Ideal Temperature For Marijuana Plants

Ensuring your plants have the perfect temperature is not the easiest thing to do. Some would say it is as much art as it is science.

That doesn’t mean you can’t figure it out, though. You just need to learn a few things first; which I will teach you in this article.

I’ll explain why cannabis temperature involves more than degrees, and why it is even more complicated when growing indoors. I’ll also show you how to recognize temperature related problems and make adjustments in your grow room.

Keep reading to learn everything about temperature while growing marijuana or skip ahead to your favorite section

How does a plant get warm?

A plant’s temperature develops from a combination of external light, external temperature, and the amount of evaporation. A plant’s exact temperature is not something you can read on a thermometer, but it is a definite measure of health.

Marijuana plants won’t usually die from being too hot, but their growth can slow from it. High external temperatures (above 80 degrees) while flowering will not only slow down bud growth but also reduce their smell and potency. If you care about growing buds with plenty of cannabinoids, you need to be sure the external temperature is kept under control during the flowering stage.

The quality of your buds is reason enough to care about temperature, but there are many more.

You also should care about their health.

Be sure to check my free Grow Bible for more tips on controlling your grow environment

In general, too much heat causes plants stress.

If your plant gets too warm, photosynthesis is impacted, enzymes activity decreases, and fewer proteins are produced. Some proteins even break down. If this continues long enough, your plant can die.

Below are some ways temperature impacts the marijuana growing process.

Banana Kush Indoor Seeds

My selection of indoor seeds are perfect for growing in a controlled environment. Although some work fine when grown outside as well, these are the seeds you need if you’re growing indoors.


Most of us understand how plants make sugar right?

Well, one example of how temperature can affect the overall health of your plants is the process of photosynthesis. To a certain degree, photosynthesis is not affected by temperature – it can safely occur at 60ºF (15ºC) or 85ºF (30ºC). Regardless of the temperature, your plant will still be able to produce enough sugar.


Temperature becomes a factor when your plant needs to send those sugars to the places they’re needed. Sugar doesn’t move as well when it’s less than 68ºF (20ºC). In fact, the sugars will get stuck, and your plant will suffer.

In other words, make sure the plant is warm enough to function.

When this happens in mature plants and only lasts a few days, it’s not that big of a problem. Once the temperature is resolved, the backed-up sugars will go where they should be. However, in immature plants, this situation will stunt the plant’s growth.

Not bothered by micromanaging your grow? Grab a Pot for Pot deal and you will be growing your plant in no time!


Another temperature- sensitive function is respiration. Respiration decreases as the temperature drops. This should be a good thing because it lowers the amount of energy a plant uses. However, it also creates a dangerous crutch.

Here’s why that’s a problem:

When a heavier crop develops because of a lowered temperature, total crop respiration increases. Now, when the temperature increases, more energy is needed to keep the plant alive.

That leads to an even bigger problem:

The extra energy requirement leaves little left over for growth.

In my Grow Bible you can learn more about the plant’s biological processes

Heat also causes other problems for cannabis. When it is too hot, your plant is more likely to suffer from:

  • spider mites
  • root rot
  • white powdery milder
  • nutrient burn
  • wilting
  • increased stretching.

These situations are even more likely if it is also humid, or if there is increased water transpiration.

The ideal temperature for marijuana per grow stage

Your marijuana plant will respond to temperature changes differently based on their growing stage.  As a grower, you need to make sure your plants have the best temperature for the growing stage they are in. Below are some ideal temperatures for every stage of the growing process.

Seedlings and clones

Clones do not have their root system yet, so they depend on transpiration for their water. Therefore, they require high amounts of humidity, at least until they have fully formed roots. Many growers use a humidity dome to create an ideal amount of humidity for clones.

Clones like a high humidity
Clones like a high humidity

The ideal temperature for clones is between 68-77°F (20-25°C) with high humidity. At these temperatures, they should quickly form roots and become more self-sufficient. These temperatures are similar for seedlings.

Grow Bible

  • Grow with my Quick Start Guide
  • Discover secrets to Big Yields
  • Avoid common grow mistakes

    Vegetative stage

    During the vegetative stage, young plants prefer a high humidity (70% or more) and temperatures between 68-77°F (20-25°C). However, as the plant gets older, a slightly lower humidity is okay. This is more of an issue for indoor grown plants, as outdoor grown plants are able to withstand more temperature fluctuations.

