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Heat stress is most common for indoor plants. Growing marijuana indoors is the most effective at a temperature of between 70 and 75 degrees Fahrenheit during the plants’ period of light, and somewhere between 50 and 60 degrees Fahrenheit during their period of darkness.

If your plants are enriched with carbon dioxide, they will function better with a higher temperature, somewhere just below 80 degrees Fahrenheit. Learn everything you need to know about heat stress.

What is heat stress

Cannabis heat stress

You will find that you plants have a heat problem when the temperature is below 60 degrees Fahrenheit. If your crop has just a few cool nights in a row, there shouldn’t be a strong effect. If, however, there is a cool period that lasts through the flowering phase, you will not be happy with the results.

Your plants require the right amounts of heat everywhere, including from the floor. If the floor remains at a constant temperature of around 80 degrees Fahrenheit, your plants’ rooms will be cozy and warm, and your plant’s leaves will be able to handle random moments of cold.

Download my free marijuana grow guide at this link for more about heat stress

Because marijuana is a hardy plant, outdoor strains are generally able to handle temperatures of as low as 50 degrees Fahrenheit, without there being any lasting effects. Although they can handle this temperature, it doesn’t mean it is ideal. Growth and photosynthesis will be slower than at warmer temperatures. If the temperature drops below 40 degrees Fahrenheit, there will be lasting tissue damage.

If your plant is too hot, however, the problems can change substantially. As long as your plants have established large root systems, they should be able to survive major heat fluctuations. This is simply because plants with bigger root systems can absorb higher amounts of water. When your plants are in their vegetative stage of growth, elongated stems can be a result of temperatures between the 80s and 90s. If your plants are flowering, the buds could turn out to be airy.

Signs of heat stress

Signs of cannabis heat stress

Plants that are experiencing temperatures that are too low will have slowed growth and smaller yields. These signs can be difficult to spot if you aren’t completely familiar with your plants’ regular output.

You will know your plant is experiencing too much heat because the buds closest to the lights in your grow room will look stretched and bleached, or because the tips of your plant are burnt. The bud problem is a sure way of distinguishing the problem as heat rather than too much light.

Your plants that are undergoing heat stress will also start showing signs of stress through yellowing and brown spots appearing. If you haven’t been watering your plant enough lately, it is more likely to experience heat stress.

How to fix heat stress problems

How to fix cannabis heat stress

If you are growing outdoors, try using a gas patio heater to keep your garden warm through the night. Your idea temperature is a consistent 60 degrees. This will allow the plants to grow optimally. Another way of keeping heat from escaping your garden is by covering all your plants with a polyethylene plastic covering. If you are having a serious cold problem, you can even add a heater to your outdoor setup.

If your grow room is too cold, try equipping it with a CO2 generator or an electric heater. If you have a larger garden, you can keep the floor nice and warm by using a recirculating hot water heater.

If you are growing your plants indoors, try using ventilation (have a fan blowing over the tops of your plants) and air conditioning, or water or air-cooled lights to lower the grow room temperature. You won’t need to worry about the temperature between the plants, but rather the temperature that is directly hitting your plants, instead.

Download my free marijuana grow guide at this link for more about heat stress

If you have an outdoor garden and excessive heat is the issue, you can use micro-sprayers to lower your plants’ temperatures by between 20 and 30 degrees Fahrenheit. If your plants are being grown in containers of come sort, you will need to be extra cautious when it comes to temperature. These plants can easily overheat. If they are root-bound, transplant them to a larger container that is light-colored and, therefore, will reflect light instead of absorbing it. You can also simply move these plants to a location that is out of the direct sunlight.

For your outdoor plants, try watering them in early morning or evening times so that the water doesn’t evaporate right away. You can increase shade by putting a covering over your plants, such as an old sheet. Make sure not to cover them for too long, however, as it will cause their reintroduction into the sun to be a serious shock from the sudden increase in light intensity.

If your indoor plants are experiencing heat stress because they are too close to the lights, then you can simply move the lights away from the plants. This is the easy way to solve the situation at first, but for longer-term benefits more serious techniques may be necessary. For instant results, air-cooled lights that have been equipped with reflectors can lower the amount of heat that comes with the light. Water-cooled lights do the same thing but are actually more effective than air-cooled lights.

Your loon-watt lights should always be around three feet away from the top of your plant. This changes when you have air-cooled lights, which are fine if they are between 18 and 24 inches from the tops. Water-cooled lights can be even closer, ranging from twelve inches to even shorter distances.

You can also vent out the heat from your grow room by using an exhaust system, or fan. You can combine it with a carbon scrubber to remove any smells that might otherwise be propelled outwards.

