Climate problems & your marijuana plants

Whether it’s excessive humidity or a temperature that’s too high, climate fluctuations can have a strong effect on your marijuana plants.

Growing areas have a natural tendency to be high in humidity since moisture is let off from marijuana plants.

A grow room that is too hot will also lead to issues. Take action to ensure that your plants don’t experience long-term, negative effects.

Signs of a climate problem

You will know you have a temperature problem when your marijuana plants begin showing signs of stress, specifically on the leaves nearest the source of light (or heat if it’s a different source).

If you want to know what the best light schedule for your marijuana plants are, read our comprehensive guide.

These leaves will begin to yellow, and brown spots or burns will start popping up.

Download my free marijuana grow guide and start growing healthy marijuana plants

Humidity determines how much or how little water your marijuana plants are going to allow to evaporate.

If the humidity is too low, the evaporation pressure will be higher, meaning your plant is able to absorb water and nutrients at a faster rate.

If this rate gets too much, however, your plant will close its stomata, so it doesn’t lose all of its water and become dehydrated.

At this point plant growth will have slowed, meaning it is crucial for you to maintain the perfect humidity level.

How to fix a climate problem

When it comes to humidity, a dehumidifier is the best way to solve the issue in a closed system.

Dehumidifiers are equipped with cold tubing that simply condense air moisture, therefore decreasing the humidity level of the room.

They could have the opposite effect when it comes to heat, however since the machine itself gives off some heat and, therefore, could lead to your grow room actually being too hot.

Signs of climate problem on marijuana plants
Signs of climate problem on marijuana leaves

One simple way of avoiding this is by adding some air vent tubing to the spot where the dehumidifier’s exhaust comes from.

This will direct the heat to a place that doesn’t increase your grow room temperature.

If heat is the original problem in your grow room, you should make sure to cool it down before it turns into a health problem for your plants.

Adding ventilation is a good way to decrease the heat level, as is placing an air conditioner into your grow room set up.

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Another way of dealing with the problem is, sometime before the flowering phase of your plants’ life cycle begins, installing an air cooler.

It evaporates water, therefore making the overall temperature of the room cooler.

It doesn’t add a significant amount of moisture, so humidity will not be out of control and have a high level of efficiency during your plants’ vegetative stage of growth.

Make sure you don’t use it while the flowering stage is occurring, however, as it could make the level of moisture too high for your plants to be content.

signs of Heat stress high temperature marijuana leaves
Heat stress high-temperature marijuana

To reduce excess heat, remove any equipment that produces heat and doesn’t need to be in the grow room. Some examples of this are large pumps or light ballasts.

If your plants are grown in a hydroponic growing system, you can change the temperature of the plants themselves in contrast to the exterior temperature.

This is done simply by lowering the temperature of the water your plants are growing in.

Keep the water cool by using aquarium water coolers, which handle this process automatically.

A good rule of thumb is to reduce the water temperature to somewhere in the 60s (between 15 and 20 degrees Celcius) if the air temperature is somewhere in the 80s (between 27 and 30 degrees Celcius).

Preventative measures are the best way to keep your grow room temperature from becoming a problem.

You can get lights that are either air or water-cooled, therefore keeping the heat produced out of your grow room.

It basically just uses tubing to redirect the heat produced by the lamps outside so the same amount of heat can be produced without actually affecting your grow room.

Marijuana plant symptoms

  • Leaf edges curl upwards
  • Yellowing leaves
  • Brown spots on leaves
  • Leaves nearest light or heat affected
  • Leaf burns
  • Slowed growth

In case you have significant differences in temperature between nighttime and daytime, you can simply reverse the lighting order.

Keep the lights on through the night (making the cold nights a bit warmer) and keep them off during the day, therefore cooling things off in the afternoon heat.

You will, therefore, achieve a more constant, ideal temperature level for your plants.

Grow room temperature problems

What to do when your marijuana grow room is very humid? The grow space will naturally be humid because the marijuana plants emanate moisture that collects in the garden space.

