environment: atmospheric thoughts

      Taken from "The Growing Environment" originally published Jan/Feb 2001
      from the magazine "Maximum Yield"
      by Erik Biksa


      Inline, centrifugal fans and shaded pole blowers (squirrel cage fans) are best suited for indoor applications.....Axial fans, muffin fans, duct booster fans. etc. are not well suited to exhausting grow rooms. However, they can be used to exhaust smaller grow chambers, cabinets, etc, providing adequate air intake opening where fans are also supplied. Axial fans and muffin fans are wonderful for spot cooling HID lighting or used in conjunction with air-cooled lamp shades.

      Air for intake to the grow room is best drawn in from outside if no central air conditioning or heat exchanger is available. Ideally, all intake air should pass through an activated charcoal filter to remove spores, insects, etc. Keep in mind that any mend or item such as filters in the ducting will restrict airflow, thereby increasing fan capacity requirements. Usually, a fan of equal or greater capacity to the exhaust fan is required to deliver air so that exhaust output is not restricted. This is the ideal situation. However, by using an exhaust fan with higher output than required, the intake fan need not be as large because static pressure has been accounted for.

      Ventilation requirements can be reduced with modifications to the growing environment such as air-cooled and water-cooled lights. In this regard, most of the heat generated by the HID lighting doesn't make its way into the grow room as it is directly removed versus being removed from the grow room as it is being dissapated. They also reduce "hotspots" in the grow room, allow for the plant to tolerate a closer light source and provide more efficient use of CO2 enrichment, all of which will increase yield.

      The exhaust cycle can be determined by use of timers (mechanical or digital), cooling thermostats and de-humidistats. Some growers have their fans wired to all three. Somebody with a little experience can integrate the three via relays. Commercially manufactured units are also available. For example, calculations have determined that the CO2 burner needs to be on for 15 minutes every hour to supply 1500 ppm of supplemental CO2 in the growing area. We don't want to run that all at once, but disperse the amount more gradually over a period of one hour. When the lighs are on, the CO2 timer is on, so once every 20 minutes the generator cycles for 5 minutes, providing for 15 minutes of combustion every hour.

      The cooling thermostat is set at 80 degrees, and the de-humidistat is at 60%. If during the one-hour period conditions rise above these set points, the fan will cycle until they fall below. If neither of these set points are exceeded during the one hour period, a cycle timer will turn the exhaust and intake fan on for five minutes every hour. This type of control is difficult to attain without using central air conditioning or heat exchangers.

      Air-cooled lighting is just shy of necessity with this type of set-up. Often the temperature rises rapidly due to the HID lighting and is further increased from the CO2 burners, activating the exhaust fan and intake while the CO2 burner is on. If the price of propane or natural gas is not an issue, your plants will still benefit from some of the additional CO2 flowing over the surfaces of the leaves as the air is exhausted.

      Commercially manufactured units and advanced "hydro-electricians" can allow the cooling settings to override the CO2 burner, keeping it off anytime the air is being exchanged.
      If you are able to successfully achieve this level of control in the growing environment, you will be able to use temperature to manipulate plant responses to the growing environment to your favour. To keep shorter plants with tighter internodal spacing you can experiment with maintaining warmer night temperatures than day temperatures during vegetative growth and up to the first two weeks of flowering. Having warmer temperatures during the day and cooler nights is most common with indoor grow rooms. This increases cell elongation for more loosely branched plants with larger internode spacing. Some varieties are more sensitive than others, and cooler nights can bring on early flowering, even with longer days. By maintaining the room 20 degrees cooler during dark cycles for the last two weeks of flowering, you can help to speed up ripening. Take care, as humidity will also increase with a sharp drop in night temperatures, which cn lead to blights and mildew on densely packed flowers. Plants that are still actively growing, or when cut for processing will convert stored starch to sugar in warmer temperatures, and convert stored sugar to starch in cooler temperatures. This type of growth manipulation has been coined "D.I.F," as the differential in day and night temperature is the factor that is influencing plant characteristics.