If your plants are in their recovery phase of dealing with heat stress, you can try using seaweed kelp extract to assist in the recovery process. It also will have the added benefit of avoiding future heat stress from getting your plants.

Marijuana plant symptoms

Cannabis symptoms heat stressLeaf edges burnt or browning
Upper leaves/newer growth affected
Leaf edges curling upwards
Wilting and drooping of leaves
Wilting and drooping of entire plant

Your plant’s tendency to experience heat stroke can also depend on its strain. Indica strains, for example, are most likely to get their heat stroke when they’re undergoing their flowering stage.

Thanks for reading. Please leave comments or questions below and don’t forget to download my free grow bible

Robert

21 Comments

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  1. By Robert

    ,30 Jul 2015
    Thanx people……being older my mind forgets things and especially after the chemo I received back in the spring. I do have the grow bible and I will refer to it……..also thanx for the response on my question on germination…. RKM
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    1. By lee

      ,03 Sep 2017
      Hi . My auto weed plants have all the same problem were can I sent you email with some pictures for help pls
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      1. By Roy ILGM

        ,04 Sep 2017
        Hi Lee, the best place to get grow support os on the support forum. Our experts will be with you shortly.
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  2. By Flintz

    ,30 Jul 2015
    ILGM, I’m building a new grow closet in my office and temperature is a concern, I can’t put ventilation holds in the wall on any side, so I’m gonna need a cool light that will give me good yields, any […]Read More
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    1. By Chris

      ,07 Oct 2016
      CFLS are the coolest light you can get and they do and can produce nice yields
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  3. By Robert Walch

    ,31 Jul 2015
    So many typo’s. Do you edit your articles prior to publishing.
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    1. By latewood

      ,31 Jul 2015
      Well; I make typos because, I am legally blind. You are welcome for all the free information.
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    2. By GreenGrannie

      ,10 Aug 2015
      Just be grateful for the information! ~Peace
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  4. By latewood

    ,31 Jul 2015
    Flintz, Although you can set up a grow that way; You won’t be able to achieve good yields without proper lighting and environment. If you can leave the Office door to closet open so it can receive fresh cool air, […]Read More
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  5. By Danny

    ,01 Aug 2015
    my plants are outside in pots they are yellowing leafs and broen tips on afew of the leafs its been 80 and 90 these past couple mths what can I do to save my plants
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    1. By aj

      ,21 Sep 2017
      Get them indoors when its over 75 outside, google mj too much heat, give you all the answers
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  6. By Minei Kiefer

    ,03 Aug 2015
    Aloha, Well summer is my biggest grow of the year but the most brutal grow. It is always so hot from May thru August. It just seems to vet hotter every summer. Here in Hawaii, there is no options of […]Read More
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  7. By Minei Kiefer

    ,03 Aug 2015
    Sorry for typos.
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  8. By latewood

    ,05 Aug 2015
    Hi Danny, Without more information; It would be hard for me to guess. I can advise you to join our Support forum, and fill out a “Support Ticket”. This will allow us to read more baout what you are doing, […]Read More
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  9. By latewood

    ,05 Aug 2015
    Hi Minei Kiefer All I can suggest to you is to invest in some 50-60% shade cloth. Build a little lean-to, or make a frame and cover it with the shade cloth. I am sorry to say; There is no […]Read More
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  10. By Sunmork

    ,06 Aug 2015
    Hi Robe Great information you give all of us that wants to grow nice plants ourselves :-). I have a question to you though. Would you be able to arrange your info sites so as we can print them on […]Read More
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    1. By latewood

      ,10 Aug 2015
      Sunmork , Have you downloaded the Free Grow bible? It is in PDF format, and is printable. 🙂
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  11. By wombat

    ,07 Aug 2015
    Hello I made the rookie mistake of having my nursery tent in the same room as my grow tent so my new plants from seed were exposed to very low temps so looking very sick very purple stems with yellow […]Read More
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  12. By latewood

    ,10 Aug 2015
    wombat, IN order to really help you; I suggest you join our support forum where we have many expert growers to help you grow successfully. 1st thing to do when you join is to start a topic with a “Support” […]Read More
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  13. By jean cocteau

    ,20 Jun 2016
    hello everybody i’m growing 2 autoflowering outdoors and for work reasons i left out of water for 1.5 day. The biggest plant (55days old) has already a big sort amount of uncreated buds…but the day i left unwatered summer heat […]Read More
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  14. By adam

    ,29 Sep 2017
    really helpful, thank you for this
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