    The ideal temperature during the vegetative stage is between 68-77°F (20-25°C) with moderate humidity while also providing slightly cooler temperatures during dark periods.

    The cooler ‘night’ periods are perfect for encouraging growth. Don’t let temperatures drop below 59ºF (15ºC). Once the plant matures, it should be able to withstand cooler temperatures during the day and drier air as well.

    I always get strong genetics in my seed store to ensure survivability of the plants

    buy white widow strain

    White Widow has been developed through the years and is a very , very sturdy plant. Learn more about this classic strain.

    Flowering stage

    Once your plant reaches the flowering stage, it can thrive at a comfortable room temperate with low humidity. Unless you are adding additional CO2 to your grow room, a temperature under 82°F (28°C) is ideal. These lower temperatures encourage potent, trichome rich buds that you can smell and enjoy before you burn them.

    Don’t go over 82°F (28°C) because higher temperatures cause terpenes to evaporate and they also slow bud growth. If your buds are too hot during this time, you may be literally burning away the good stuff as they grow, leaving very little taste or smell by the time of harvest.

    Be especially careful to keep it comfortable for your plant after week 6 or 7. This is when terpene production is at its max, and you risk evaporating them due to high heat.

    For optimal trichome production, make sure it is slightly cooler during the dark periods. The change in temperature may trigger increased terpene content as it optimizes plant processes. Just don’t make it too cold.

    This process leads to what is commonly known as the dew point. The dew point occurs when the air can no longer hold any more water vapor, and it condenses into droplets called dew.

    Creat the ideal temperature during flowering stage
    Create the ideal temperature during flowering stage

    If you aren’t familiar with terpenes, they involve much more than taste and smell. They also impact the color of both the buds and the entire plant. Terpenes are responsible for the tomatoes red color, and they possibly may do something similar in certain cannabis strains. With the proper dark-period temperatures, you can bring out interesting colors in your plants (such as blue, pink and purple).

    This phenomenon depends on the strain, of course. Most marijuana plants only grow green buds, but if you want to see what your plant can do, keep it cool for it ‘night’ temperatures and find out.

    Drying and curing

    Harvesting is not the last step to top-quality bud. Even with the best genetics, you’ll need to properly dry and cure your buds. Perhaps half of what determines great marijuana is how it has been dried or cured.

    Professional dried and cured marijuana is more potent, looks better and produces a smoother smoke.

    It will have that ‘sticky-icky’ feeling that marijuana lovers crave.

    Maintain the right temperature and humidity while drying
    Maintain the right temperature and humidity while drying

    If you want the best results from your harvest, focus on maintaining the correct temperature and humidity throughout the entire process. This will help prevent mold and over-drying as well as make it easier to produce the best weed possible.

    One thing people always ask me is when they should harvest their plants. This free Harvesting ebook gives a perfect idea of when to cut your plants.

    Harvest Guide

    • Time your harvest for Perfect Taste
    • Get THC levels for a Perfect High
    • Don’t waste any Precious Bud

      Keep temperatures around 64°F (18°C) and the humidity at 45%. The values in the picture above are not correct. I made these pictures just after harvesting, so temperature and humidity were still high.

      Create a smooth airflow bud don’t blow directly on your buds. This will cause them to dry too quickly.

      Creating the perfect environment

      Whether you are growing indoors or outdoors, you need to be concerned about your plant’s environment. Try and create a temperature that is ideal so that they can thrive.

      Outdoor growing

      With outdoor growing, keeping your plants warm can often be a problem. The good news is that most outdoor varieties can endure temperatures as low as 50°F (10°C) without any problem. That being said, fifty degrees is still not an ideal temperature because it tends to slow down tissue growth and photosynthesis later in the day.

      Anything below 40°F (4°C) can result in damage to the tissue. 

      Results of the wrong temperature

      There are ways to keep your plant warms outdoors. Try:

      • Gas patio heaters
      • Polyethylene plastic covering

      Both options can keep gardens warm on frigid nights. The covering also protects plants from other dangerous weather elements. The idea is to maintain a temperature of at least 60 degrees to promote plant growth.

      Indoor growing

      Indoor growing temperatures are directly controlled by the grower, leaving as much room for error as there is for success. All you must do is make sure your grow room maintains the correct temperature.

      Here’s the problem:

      The ideal temperature in your grow room depends on several factors. The location of your room in the building is an important one for example. A basement grow room is a lot cooler than in an attic with a flat roof.

