The Ultimate Temperatures For Growing Cannabis

We humans like comfortable temperature levels in which we can enjoy our daily lives. Well, cannabis is no different. Optimal temperature levels need to be maintained throughout its growth to create exquisite bud, ready for experiencing.

During the vegetative stage, the cannabis plants feel most comfortable somewhere between 21-29°C. And during flowering stage between 18-26°C.

The temperature fluctuation should be around 6°C between the night and light cycle. So in the vegetative stage between 21°C during the night (lights turned off) and 27°C during the day (lights turned on). In the flowering stage, the sweet spot is around 18°C at night and 24°C during the day.

Once you have decided on your location to grow, the choice of the cannabis strain can make or break your desired outcome, due to climate circumstances.

If your plants are experiencing unbearable Sahara temperatures or freezing to death like Leo in Titanic, here are some solutions to temperature problems:

TOO HOT

If it's too hot during the flowering stage, app. above 26°C, buds start to lose their potency and smell due to terpene evaporation. Terpenes are responsible for the smell and taste of the bud, as well as cooling the plant and repelling pesky pests. It's especially important to keep the temperature at accurate levels between week 6-7 in the flowering stage because that's when terpene production kicks off.

In high temperatures, the plant is suspect to spider mites, powdery mildew, nutrient burn, root rotting, stretchiness and wilting. If it's hot and really humid above app. 70RH you can expect mold.

Generally, really high temperatures will stagnate the growth of the cannabis plant, and in extreme cases completely extinguish its existence, which is obviously unacceptable.

So, let's see some solutions!

1. INDOOR PLANTS

Aircon

It's a great device to cool down the air, for satisfying temps. It blows cool air into the desired environment and pushes out hot air from the other side, so you need to make sure that the hot air does not enter the growing space because then the purpose of the aircon will be self-defeating.

Swamp Cooler

Swamp cooler emanates cool air like an aircon, but also raises the humidity of the room. This is a perfect solution for hot and dry spaces.

CFL

The light illuminated from CFL light bulbs functions to grow cannabis. These light bulbs don’t generate much heat, you can have plants couple of centimeters from the CFL light and everything will be grand. This solution is great if you are limited to a small space and in need of a stealthy operation. I would recommend this solution for max. 3 plants.

Lamp Cooling

Air-cooled lamps function great, the heat generated around the lamp gets directly pulled out. Water-cooled lamps work in the same way, although water flows between the outer space of the glass frame which eliminates up to 93% of the heat, generated by the lamp. If you have heat problems and don’t have either one, this is probably the cheapest and most effective way to lower the temperature significantly.

Light Cycle

If it's too hot during the day, it would be smart to put the night cycle during the timespan when it's the hottest. For example, lamps turn on 12h during the night and turn off 12h during the day, during the flowering stage.

CO2 enrichment

With higher temperatures 30-35°C, you can consider adding extra CO2 in the air, which would give a nice boost to the growth. The yield can increase up to 20%! Although, be aware, this technique is expensive and not suited for beginners. Complete control over the environment in the growroom is essential.

Air Circulation

You need to have good air circulation in the tent. Inside you need to have fans which circulate air to provide the plants with fresh air and a nice breeze. The exhaust fan should be successfully eliminating hot air from the tent, and there should be fresh air coming in from the bottom.

2. OUTDOOR PLANTS

If you are growing outdoors in a hot climate with optimal humidity levels, longer flowering strains are a better option. Although, if the heat becomes uncontrollable, faster flowering strains are better suited.

It is obviously much harder to control the temperature for outdoor cannabis plants, but it's not impossible to improve the temperature conditions.

Into the Ground!

The ultimate solution is to put the entire plant directly into the ground, although you need to make sure that the soil is habitable for cannabis. Underneath the soil surface, the heat does not penetrate as it does in pots, the plant can handle as much as 40°C in the right circumstances! If it's really hot, keep the roots nice and cool.

Plants in Pots

If your plants are in big pots, in a hot climate, the pot might get super-duper hot, which will heat up the roots and therefore be disastrous for the plant. A solution is to paint the pot with special paint that's designed to reflect heat.

Mulch can also be put on top of the soil to create insulation for really cold and hot temps.

You could put the pot into the ground entirely or partially or simply try to shade the pot as much as possible, without shading the plant. There are many ways of shading and cooling the pots, so smoke a joint and get creative!

Micro-sprayers

For outdoor plants, this is an ultimate option to cool down the plants significantly. These sprayers spray tiny droplets of water, which can cool down the plant, although it's important not to spray too much on the plants, especially when the relative humidity (RH) is on the higher spectrum.

TOO COLD

As a general rule anything below 15°C is considered too cold for a cannabis plant. The plant stagnates in growth and is more suspect to create drooping leaves and discoloration of leaves which reduces photosynthesis. If it's cold and humid you may expect mold. If it's too cold the plant can die completely overnight, like Leo. The plant can still be revived if given some appropriate heat, but it will never grow to its ultimate potential.

So, let's see some solutions!

1. INDOOR PLANTS

Heaters

You can get a heater that blows out hot air, but with these heaters, you need to make sure that they don’t blow directly on the plants. Oil-filled column heaters are a good option since they generate heat around the outer surface without air pressure.

MH/HPS light

Instead of CFL lights, you could upgrade to a MH or HPS light, which will generate more heat.

Light Heat

You could also remove the air-cooled lamps glass plate so that the lamp will generate more heat, although be cautious of the heat, the temperature difference can become app. 6°C higher.

Heating Mats

You can place heating mats underneath the plants to provide additional heat for the roots. These are mostly used for smaller growing operations.

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Heating Cables

These cables are also used to heat up the soil. You want the heat to be distributed equally in the pot, so you might want to place it underneath a heat distributing material which is in contact with the pot. This technique is also best suited for smaller operations.

Insulation

You could use insulation systems to keep the heat in the tent, and the cold outside.

2. OUTDOOR PLANTS

Short Lifespan

If you are growing in a colder environment such as Canada or Northern Europe, where the spring comes late and winter comes early, the cannabis strain should have a short flowering period.

That is, to shorten the amount of time when the plant can be exposed to really cold temperatures.

Polyethylene plastic

You can cover the plants with polyethylene plastic, this will keep things nice and warm during the night, but you need to let the plants breathe! So uncover as much as possible during the day.

Gas patio heaters

You can use gas patio heaters for outdoor plants, to provide the higher temps and coziness they deserve, during cold breezy nights.

Miguel Antonio Ordoñez

With an AB Mass Media and Communications degree, Miguel Ordoñez is a veteran writer of 13 years and counting and has been covering cannabis-related content since 2017. Continuous, meticulous research along with personal experience has helped him build a deep well of knowledge on the subject.

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