White Widow
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Temperature and Humidity in the Grow Room
Temperature and humidity are two environmental factors which affect the rate of plant growth, development and yield potential of any crop. Often, in a protected cropping situation, we carefully adjust temperature and supply heating or cooling, but humidity gets overlooked, and it is actually the combination of the two that needs to be taken into consideration.
Temperature
The biochemical functions in plants that are required for growth and survival are `temperature dependant' - that is there is an optimal temperature range within which a particular plant species will be carrying out
photosynthesis at its maximum rate (given that sufficient CO2, water and light are also present). Outside this range, photosynthesis and other plant processes begin to slow down, to the point where they stop and growth ceases. Within a grow room, where control of all plant growth factors - light, temperature, CO2, water and nutrition, is possible, the objective is to provide a temperature range that will maximise plant growth, rather than restrict it. Since different plant species have different ideal temperature ranges, this needs to be matched to the crop being produced. Cool season crops such as lettuce, many herbs and salad greens etc have an optimum temperature range of approx 16 - 22 C. Warmer season crops such as tomatoes, capsicum, cucumbers have a higher range of 18 - 28 C.
Outside these ranges, plant growth slows due to either conditions being to cold and slowing chemical reactions inside plant cells, or becoming to hot, which denatures enzymes and causes cell death. What needs to be taken into consideration when trying to decide on an optimum temperature for plant growth, is the levels of CO2 and light which are being provided. A plant which is in a CO2 enriched atmosphere (1000 - 1500ppm), being supplied with high light levels has a higher temperature optima (at the higher end of the temperature range given) than one which is grown under standard, lower light conditions. For this reason it is possible to `accelerate' plant growth by preventing any environmental factor (CO2 ,light, temperature, water) from becoming the `limiting factor' in plant growth. When high levels of light, CO2 and optimum temperature are provided, the limiting factor in plant growth becomes the speed at which the biochemcial reactions such as photosynthesis can be carried out within the plants tissues -and this is the ideal situation for a grower to achieve, since growth rates will be maximised.
These temperature ranges for 'cool' and 'warm' crops are what should be provided during the 'light' hours right throughout the plant's life cycle. Night temperatures should always be run a few degrees cooler than the 'day temperature' provided for plants and this is usually easier to achieve when heat producing sources such as lights are switched off. There is much scientific evidence to suggest that the growth of most plants is improved when temperatures are higher during the light period than during the dark period.
Temperature Control
In the grow room, lighting is a major source of heat build up, and often removal of excess heat becomes more important than warming the environment. At night however, with the lighting switched off, the environment can cool rapidly, so in order to prevent thermal shock to the plants, heating needs to be run at night to maintain sufficient temperatures in many situations.
There are two types of environment that might be
maintained in a grow room. Firstly there is the closed cycle or closed loop environment, where no air is
introduced from outside. Here, CO2 is replenished
artificially, temperature is controlled via heating or
cooling units, water is removed or added to the air to control humidity levels and the air is thus constantly recycled for use. The second type is where warm humid air is regularly vented outside the grow room, and fresh air introduced on a regular basis. The closed loop system, can be difficult to adequately control and requires the use of more equipment and hence a greater cost. However, in some environments, bringing in fresh air from outside can have major problems where the outside environment is excessively, hot, humid or cold - requiring it to be temperature adjusted before entering the room and well mixed by circulation fans.
Temperature and humidity are two environmental factors which affect the rate of plant growth, development and yield potential of any crop. Often, in a protected cropping situation, we carefully adjust temperature and supply heating or cooling, but humidity gets overlooked, and it is actually the combination of the two that needs to be taken into consideration.
Temperature
The biochemical functions in plants that are required for growth and survival are `temperature dependant' - that is there is an optimal temperature range within which a particular plant species will be carrying out
photosynthesis at its maximum rate (given that sufficient CO2, water and light are also present). Outside this range, photosynthesis and other plant processes begin to slow down, to the point where they stop and growth ceases. Within a grow room, where control of all plant growth factors - light, temperature, CO2, water and nutrition, is possible, the objective is to provide a temperature range that will maximise plant growth, rather than restrict it. Since different plant species have different ideal temperature ranges, this needs to be matched to the crop being produced. Cool season crops such as lettuce, many herbs and salad greens etc have an optimum temperature range of approx 16 - 22 C. Warmer season crops such as tomatoes, capsicum, cucumbers have a higher range of 18 - 28 C.
Outside these ranges, plant growth slows due to either conditions being to cold and slowing chemical reactions inside plant cells, or becoming to hot, which denatures enzymes and causes cell death. What needs to be taken into consideration when trying to decide on an optimum temperature for plant growth, is the levels of CO2 and light which are being provided. A plant which is in a CO2 enriched atmosphere (1000 - 1500ppm), being supplied with high light levels has a higher temperature optima (at the higher end of the temperature range given) than one which is grown under standard, lower light conditions. For this reason it is possible to `accelerate' plant growth by preventing any environmental factor (CO2 ,light, temperature, water) from becoming the `limiting factor' in plant growth. When high levels of light, CO2 and optimum temperature are provided, the limiting factor in plant growth becomes the speed at which the biochemcial reactions such as photosynthesis can be carried out within the plants tissues -and this is the ideal situation for a grower to achieve, since growth rates will be maximised.
These temperature ranges for 'cool' and 'warm' crops are what should be provided during the 'light' hours right throughout the plant's life cycle. Night temperatures should always be run a few degrees cooler than the 'day temperature' provided for plants and this is usually easier to achieve when heat producing sources such as lights are switched off. There is much scientific evidence to suggest that the growth of most plants is improved when temperatures are higher during the light period than during the dark period.
Temperature Control
In the grow room, lighting is a major source of heat build up, and often removal of excess heat becomes more important than warming the environment. At night however, with the lighting switched off, the environment can cool rapidly, so in order to prevent thermal shock to the plants, heating needs to be run at night to maintain sufficient temperatures in many situations.
There are two types of environment that might be
maintained in a grow room. Firstly there is the closed cycle or closed loop environment, where no air is
introduced from outside. Here, CO2 is replenished
artificially, temperature is controlled via heating or
cooling units, water is removed or added to the air to control humidity levels and the air is thus constantly recycled for use. The second type is where warm humid air is regularly vented outside the grow room, and fresh air introduced on a regular basis. The closed loop system, can be difficult to adequately control and requires the use of more equipment and hence a greater cost. However, in some environments, bringing in fresh air from outside can have major problems where the outside environment is excessively, hot, humid or cold - requiring it to be temperature adjusted before entering the room and well mixed by circulation fans.