      Humidity can also play a role in managing plant growth. Growers know that unrooted cuttings require high levels of humidity to prevent dehydration. Plants absorb water through their roots. The water then travels through the plant through tiny vein-like structures called xylem, and then travels through the leaves and exits as a vapour through tiny pore-like structures on the leaves called stomata. Stomata are also used for CO2 assimilation. The rate of water intake through the roots versus release rate through the stomata determines turgor pressure in the plant. This is what gives a plant its rigidity. If the plant has no roots, the humidity around the plant must be higher so that water uptake requirements are low due to reduced evapo-transpiration rates. In more mature, actively growing plants, lowered humidity will result in an increased uptake of water and nutrients. This rate is further increased with CO2 enrichment. For un-rooted cuttings, humidity levels of 85-95% are optimal. Different plants will prefer different levels.....

      Carbon makes up the majority of a plant's dry weight. It is absorbed from CO2 gas in the atmosphere through tiny openings in the leaves called stomata. Carbon Dioxide is as essential to plant growth as the oxygen we breathe is to us. Many plants will benefit from raised levels of CO2 in the grow room. It is especially beneficial for rooted cuttings and vegetative growth. Some growers use CO2 enrichment throughout all stages of plant growth. Carbon Dioxide can impede maturation in ripening plants, and can result in diminished production of terpenes (what gives the plant its flavour and scent) and can decrease the production of other essential oils as well. Typically fresh air has about 350 ppm (parts per million) of CO2 in the air. Increased levels from 1000-3000 ppm will generally increase yields by 20-30% and take a couple of weeks off a three month growing cycle. For smaller areas bottled CO2 is best. In fact, if it were economical, bottled CO2 is the best choice even for larger areas. Bottled CO2 will sink fast to the floor when released. It must be circulated through the plant canopy via carefully positioned oscillating fans to keep it from sinking or exiting the growroom....

      Most plants benefit from CO2 only during the light cycle. Orchids are an exception. The least expensive way to control CO2 is through the use of timers. A "COMPUGAS" device is available from some hydroponic suppliers. The grower simply types in the dimensions of the grow room and plugs in the solenoid from the flow meter and fans into the unit. Otherwise you have to make some calculations of your own.

      In a 10 x 10 x 10 foot area there is 1000 cubic feet. One cubic foot of CO2 in this room should provide an additional 1000 ppm of carbon dioxide. Two additional feet would supply 2000 ppm, and so on. If you wanted an additional 2000 ppm and you set the flow meter to 20 cubic feet per hour, the tank would have to run for six minutes every hour. It would be best to release it four times for one and a half minutes every hour. An Intermatic C8865 one hour cycle timer can be plugged in only to run when the lights are on. It can be wired so that when the exhaust and intake fans and CO2 regulators are plugged in the fans will run on the "off" period for the tank, and will shuf-off while the CO2 is activated, all running on the same timer. The wiring for this situation might take some practice however.....

      Carbon Dioxide gas can also be used to preserve dried flowers if the gas is released into mason jars before tightly closing the containers loosely packed with the product. Carbon dioxide enrichment should only be supplied when all other conditions are optimal. The plants will only grow as fast as their most limiting factor allows, so if oxygen levels at the roots are low, for example, the plants can only grow as fast as the amount of oxygen that is made available to the roots. In contrast, however, many greenhouse growers will add carbon dioxide in winter months when light and temperature levels are lower and find that it increases production.

      The above are just a few tips that will help you to achieve better results by better managing the growing environment for growth manipulation. This is a valuable technique that is often overlooked due to growers focusing primarily on other growth factors such as light and nutrients. It is also important to remember that if all factors are optimal and managed accordingly, the plant variety itself becomes the limitation.
      Last edited by Rellikbuzz; 4th April 2006 at 04:43 PM.

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