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Cultural Healing and Life

The Indoor Garden Environment - Part 2 - Temperature

JJ the Gardener

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The Indoor Garden Environment

~A Cultural Healing and Life Compilation and Writing.




Temperature & Gardening

To be wise in regards to temperature in gardening is to appreciate that temperature affects two main aspects in the garden.  The environment and the plant.  In gaining an appreciation of these two perspectives and their cumulative and lasting effects is the beginning of taking control of your garden environment rather than your gardens environment controlling you. 

Once we understand this concept we can discuss how to control the environment to our advantage to limiting adverse uncontrollable situations like heat waves or periods of high or low humidity. 


The below formula is made to help illustrate this aspect.  

Temperature/humidity effects on environment + Plant physiology/effects = Temperature in gardening knowledge



Temperature perspective in regard to the garden environment

The first perspective of temperature is the environment perspective as temperature is the guiding factor that directly determines the effects, positive and/or negative for all other environment factors in your garden.

  • Such as raising or lowering temperature can affect the humidity and the effect on the plant itself ranges from comfort level to affecting its daily biological functions (leaf to root pressure) to negatively impacting the plants development stage. 
  • Further still, temporary bad temperatures that cause stress can have reactions that enable a setting favorable for mold pathogens and other similar negative effects on the plant. 
    • If a plant is not healthy (nutritional) and fit (Brix levels) during stress times plants can become more attractive to pests and disease causing further problems.  :cute-little-worm-hi-and-bye-smiley-emoticon:

Understanding temperature and its effects on your environment and that upon your plants physiology and development will enable the gardener to transform temperature as a feared grow barrier to a hard to control force to being just another tool in the gardeners tool box and a simple factor to account for.


Garden Temperature Effect Formula:

Temperature & Environment (humidity) from canopy/middle/low fruit/media/root media level


_____Plant Physiology & Plant Development + Impact over time_____

= Garden Temperature Effect.



Genetic & Climate Tolerance

Plant type/strain/phenotype @ Climate Tolerance + Match Environment = Good plant Genetic

The Second perspective to temperature is from the plants perspective.  We tend to take the plant for granted that it will just automatically respond wonderfully to our specially designed environment.  However, before we can go that far with our expectations we need to ensure that we have the correct genetics, phenotype and sensitivity aspects accounted for that matches the garden environment or the garden environment adapted for. 

  • Hot and dry areas you want plants adapted for that climate.
  • Humid and hot areas you want plants adapted for that climate.
  • Account for known sensitivities or discard that genetic in favor of those who better adapt.

Regarding the type of plant environment think and research about the time of the season and how the plant would naturally and traditionally be grown.  We just want to match those conditions as best we can for the type of plant and the strain and phenotype. 

  • For example, spring environment for natural seedlings, early growth, pre fruit/flower, transition period, early flower, middle flower and end of flower/fruiting environments. 

The next part is to understand how temperature and relative humidity affects the plant.  By understanding this aspect you can gain the knowledge to control your environment as necessary and to optimum conditions if so desired.


Good video on temperature and other factors.


Everest Fernandez

Temperature, Humidity, Light Intensity, Spectrum and Plant Physiology

The key to optimizing lights in the environment is to control the heat.  We want to find the sweet spot that maximizes a lights intensity, spectrum and penetration with favorable conditions at all viable plant depths.  Either using one or multiple lights each light is treated the same way to determine optimum settings in terms of cooling and heating.


Light intensity & Environmental Formula

Temperature and humidity @ various plant levels + plants physiology = light intensity/quality


Often, If canopy temperatures are too high gardeners will often increase the distance between the plants and lights.  This directly affects light intensity and spectrum at depth due to light loss with increased bulb to plant distance. 

  • Air conditioning options.
  • Air cooled reflectors are options.
  • CO2 use.

This directly impacts the quality and yield of the plants lower fruits if lights are moved out the optimized distance.

  • Take light intensity into consideration no matter how close you are able to get light to your plants with cooling if you are able to get to close to a plant due to effective heat control. (light bleaching.)
    • Palm test - if too hot for your palm after a minute it is probably to hot.
    • Lumens -  
      • 50,000 to 20,000 lux is acceptable.


