Low And High Temperature For Marijuana plants

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Ideal Temperature For Marijuana Plants

Ideal Temperature For Marijuana Plants

Marijuana grown indoors functions better at moderate temperatures between 70 and 75*F (21-23*C) during the light period and a drop of no more than 48.2*F (9*C) to 60*F (15*C) during the dark period. CO2-enriched plants will produce more at a marginally higher temperature of just under 80*F (27*C).

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. 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.

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.

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. Gas patio heaters can keep gardens warm on frigid nights. Maintaining a temperature of 60 degrees will promote plant growth substantially.

These outdoor plants can also benefit from a polyethylene plastic covering that keeps things nice and toasty while also protecting the garden from the elements. Heaters can increase protection even more. Download my free marijuana grow guide at this link  for more tips & tricks.

Most plants can withstand high temperatures if they have a large root system that can bring up an adequate amount of water to keep the plant comfortable during transpiration. During vegetative growth, temperatures that extend into the 80’s and 90’s (27-37*C) can produce elongated stems. During flowering, it can produce airy buds. This is the same for both indoor and outdoor marijuana plants.

For indoor plants, you can lower the temperature with ventilation, air conditioning, or by using air- or water-cooled lights that eliminate heat. Just to be clear, it isn’t the temperature in the aisles of a room that you need to worry about; it’s the temperature directly under the lights at the plant canopy level on which you need to focus your attention.

For outdoor plants, you can cool the air with micro-sprayers that lower the temperature by an average of 20 to 30 degrees during the day. The spray emitted is full of droplets that are 5 microns or less in diameter. The droplets evaporate, providing a cooling sensation in the surround air.

Outdoor plants that are kept in small pots or small planting holes that are surrounded by poor soil will have a difficult time growing even if the soil is moistened regularly. This is largely because their roots are often smaller and less abundant and cannot draw water to the leaves. The roots can also be overheated if they are in containers that absorb light and produce heat.

First, check to see if the plant happens to be root-bound. If it is root-bound, then you should transplant it to a heftier container. To avoid overheating, paint over dark containers with light colors that will reflect instead of absorb most of the light.

If you see tip burn or if the buds closest to the lights are stretching and appear bleached, the area directly by the lights is too hot. Tip burn is occasionally misdiagnosed as too bright of a light. The intense light is fine; the heat is what gets to the buds.

For a quick fix, just keep the lights farther away from the plants. 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.

For the most part, loon-watt lights should maintain a distance of around 3 feet (1 meter) from the tops of the plants. Air-cooled lights make the acceptable distance range between 18 and 24 inches (45-60 cm). Water-cooled lights make the acceptable distance about 12 inches (30 cm) or even less from the plant tops. With light movers, you can move the lights closer or farther away depending on your preference.

Check out my marijuana seedshop  for a wide selection of top-quality seeds. We ship to the United States, Canada, and 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. And don’t forget to download my free grow guide 😉



Comment Section

18 thoughts on “Ideal Temperature For Marijuana Plants

By GeoBot on 31 May 2014

Good Info, Thanks

By chrissy on 9 October 2014

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

By sam and maria roberts on 2 November 2015

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

By Ed boham on 20 May 2016

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

By perfectgrowth on 25 August 2016

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

By Chapito on 9 July 2016

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.

By Nick on 4 November 2016

Yes I have a 15 way led and it works great

By latewood.ILGM on 3 November 2015

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.

By BotanicMike on 6 November 2015

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!


By T Bear on 20 May 2016

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

By Joao Ferreira on 26 May 2016

You mention temperature what about humidity ?

By Gongalee on 27 May 2016

Great info, well appreciated.

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