To get rid of that moisture, the easiest thing you can do is ventilate the room and replace the moisture with drier air.

marijuana grow room ventilation system
Vent out the heat from your grow room

For gardens that are closed systems, a dehumidifier must be used. Dehumidifiers have cold tubing that will condense the moisture in the air and make it less humid.

Of course, they release heat and can make the grow space too hot if you’re not careful.

To avoid overheating, affix some air vent tubing to the dehumidifier’s exhaust so that the heat is pointed outside the grow space.

If the room is both hot and humid, an air conditioner could work toward removing the moisture while cooling the garden.

Make sure to download my free marijuana grow bible at this link and learn how to create perfect conditions in your marijuana grow room.

What to do when your marijuana room is too hot? There are plenty of ways to cool down an overheated grow room. See what suits you best:

  • It can be ventilated to remove the heat.
  • An air conditioner can replace the hot air with cool air.
  • Prior to flowering, an air cooler that evaporates water to lower the temperature can be beneficial. These coolers won’t add too much moisture to the air and are ideal and extremely efficient during vegetative growth. They are, however, not good for plants in the flowering stage because they create too much moisture.
  • If the temperature drops drastically at night, you could solve the heat issues by running the garden’s lights at night instead of during the day.
  • Hydroponically-grown plants can shift temperatures based on how hot or cold the water is. You can keep the plants cool even if it’s technically hot outside. If the room temperature is somewhere in the ’80s (27-30*C), try to keep the water temperature in the ’60s (15-20*C). Growers can install aquarium water coolers to keep the water cool automatically.
  • Any heat producing equipment should be taken out of the grow room is at all possible (e.g. light ballasts and large pumps).
  • Avoiding heat starts from the beginning. Take preventative measures to ensure that heat will not be an issue with your crop. Air- or water-cooled lights keep the lamp’s heat from entering the garden. A series of tubes takes the heat from the lamps to the outside without affecting the temperature in the grow room itself.

Remember that plants with strong genetics have less chance of getting sick and are less vulnerable to environmental stresses. So make sure to buy marijuana seeds from a trusted seed bank.

FAQ about climate problems

What are the most common climate problems when growing marijuana plants?

Some of the most common climate problems when growing weed plants are either excessive temperature or humidity.

What to do when your marijuana grow room is very humid? 

Naturally, the growing room should be humid as the pot plants emanate moisture that gathers in the garden space. The best way to do is to ventilate the area and cover the damp with drier air, and get rid of the damp.

What happens if grow room is too hot?

An overheated growing room will trigger the plants to experience a variety of other problems. Firstly, burning of nutrients may occur at high temperatures by enhanced water transpiration. Mildew can also occur, especially when the room is too humid.

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


Avatar for Robert Bergman

Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

37 comments on “Climate problems & your marijuana plants”

  1. Dennis, First; You should never use 24/0 photo period, and yes, they are going to stretch like crazy and bud in a week or 2 because of the extreme photo period change. Try 16/8 for veg if you plan on replacing them outdoors after veg. Better root production as well during shorter photo period.

  2. My seeds broke soil on 2/15/19.. i grow outdoors but i wanted to cut a shit ton of clones. Well i have about 80 clones and taproot plants that are 5′ tall. Thay been on a 24 hour light cycle and i was worried that when i take them outdoors that thay woll go in to bud becouse of light cycle change ????

  3. My problem isn’t climate it is the little animals in the ground that like to eat roots! My question is: Do gophers eat marijuana roots? I have been growing in wire baskets, (out of doors, of course), and want to
    stop using them. Hey, I enjoy your site very much and the information! This year my plants, (started in the house under a cheap grow light), look great better than last year. Your seeds are terrific!!!

    • Colin,

      Gophers. Never had that issue but, many pets and varmints love this miraculous plant. Keep up the successful growing.