      Aside from that, the size of your room, the airflow, the number of lights and the extraction rates play an important role. Keep this in mind when building your grow room.

      “Install a maximum / minimum thermometer and hygrometer in all grow rooms.” ~ Jorge Cervantes

      Temperature between 68ºF and 77ºF for cuttings and seedlings
      Temperature between 68ºF and 77ºF for cuttings and seedlings

      When the light is turned on, an ideal temperature for the cuttings and seedlings is between 68ºF and 77ºF (20ºC and 25ºC). As the plants get older, they can evaporate a little bit more, and the temperature may increase to a maximum of 82ºF (28ºC).

      When the lights are off, the temperature should lie between 59ºF and 72ºF (15ºC and 22ºC). Another important rule is that the temperature differences between day and night cannot be too high, a maximum difference of 18ºF (10ºC). So, when it’s 82ºF (28ºC) during the day, it cannot go below 64ºF (18ºF) at night.

      In general, marijuana grown indoors functions best at moderate temperatures between 68 and 77°F (20-25°C) during the light period and a drop of no more than 18°F (10°C) to 60°F (15°C) during the dark period. CO2-enriched plants will produce more at a marginally higher temperature of just under 82°F (28°C).

      If the floor can have a steady temperature at around 80°F (27°C), the roots will be warmed, and the stems and leaves will withstand influxes of colder air. A heating mat is ideal if you’ve only got a few plants to worry about.

      Larger gardens might require the use of a recirculating hot water heater to ensure optimal temperatures.

      Here’s my selection of indoor seeds which all thrive when grown in a controlled environment.

      Bruce Banner is not just a guy that turns into a big green monster… It packs quite the punch as a marijuana strain as well! Be sure to check out Bruce Banner by ILGM!

      Temperature and humidity

      In a grow room, you need to think about humidity as well.

      First, here’s a bit of information on how humidity works. The air our plants ‘breathe’ contains water vapor. The amount of water vapor in the air can vary. This is the humidity.

      In a grow room, the humidity is always a bit higher because the plant’s leaves evaporate water. Marijuana plants only use 10% of the water they absorb for growing and evaporate the other 90%.

      However, the air can only hold a certain amount as well. When this number is reached, condensation begins. You’ll notice condensation as little droplets of water in the colder areas of your grow room or on your plant.

      Temperature plays a huge role in humidity because it affects the amount of water vapor that the air can hold. Warm air can handle much more water vapor than cold air.

      Humidity while growing
      Humidity while growing

      How do you know you are getting close to having too much moisture?

      Here’s what experts do:

      You measure the relative humidity.

      The relative humidity (RH) is a measurement of the percentage of moisture already in the air. For example, an RH reading of 70% indicates that more water vapor can be absorbed into the air. However, 70% at 77 degrees is different than 70% at 68 degrees, because warmer air can hold more moisture.

      Specifically, at the higher temperature, 2 pounds of air could have as much as .45 ounces of water vapor in it. On the other hand, 2 pounds of 68-degree air only holds .32 ounces. So, if you allow the air to cool down, the air can hold less water vapor, leading to condensation while also raising the relative humidity.

      Example: 77 Degree air cooled to 73 degrees – RH rise from 70% to 80%

      This process leads to what is commonly known as the dew point. The dew point occurs when the air can no longer hold any more water vapor, and it condenses into droplets called dew.

      Dew point is important because:

      It helps you find the ideal temperature for your grow room.

      In the example above, we know that the dew point of 77 degrees with 70% RH is 66 degrees. Therefore, we must keep the temperature above 66 degrees to prevent excessive moisture.

      Ideal humidity for marijuana seedlings
      Ideal humidity for marijuana seedlings

      Maintaining proper moisture in your grow room is important because the moisture levels can frequently change.

      A properly ventilated grow room always experiences regular drops in temperature. The heat from the lamps as well as the naturally humid air is regularly sucked out through fans and other ventilation methods, changing the moisture levels.  Even though it regularly changes, you must make sure the humidity levels are optimal for your plants.

      Measuring temperature

      Outdoors it’s easy to measure temperature. Indoors isn’t that difficult either.

      First, you should measure the temperature in your marijuana grow room with a thermometer. There are analog and digital thermometers, and they’re for sale everywhere for a few bucks. I always use a digital thermo/hygrometer (something like this one) with built-in memory so I can see what the maximum and minimum temperature was.