Temperature and humidity effects and damage can range from:

  • Reduced photosynthesis.
    • Leaf damage
      • Heat damage
        • High humidity shuts down plant process
          • negatively affects transpiration and stomata function.
        • Low humidity affects
          • Too dry air negatively affects transpiration rates
            • increased intake of water and nutrients
            • can lead to nutrient burn and other nutritional aspects
      • Light bleaching if too close
    • Lower light spectrum aspect if canopy is not maintained at good environment temperature/humidity.
      • Adjust light distance if applicable.
  • Media environment stress will alter the bio life of your media to potentially negative aspects.
  • Intersex plant trait potential due to stress depending on plant sensitivity and type.
  • Temperature and humidity can alter the media and the plants uptake and intensity levels of nutrients to dangerous levels.
    • This can affect temporary situations such as lock outs.
    • Can create longer term effects such as adding to soil/media acidification and creating a domino effects from causing locks to inviting

To visualize these effects in human comparisons think of a baby to teenager (seedling/cutting to veg) and/or an adult to elderly person (mid flower to harvest time frame) in harsh environments be it hot or cold this effect is dramatic on the younger people and older people (kids in cars and elderly people without air conditioning or heating as example) just as it does with young, elderly and sensitive people it is the same with most plants. 

  • This is why predators in the wild like old, the sick, the injured and the babies of their prey.  Easier meal as they are weaker.

This aspect is rarely appreciated by those who believe they understand temperature.  If you are after quality and yields, pay very close attention to your temperature levels doing your very best to not go into stress situations.  Just like "Goldilocks", plants like it just right.  Not to hot and not to cold.

  • You are also prepared to understanding on when to induce stress as applicable for your plant type. Be it to induce fruiting, sweetness or any pertinent factor for the plant being grown.
  • Some plants require stress factors to help them enter their next development stages.
    • Stable all the time is not necessarily as a good as matching the plant environment with its developmental stages.

Things to help manage stress:

  • When outdoors, encourage deeper root growth.
  • B-Vitamins before, during and after
  • High brix
  • CO2 use (PPM dependent)
  • Air conditioning
  • increased air flow/breeze above and through the plant.
  • If dry heat add some humidity depending on your plants needs at their development stage.
  • if humid head reduce humidity depending on your plants needs at their development stage.
  • Ensure reservoir water and watering in water is at a correct temperature.
    • Add ice bottles.
    • water chill system.
    • increase aeration when water temps rise.
      • lower oxygen content in warmer water.
      • low oxygen and warm water is good environment for root pathogens.
    • Add H2o2 to water periodically and 5 minutes before feeding to increase oxygen to water levels.
      • H202 breaks down into oxygen.
  • Ensure media temperature does not get out of proper range.
    • Smaller containers may be transplanted depending on stage of development of plants.
    • Larger containers soils should be shaded (if not already by plant).



Union Break!


I think this is how some might feel!



Garden Temperature Planning

During the planning stages of a garden the plan will often take into consideration the intensity, spectrum and over all the strength of a grow light in terms of yield and quality and work from the top down depending on what they can afford to purchase.  Generally people think they will be automatically able to place the light at optimum levels as stated in marketing for light quality, penetration and per suggested light distance from the plants but they do not appreciate their ambient and the entirety of the operating temperatures and the lights impact on temperature.

No matter what marketing says your garden temperatures will be determined along with other factors such as natural ambient temperatures and humidity and this directly affects the efficiency and overall quality of your lights in terms of heat, light intensity and spectrum in regards to the light penetration of the plants. 

Otherwise the scenario where gardeners purchase a high wattage light and cannot control the heat.  A very common situation that leads to the gardener raising their costs by adding in cooling options to make the situation more palatable to the plant.  The best answer is a reduced wattage light that equals the best operating temperature.

  • Having a 600w HPS or a 1000w HPS so high from the canopy due to heat that it is essentially a 400w light is not efficient use but this is fairly common, especially during summer months where budgets do not include effective additional cooling options.

Some people will consider LED lighting or other low temperature lighting in comparison to HPS or other high heat lighting and this is a valid option but I also recommend reviewing a smaller wattage light and in combination with another light for a better light spectrum. 

Which ever will give you better spectrum with good penetration taking into consideration the operational temperature of your garden. 