  4. Robby!!! How are you bud?
    Your emails & deals on seeds are the best emails anybody can get. I have gone from a beginner to a begrinner

  5. Hi Robert, love your grow guides, thank you for sharing so much useful information. I am a medioka grower, and appreciate all the extra tips I have found via your website. I often teach beginner growers because my goal is to become a compliance officer in Maine in ref to one of the MMJ/MJ compliance fields. If you happen to know of any recognized training programs in Maine (or similar compliance matching state such as Colorado where I plan to tour/train as soon as funds allow me to do so) could you pass this on to me. I am anxious to learn and find a compliance driven career, having several years experience in ISO standards and management level experience. I’ve been growing marijuana myself for approximately 4 years, and prior to this, received hands on training for about 10 yrs (ex-spouse), just for a little insight of my goals. I enjoy growing, but often find I am leaning towards googling more than anything, googling laws and compliances, and grow tips combined. lol Which leads me to striving for a focus in one area or the other, as limited time allows me to only choose one focus, for better focuses, and I know I’m stretching my luck trying to “do it all”, so to speak.
    just sending along typo found on your site as a courtesy.

    Remember that plants with strong genetics have less change (typo) of getting sick and are less vulnerable for environmental stresses. So make sure to buy marijuana seeds from a trusted seed bank.

    Thank you so much for your shares and your time.

    Registered Maine Caregiver

  6. I have a question. My plants look exactly like the photo at the very top of this page. I’m growing in soil outdoors. Is the photo of a heat stressed plant? How can I fix this befor it destroys my entire plant? Thanks in advance

  7. Heather,

    You all are definitely on the right track. You will have better success if you use AC. AC can also help keep the RH in line. The idea of purchasing a humidifier is a good one. Make sure to buy a good unit. You will be happier in the long run if you purchase a unit that will last. Perhaps a unit that would cover a bigger area than the room you are using.

    Happy growing. Join our support forum for great info anytime. 🙂

  8. Vinny,

    Anytime you add a much more intense light to the plants, they will sqwuat and take more nutrients putting energy into new root growth which apears to present as not growing, or slow growth.

    This article is about environmental issues of plants. It is not about LED light theory.

    Perhaps you would be better served by joining our support forum, where we have many experts will to share info in a friendly and mentoring atmosphere.

    See you there.

  9. George,
    I suggest you join our support forum. This blog is not set up for this type of Q and A mentoring. Join us at the forum and we will share all kinds of info regarding your issue. 🙂

  10. Climate is a big concern for me in Las Vegas. Our humidity in general is about 8%. And of course, keeping my house cooler than 78 in the summer is outrageously expensive. I’m anticipating installing an A/C unit in the room I’m going to use for the grow, and adding a humidifier to add humidity because unless we’re having a monsoon, we just don’t have any. Any other suggestions for dealing with growing in the desert?

    • Hi Heather, I am a fellow grower in Vegas, and the humidity within my room has not really been a problem at all. Given the temps in the room and the moisture from watering and from wet soil, my humidity level stays great as long as i keep my inline exhaust on a timer and down as low as it goes when it is on. I am running 8500W of full spectrum LEDs. I do have a portable air conditioner with a digital, programmable thermostat that has worked wonders, and a wall-mounted oscillating fan for circulation. With the portable a/c and LED lights it is relatively easy to maintain great temps.
      On another note, one advantage we have here is that if you supplement your ladies with CO2 they will actually thrive in temps between 85 and 95 which makes it that much easier and less stressful in the dog days of the Vegas summer. Hope this helps! Happy Growing!

  11. My question is, “when switching over from cfl lights to LEDs, is there a time of adjustment for the plants”?You see, I just bought a 1000 watt LED setup that is AMAZINGLY BRIGHT! Now the plants love it (one blueberry and one AK-47, and they are bushy as hell from the cfl, but they don’t seem to be responding yet. They have been under the light for about four days now. How long will it take before they respond. By the way, they are both auto fem plants, and two weeks have already gone by, and they 3 1/2″ for the AK, and 3″ for the blueberry. Will I be stuck with small plants, even though they are very bushy and new side shoots are coming out all the time?