      It’s also a good idea to get one with a temperature sensor on a wire, so you can hang the display outside your grow room, and can see the temperature when the lights are off.

      Measuring temperature and humidity
      Measuring temperature and humidity

      Here are some tips for getting a good temperature reading:

      • Always measure the temperature in the shade
      • Measure at various places in your growing room.
      • Provide good air flow by placing several fans. Lamps emit radiant heat; however, it does not affect the air temperature.

      It will always be a few degrees warmer right under the lamp than in a shaded spot.

      The amount of temperature change that comes from lamps isn’t really an issue; just make sure there’s enough distance between the lamp and the plant.

      Do not misunderstand this, however, as radiant heat does affect the leaf temperature. Therefore, you do not want the lamps to be too close to the plants as this could cause heat stress.

      Grow Bible

      • Grow with my Quick Start Guide
      • Discover secrets to Big Yields
      • Avoid common grow mistakes

        Maintaining correct temperatures

        Maintaining the perfect temperature for your plants can be tricky, but it is not impossible.  When growing indoors, you can control the environment. Outdoor growing is a little less certain.

        Temperature is important for the photosynthesis of your marijuana plants; low temperatures reduce evaporation through the leaves. This causes a suction force, which takes up nutrients via the roots, to become smaller.

        What happens next is:

        The nutrients that are necessary, but aren’t absorbed, remain in the growing medium and eventually disintegrates in the root environment. High acidity in the growing medium reduces the working of the roots which makes the plant absorbs less water and nutrient, and……

        Growth comes to a halt.

        This is why maintaining the correct temperatures is crucial to the health of your plants.

        In a grow room, if the temperature drops below 60°F (15°C) during the dark period, plants will grow more slowly, and yields will not be as abundant. This won’t be readily apparent if you aren’t particularly familiar with the garden’s normal output.

        Grow rooms use lamps, so there’s also the possibility of heat stress.  It is caused by the improper placement of lights. In this situation, the leaves don’t actually burn, but they are damaged.

        This rarely happens to outdoor grown plants because we are referring to temperatures greater than 105 degrees. However, this can occur in indoor setups if you are not paying attention.

        Heatstress on plants - leaves curl up inwards
        Heat stress on plants – leaves curl up inwards

        You’ll recognize heat stress on the top leaves of your plant. They will start to turn yellow and curl inward. This happens as the plant tries to protect itself from the heat. To see it in action, put a lamp too close to your plant. It’s a simple mistake that can quickly cost your plant its life.

        What may seem like a small external imperfection at first, can have serious consequences in an entirely different part of the plant. Therefore, it’s essential to create a good climate in your grow room.

        Correcting temperature problems

        If you’ve already noticed temperature related problems with your plants, it is not too late to save them. Here are three different problems that you may experience in your grow rooms as well as ways to correct them.

        Heat stress

        Prevent heat stress from happening to your plants by keeping your lamps a bit higher than your plants and/or by using a fan to blow away some of that excessive heat.

        If you want something more substantial, try installing air-cooled lights with reflectors that will reduce the heat near the light. Water-cooled lights are actually more effective at diminishing light-generated heat.

        Air-cooled lights, quick fix
        Air-cooled lights, a quick fix

        For the most part, HPS lights should maintain a distance of around 3 to 4 inches per 100 watts from the tops of the plants. Air-cooled lights make the acceptable distance range between 2 and 3 inches per 100 watts.

        Water-cooled lights make the acceptable distance about 2 inches or even less per 100 watts from the plant tops. With light movers, you can move the lights closer or farther away depending on your preference.

        Check this table with distances for all grow lights. Including LED and CFL.

        Temperatures that are too low

        A few nights of cool temperatures won’t significantly damage your crop, but if it continues to occur throughout the flowering period, it can definitely be cause for concern. A CO2 generator or electric heater can heat the room adequately.

        CO2 system setup. Over $1000,- investment
        CO2 system setup. Over $1000,- investment

        When the lights are on, it’s not normally necessary to increase the temperature. The lamps themselves will take care of that. However, it is important to distribute the air over your room evenly so that you’ll get the same temperature everywhere. Use swivel fans for this and aim them between the lamps and the plant.

        Increase the temperature while growing by using swivel fans
        Increase the temperature while growing by using swivel fans

        Fresh air from outside should also be well distributed over the growing area so that there won’t be any cold spots. Especially in winter when the temperature can get below freezing.