  • This is rarely the big light choice when the high wattage lights impact upon the garden is appreciated after taking into consideration impact the light brings to the operational garden heat as a whole and with other costs associated which typically lowers the lights efficiency in comparison to the other options. 

To plan out a garden environment we need to consider all the elements that make up the garden environment and affect temperature specifically.  Such as mechanical equipment and the natural ambient temperature so that we can determine cooling and/or heating requirements. 



How To Determine Heating and Cooling for Environment

Natural Ambient Area Temperatures - This is the normal temperature of the area you are going to grow in prior to starting.  We will use this in estimating operational temperature.

  • Day and night temperature at high and low temperature and humidity readings.
  • This information will determine if we need to add cooling or heating just to prepare or set the garden environment.
    • We will use this as our Natural Ambient Temperature


Natural Ambient Temperature Formula

Natural Ambient Temperatures (day and night) for operating seasons (intake air).


_____Estimated Heat (Lamps, fans, CO2 burners, insulation etc) @ BTU and/or Watts____

= Estimated Operational Temperatures per season as applicable

@ BTU and/or Watts for cooling and heating requirements



Now to determine the "Operational Garden Temperature" and then we can make adjustments to the build plan to obtain our environmental goals during the planning stages.


Operational  Temperatures: 

Intake temperature (outside/lung room air) needs @ BTU and/or Watts for HVAC


_____Grow room heat (Lights + other)_@ BTU and/or Watts for HVAC

= Operational Garden Temperature HVAC requirements

(Day and night highest and lowest temperatures per day for each change in intake air such as each season).




By adjusting the BTU/Watt requirements for the selected lights it can be estimated to an acceptable range of accuracy the impact that each light will have on the cooling or heating requirements for the garden.  As a general rule if the numbers are close I recommend going the light size lower or increase the BTU/watt requirements for additional cooling as to ensure better optimization for light penetration and spectrum.

Further additional BTU/Watt, cooling/heating consideration for:

  • Insulation properties of the room, ducting and any other pertinent factor.
  • Air conditioning, dehumidifiers, CO2 burners and ventilation are also factors to consider.
  • Add the wattage of heat generating aspects with the type of insulation and we can determine the cooling or heating requirements.



Grow tent 3x3x6 in a basement area that is consistent at 65℉= 18.3℃.  Should a 400w light require cooling.

  • We want to determine the cooling required for a 400watt HPS for a 3x3x6 size tent. 
    1. http://www.eyehortilux.com/education-room/btu-calculator.aspx
      • Enter 400w light wattage = 1365.200 BTU/HR
    2. http://www.calculator.net/btu-calculator.html
    3. Once the BTU needs match that of your light and combined needs of your room.
    4. Add the degrees needed to cool the light from your desired garden temperature.
    5. This is the temperature that can be estimated by your lights.
      • This will determine if cooling or heating or nothing is appropriate.
        • In this examples of a 400w HPS in a 3x3x6 tent with stable ambient temperature at 65f.
          • You will need 1,360 BTU/hour or 398 watt to cool this light by 20f to reach desired setting.
          • http://www.eyehortilux.com/education-room/btu-calculator.aspx
          • Since it will take similar BTU/watt requirements to cool that matches our light BTU/watt requirements at 20f we can determine the light will add approximately 20-25 degrees of heat to our ambient temperature.
          • Total heat is estimated to be in the 80℉= 26.6℃ to 85℉= 29.44444℃.
            • A  bit on the upper high side of acceptable.
            • Add air conditioning for better environment and less risk.
            • Add air cooled reflector.
            • Reduce to next light wattage option down/dimmer switch on light.
            • CO2 considerations due to plant temperature benefits if run on high side but may be more cost effective to consider cooling options.

Once all the BTU/wattage requirements are known and accounted for at depth of the plant for light intensity you can determine the entire cooling or heating needs by simply working your overall BTU/watt requirements as you did each light.  This will give you a good estimate on realistic garden environment and its requirements. 



Temperature in the Garden Summary

Once a gardener understands to an appreciation the perspectives and effects of temperature and how to control it the gardener can utilizes this knowledge to manage their crops effectively and expertly to the degree of control they build into their garden systems.



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