Temperature & Humidity
HUMIDITY:
Humidity is a very important environmental element that must be controlled for healthy plants, and connoisseur grade meds. Humidity controls the rate of transpiration and how the nutrients are received by the plant. The humidity level is like a pressure cap on the plant, keeping the moisture in the plant, allowing it to have proper transpiration rates of the fluids. Ideal humidity levels in a grow room range between 50% to 70% in vegetative growth, and 50% to 60% for flowering plants.
When humidity levels drop too low, the plants transpire at a rate much quicker than that of nutrient uptake. The nutrients or minerals do not transpire thru the plant, only the water does. So this leaves behind a concentrated level of nutrients in the plant that will actually cause a nutrient burn. Most people don’t realize in situations like these that the humidity could be responsible; usually thinking that it is too many nutrients in the reservoir. Just as a lack of CO2 can cause a plant to go dormant, low humidity can cause a plant to have nutrient problems, resulting from the transpiration rate being much too high in low humidity level environments.
Conversely, when humidity levels get too high, moisture is building up on the plants and walls, forming whole colonies of molds, fungi, and mildews. These pathogens will destroy your garden if not taken care of immediately. This is one more reason why a controlled, closed loop, sealed room is the best way to build and run a grow room, as you can control every element of the environment with the right equipment.
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.
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 maximized.
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.
The closed loop system, can be difficult to adequately control and requires the use of more equipment and hence a greater cost.
One effective way of removing moisture from the air and lowering humidity levels is with a condenser unit – a metal plate which is colder than the surrounding air will cause water to condense on the surface. This removal of water from the air via condensation lowers the humidity.
The interaction of temperature and humidity in the grow room is fairly simple – the warmer the temperature, the more water is lost from the plants. This water from plant transpiration rapidly increases the humidity in the air surrounding the crop to fairly high levels. If this humidity continues to rise and stay at high levels it limits the amount of water that can be lost from plant tissue, slowing photosynthesis encouraging fungal pathogens to take hold and sometimes causing other ‘odd symptoms’. Plant ‘oedema’ is one such symptom which is essentially an accumulation of water in the plant tissue (making it look pale and puffy), this condition indicates that conditions are too humid and warm for plant biochemical processes to be carried out correctly and needs to be avoided. Since plants are so efficient at increasing the humidity of the environment through transpiration, the amount of air change with the outside environment becomes an important factor for crop production. If we look at a similar situation in a greenhouse – where plants are rapidly transpiring, the current recommendation is for 60 air changes per hour to occur with the outside environment. This means the entire volume of the greenhouse is vented out and replaced 60 times per hour – and this is what is required in a mature crop to replenish the CO2, adjust the temperature, and vent out humid air to maintain a good level of plant growth. A grow room has a similar requirement – the lighting adds to the heat load in the small area (where plants are often densely planted), the plants rapidly increase the humidity in the air and CO2 depletion can occur when light levels are high.
Therefore the air in the room needs to be vented out and replaced rapidly. When the plants are small, the plant to air volume is large (there is plenty of air and few plants), and less air replacement is required per unit of time. However by the time the plants are mature and considerably larger, the plant to air volume is small and many more air changes per hour are required to move excess heat/humidty and replenish CO2. This plant to air volume ratio is a vital consideration when a grow rooms ventilation system is designed to ensure sufficient air changes per hour can occur at all stages of crop development.
Air changes are more important during the day – due to the heat build up from lighting equipment, but are also still required at night when humidity levels can still build due to water loss from the plants. Since the environment is often heated at night, some heat will be lost due to having to vent the grow room, but introducing fresh air is important at night since plants require oxygen for respiration and removal of excess humidity.
By keeping a close eye on the appearance of the plants, problems with temperature and humidity soon make themselves obvious Plants that are wilting or have oedema and are pale and ‘puffy’ may be too warm/humid. Dry scorched patches on the leaf tips are an indication of low humidity. As with all other plant growth factors, measurement of temperature and humidity levels in the plant’s environment is the best way to monitoring what is going on in the grow room and allowing the necessary adjustments to be made.
Feel free to chime in with previous experiences keeping your room at these optimal conditions for accelerated growth. I'm all about the accelerated growth. I'll post some more pics in a bit but figured it's going to be a few weeks until the real porn is available might as well chop it up till then.