        When the lights are off, however, it can get cold in your grow room. Luckily there are plenty of things you can do to increase the temperature.

        Try these options:

        • A simple space heater with a thermostat (keep in mind, they consume a lot of electricity)
        • A radiator with a thermostat
        • A CO2 generator

        You can also turn off the extractor fan (that provides the fresh air) the moment the lamps turn off. This can be done by a so-called fan controller with thermostat, or with a timer.

        These strains are perfect if you have to deal with cooler climates. Both outdoors or during your indoor winter grow these strains are sturdy survivors.

        Temperatures that are too high

        Heat often becomes a problem in a grow room. This has to do with the fact that the lamps produce a lot of heat. Fluorescent lighting is not really a big deal, but HPS lamps can heat up your room to soaring temperatures of 122ºF (50ºC), which is fatal to your marijuana plants.

        How do you not burn up your plants?

        First of all, the dimension of the room is important. For a 600-watt HPS lamp always use a minimum space of 3 ft x 3 ft x 6.5 ft (100cm x 100cm x 200 cm).

        For the extraction, use the following simple formula:

        number of watts divided by two = extractor in cubic feet (meters).

        Using this formula, 2 x 600watt HPS requires an extractor fan of 22000 cubic ft. (600m3). The extractor fan blows the hot air outside and sucks fresh air inside.

        That’s not all you can do, however:

        You can put a carbon filter on your extractor, so it doesn’t blow marijuana smelling air out. You can also put ballasts etc. outside your grow room because they generate a lot of heat.

        Lower your temparature by using a extractor with filter
        Lower your temperature by using an extractor with a filter

        Perhaps the easiest way to keep the temperature low is by running your lights at night. Your lamps will turn on for a few hours after the sun has set and turn off a couple of hours after sunrise. This way you’ll have your lights on at the coolest period of the day.

        You can imagine that if it’s hot weather outside, you’ll also suck this hot air into your grow room with your extractor. So, the room temperature never gets below the hot temperature outside. There are also professional growers who use an air conditioning unit so they can run it during the day and at night.

        Understanding how to provide the best temperature for your plants is one of the easiest ways to ensure a successful grow. You simply need to learn some best practices, measure regularly and adjust as needed. There are plenty of ways to do this, even if you grow outdoors.

        When you focus on providing the perfect temperature, you’ll notice that your plants can thrive.

        Give your plants the best start, however, by purchasing seeds from my marijuana seed store.   We ship to the United States, Australia and a number of other countries. If the order doesn’t get to you or the seeds don’t germinate, then you can get new seeds free of charge.

        Happy growing,


        Frequently asked questions

        Is it a good idea to grow seedlings outside?

        Seedlings require a warm environment and high humidity, typically around 80 degrees. Most outside environments cannot reliably provide these temperatures. For more on seedlings read this article.

        Can LED lights help reduce the heat in a grow room?

        LED lights typically use less energy, but they still produce heat. While you can use them for your grow, keep in mind they may not provide the optimal result. Learn more about LEDs in this article.

        Can marijuana survive with incorrect temperatures?

        The numbers in this article are the ideal temperatures for the best results. Some hearty strains, especially those designed for outdoor growing, can grow under more extreme temperatures

        How does a heat extractor work?

        An extractor removes both warm air and CO2 out of your grow room, helping to lower temperatures on your grow room. Use it with fans and cooled lights to create the optimal environment n your grow room.

        Robert Bergman

        Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations. His passion for growing lead him to develop his own Gold Leaf strain. Now, Robert is dedicated to sharing his knowledge with the world.... [Read full bio]

        GROW BIBLE

        marijuana grow bible
        • Grow With My Quick Start Guide
        • Discover Secrets To Big Yields
        • Avoid Common Grow Mistakes

          56 comments on “Ideal Temperature For Marijuana Plants”

          1. I disagree on the LED lights I have switched from HPS to a good 1000w LED from Mars Hydro and it uses a 10th of the power and same results and yields so far in a grow tent anyway way less heat too Commercial needs may be different but just stay away from the cheap blurpule lights made in China although I think Mars is made in China it may be China’s only good product made.

          2. I use a 4000 watt white rose led lighting system. Bought it on eBay. Light is set to 18 inches above for flowering, then left untouched thru the flowering processs. By the way, I use a 12” pot and miracle grow and they turn out great!