  12. Double check that the plant isn’t a male. It may have hermied if it was stressed. Pretty common for newbies. Did it come from a clone or seed?

  13. I’ve been growing indoors for 9yrs, from hydro to soil, different strains, nutrients over the years..Products/Info, clones improved but I didn’t upgrade my ballast/lights until last summer…finally traded up from x8 1000watt old school lights to x3 Phantom DE commercial dbl-end system. My last run w/32 plants was great w/8.5# of premium NorCal Blue Dreams and plenty of quality trim for oil, that run finished in Oct, I run my lights at night, sometimes have to use A/C, etc, but no problem that run w/temp or humidity. I didn’t start next run until Feb., due to upgrade, etc…the clones are suppose to be LA Khan/Gorilla Glue x, but IDK…Didn’t get from my usual sources. Initial pre-veg took longer than usual 5-6 wks & didn’t transplant (2nd x) to my 10 gal pots until wk 8. I use 100% top shelf soil (don’t add anything) Then 2nd Veg stage (big pots/big room) was taking way too long (usual 4 wks max to let plants get 5x bigger) they looked healthy, just smaller than I had ever had. Finally triggered all x43 plants, did normal clean-out 15days later, and then waited. I use a full schedule Nutrient System from Emerald Garden, plus Silicone Shield and Magnessium bump 1xwk…water by hand every other day (I like hanging w/my girls..I can spot-fix little stuff right away) so what’s the PROBLEM??!: I did not fully anticipate how cold the room would be w/out the x8 old-school bulbs heating it up…the new ones put very little heat out (had to run cool air duct through old ones, these don’t even have glass cover – of course I still also draw fresh air in/out via filters through the room 24/7) I am I week 7.5….very sadly, the buds look like week 3, no real change in 2 weeks. I had a flying gnat prob., but the plants are dark green/healthy, just no bud growth! As a veteran, I am embarrassed to ask the probably obvious: ‘Are my girls going semi-dormant due to the cooler temps’? It’s been unusually wet/frigid here this year…Would a heater help, if so, what style/type/brand would you recommend? Always had to cool the room to keep it at cozy 70-75deg., not much Info @ too cold in a room available! So frustrated w/lack of progress, ready to chuck it and start over, w/strain I’m familiar with..but, is it the plants dna or ?? Thank for any advice..=^..^=

  14. Help please…im newbie and not sure of the larger juvenile has 2 leaves the are like sad…the others are perky..

  15. Weedrater,

    Fan leaves are the heart and the lungs of the plant. Although you can finsih a quality plant this way; Yield will suffer due to the stress caused by removing all fan leaves.;


    Happy growing

    • ..not to mention the amount of energy the plant uses from the leaves at end of life, to fatten the buds up defo yeild effected.

      • don’t cut the fan leaves, they are the factory within the plant. That’s why its stopped growing no factorys no growth. Eventually the plant will try regenerate but it will cost you a few weeks.

    • Removing alot of fan leaves gives your a plant bigger buds. Just need to cut the right ones.

  16. my outdoor plants the leaves will stand straight up and be completey dead by moring there are no spots no yelling no pest any one have a idea or solution

    • patricia,

      I suggest you download and read our free “Grow Bible”; Better yet. Join our free grow support forum where we have many experie3nced members and experts to help you succeed from seed to harvest.

  17. My buddy took me 2 his garden and he had cut the fan leaves off and left leaves on the branches, he said the buds will grow good now.I don’t know they looked like skeletons to me. Any ideas on this?

    • I cut all fan leaves after the plant reaches 2 foot. It give more light to the branches that produce Colas and gives extra nutrients and minerals to the plant itself. Don’t forget to low stress train and don’t desolate to soon on the branch leaves.