          3. I have a plant in flower a few weeks from harvest and I have a big issue the leaves at top the side of them are curling down the leaves drooping and there turning brown and drying up I recently flushed the plant with clean fresh water and then that night my outside temp dropped in my tent and now I have the issue I just said above please help can’t find wat it could be from online and don’t want to lose this beauty as I’m so close to harvest

          4. So whatever you can I personally you know guide me through A close mouth on get fed right Right

          5. Thank you I read through this article and learned a whole great of stuff I’m a new grower to barely started n have the slightest idea somebody gifted a grow tent to me with all the equipment so I’d figure I give it a shot, build it and start planting I didn’t know it was so much fun but yet so much work So everything is great so far so good now I’m just trying to maintain the right temperatures and humidity inside the grow tent for its in my Room lol Manly I have the HPS 600 W lamp with the air cool system on a five-by-five by 8 tent But my temperature gets up to weigh up to 91 so I open the zipper door and let another fan blow in my apartment air conditioner so it cools it down to about 77 My humility States that it’s about 36% It’s my 1st time the seas are hand-me-downs but it looks like so far so good Before I get into the gorilla glue’s end up white white widow and the Afghan kush all that Goody goodies I want to make sure I know what I’m doing and I got a perfect setup But anyhow your article was very very insightful thank ..

          6. Tom, Thanks for the kind words. Your message was quite broken up but, it appeared you are happy. So..Happy growing in the future 🙂

          7. Jesse, Wheterh or not you plant in partial shade is determined by your climate, and your budget. I recommend you plant in full Sun generally but, it would be advisable to build a rustic frame to support shade cloth over the grow.

          8. My grow partner an I or a 30 p of fru a a 30 pack of y ju see. The seeds showe up in mi 5 da after the or was p. The first cro is a comb of 5 seeds o ea my suprise a pleasure e see sprouted a lived. I soa them f a 20hrs. Then I p the se in a solo cup t spro. I not the f spro ab 40hrs af I p the seeds in the di.and wi in 24hrs t were all spro.thanks f the grea qua. I w l you know h it a tur out in the end.last spr I pur se f canada a I h ab 50% suc ge the seeds t spro. I have 10yrs gr ex.god bl you all at ILGM.

          9. I use led and they do generate heat, just not as much as with hps. The big difference is with the ventilation, HPS requires constant ventilation to keep it cool and you need a heater or air conditioner to control exact temperatures. For led I use a temperature controller on my ventilation so it only turns on when it gets too hot. This is my first grow with led and things have gone well. Just keep in mind the wattage listed on the led lights is mostly bs, I have 4 1000 watt led’s in a 4x4x8 tent, it was too much for veg but perfect for flower, if it was hps or mh 1 1000 watt would be plenty. For led look at the actual consumption not THEIR comparison.

          10. i began with LED and with temp control of the room have gone right off fluros. the three basic rules still apply. 1 temp, 2 air movement, 3 dont over water.

          11. OG Mom,

            Cannabis is adaptable. Just because it can adapt and grow at 100f, does not mean that this is an optimum situation. 😉 Peace

          12. Geroge,

            You definitely do not want seedlings in a 38f environment. They need to be in an 80f + environment with high humidity approx. 70%

            For soil and amending soil information; Go to: where we can help you properly. Great staff and members. Friendly mature forum. See you there! 🙂

          13. If the max for growing cannabis is 85, How come we could grow cannabis in Arizona in the middle of summer when it is more than 100 degrees.

          14. I am really confused about the hot are extraction. You say “For the extraction, use the following simple formula; number of watts divided by two = extractor in cubic feet (meters). So 2 x 600watt HPS is requires an extractor fan of 22000 cubic ft. (600m3). The extractor fan blows the hot air outside, and sucks in fresh air inside.” First you say divide, but then you multiply and non of your numbers make since.

          15. Outdoors it has gotten down to 38f, which I feel may kill seedlings? Also, what about soil type recommendations? We have a lot of sand here and the ph of the soil may be very acidic and need to be made mixed with lots of compost?

          16. nathan,

            35 c or 85 f is deadly to plant cells. The longer a plant is subjected to that extreme temperature the more likely that cell damage will occur. Once a cell dies, it is gone.

            There are several remedies for this type of heat. Perhaps if you join our forum, we can help you find one. Peace, stay cool!

          17. what are the effects on the plant if the temperatures reach but do not exceed 35 degrees centigrade for short periods? (periods not exceeding a few hours?)

          18. It’s a myth LED’s dont generate heat. They do. Enough to keep a room at a good temp. I had to cool my LED down but removing the glass, and turning teh fans around.

          19. What is your take on high DO (dissolved oxygen)? Have you used high DO in the cloning stage? Thanks.

          20. IN the same expanation it is made clear that it is not advisable to allow temps to drop more than 18f. Common sense dictates that this is probably a typo. It is a typo. I went through the article, found your issue, and reported it to the office for editing. Thanks for sharing. Peace, lw

          21. You say “So when it’s 82ºF (28ºC) during the day, it cannot go below 64ºF (18ºF) at night. A temperature difference of 40ºF (5ºC) is ideal.” If its 82ºF and temp drops 40ºF then you are at 42ºF.. Too Cold!

          22. I’m using a 600w led in a 12 sq ft room on at night and cycling off in day keeping the temp between 70 -77 deg the light is full spectrum led working like a charm 7 weeks into the process

          23. You mention a max temp difference of 50F but that can’t be right. You’re converting 10C to Fahrenheit, but since you’re talking about differences in temp, you should use only the slope in the calculation and drop the intercept. So 9/5 * 10C = 18F max difference. I hope this is helpful.

          24. I have used both HP and LED in my grows. I am sticking with LED. My electricity bill is 43% of what it was , I water less frequently and at least in my veg room the results are no less tha phenomenal. As far as product output I get about 10% less but my buds are much tighter due to the lower running temperature of the lights. The PAR and spectrum seem to be better ths the HP lights.

          25. I dont get the fuss about LEDs, frankly, HID produce 130 – 150 lumens per watt, the same as LED and cost TIMES cheaper. So there are no savings on your electricity bill.
            And for the quality of light? Plant needs AMOUNT of photo energy, not the quality, it is not a human eye, its biology and chemistry

          26. […] The temperature should not drop below 64 and not get higher than 86. Around 77 is perfect! The HPS light will produce a lot of heat so if you install it in a 1x1x2m closet without ventilation temperatures will rise up to 125. Use a little more space and temperatures will be fine. All plants should move a little by the air flow in your grow room, just like the wind normally makes plants move. […]

          27. the LUSH brand of lights are the original and best lights on the market. there are a lot of led knockoffs that do not work at all. so be careful

          28. I used the LED flourencents from Walmart with a T8 bulb in the 6100-6300k color range for veg. takes 4-6 weeks to veg rather than 3 bit the flower cycle is roughly the same length so you can veg under LED and flower under good lights and have a constant rotation and save on power. T5 are best but the 2 bulb T8 LED at Walmart works too. I use it and I get great results. my last veg was 2 weeks longer than expected and I ended up with more used space and a yield increase from 24 cured OZ per plant I got nearly 34 cured oz per plant. I have stayed with this system because it works. keep in mine I am using a hybrid hydro system of bubbleponics and RDWC so it can be tricky but the yields are insane especially with the CO2 injection enrichment.

          29. Hi Mike I’m growing ultimate and power plant at the moment one tent has 4 power plant in 25litre air pots 5ft by 5ft and the other same size tent in an eb and flow system at the start we had some heat problems and still an issue at times both have hps 600 watt duel light bulbs have 1000 to 1500 ppm of co2 going in both tents at the start as I said temps went up to 103f which we had to solve by putting lights on at night and leaving tents open we have intake fans on 15 minute intervals and outage on all the time with good air movement in both was thinking after this harvest switching to LEDs as it’s the start of the summer in Scotland and can get hot also the cost is more than expected at £100 gbp per month I managed to keep on top of temp when growing at home but because its elsewhere my friends first grow and he ain’t the freezer space as what I did was freeze 2litre bottles and place behind fan and I managed a great crop would you advise LEDs or a air cooled lamps any advice the hydro grow are drinking 10litres water a day and never drank half that when I’ve been doing in the past here’s hoping my friend can keep on top of temps any advice most helpful like is an ax unit expensive and would this help kind regards T Bear ps was really thinking on going auto what are your thoughts on this and do you have seeds for a hotter climate regards

          30. I’ve not received anything info or any seeds from you guys so please let me know what going on ty . 423-280-0748

          31. Led is by far the way to go! No matter what the energy savings alone are worth it but also the quality of light! If you need proof go to YouTube and put hps v led the results are iutstanding

          32. For Sam & Maria Roberts

            1st we must know what your climate is like in order to determine which lighting setup is right for you. I grow with both. So there are a few factors to look at before deciding which is best for you. As for yields – you can expect the same GPW using either light source… No miracle 2-3 GPW claims here. There are a lot of factors that play into this rather than merely just the light source.

            If you live in the Southern Hemisphere LEDs would be an ideal choice if you do not wish to spend an arm and a leg on AC. Temps from 75-83* are ideal for growing with LEDs. If ambient temps are on average above 90 in summer time. This might be a more ideal cooling or just venting situation vs if you used HID in this climate. Lower temps and your plants won’t be able to perspire, and growth will be slow and may have root rot from roots staying wet too long.

            On the opposite side of things, if you live up North where it can get quite cold, HID would be the choice to go with. Using the HID would supply the heat needed to keep the area warm. ( be sure to block air vents into room! Otherwise this could cause the room to be to warm. Adjust airflow as needed. ) Keeping your canopy at around 72-75 (80 w/Co2 enrichment) is ideal.

            It gets a little cold where I’m at in the winter while it can be quite hot in the summer.. This just takes extra steps to ensure a quality grow. Heaters, AC, running when temps are not extreme.

            But anyways in one area I have 2 8″xxxl w/ 1000 watt Hort. Super HPS. With fans on temps never get above 80* 12″ from light source. So I drop my hood as low as the plants can handle. It’s cold here so I run while the temps are at there lowest, however during the day it’s still pretty cold and even though this has been insulated very well I have to add heat during the day. I also grabbed a few of those mats you stand on while working in the shop to place under the containers as a barrier for the cold concrete floor and the roots.. 4 pack is like $8 at HF. Approx 20″x20″ (heating pad for 2 humidity domes fits nicely as well)

            Last but not least is your overall budget:

            Let’s face it lights can be expensive, not to mention everything else that is needed. You can spend over $2000 easy on one LED light fixture… Crazy! While you can find cheaper ones… Get one that has proven results, cheap imitations can leave you feeling frustrated with poor results.
            HIDs are much cheaper, and they have worked great for over 20 years. While they have had advancements and become cheaper in recent years. As for brands there are so many… If budget isn’t a problem then get what ever you fancy.. Some have high end looks too if that’s your thing…
            But if your just looking for something to get the job done and well too, you can pick up a 1000 watt switchable digital ballast, Horti. Super HPS bulb and 8″xxxl hood for right @ $400 with free shipping.

            For more direct response you can find me on FaceBook under the same name.
            Hope this helps!


          33. This is all a matter of choice. Without knowing what size grow you are considering I can only offer my opinion.

            LED is expensive compared to HID. The newest digital hps/mh switchable, adjustable power output all in one systems are not that hot. In fact; When set up with proper ventilation, you will enjoy the warmth.

            If you are worried about electrical consumption; Your yield is always going to suffer. I use a portable AC unit with dehumidifier built in. You cannot merely use LED lamp as a cure all for heat, humidity or electric consumption.

          34. We are getting ready to start growing… we’ve been doing a lot of research on lighting. We’re wondering why or if LED lights are even a possibility for growing? They have an abundant amount of lighting without all the heat plus they use very low wattage compared to other lights… is this something that would work or do we need to use another type of light for the heat element as well? What do you think/
            Completely confused,
            Sam and Maria

          35. […] The flip side is making sure that your grow room doesn’t get too hot. If the temperatures are too hot, the plants can be damaged. You might experience weak stalks and stems, as well as wilting droopy plants. Consider your ventilation in too-hot grow rooms, and possibly adding an air conditioner if you’ve already run out of other options in how to adjust the ventilation in your plant’s environment. Read more about the ideal temperature for marijuana plants. […]

          36. OK just a quick question… My girl isn’t growing very much and is only 13 inches IF THAT at 42 days of vegging. She was badly burnt by I guess getting hold of a TR nute ball in the soil and was horrible looking she bounced back quickly nicely and super fast at least a node a day and a half. Now it’s like a node for every 2 days or even three. I don’t have much for her heat wise and sorta wondering if I should get a heating pad for her. My house runs cold natrually but I’ve been able to manage 75 to 82 degrees Fahrenheit since germination. Hope to hear back soon and the article was great to read I even wrote some things down too lol thanks again