The Perfect Temperature For Growing Marijuana

Last updated: 25 May 2020

best temperature for flowering stage

Imagine that you’re always too hot or too cold, and that you’re unable to move or even produce your own body heat. Sounds strange, right? That’s the life of a plant!

Because plants cannot regulate themselves, temperature is a top priority when it comes to both growing cannabis plants and the quality of your harvest. Controlling your grow room temperatures will help you grow healthier, happier plants that yield better quality bud. This article will explain the best temperatures for growing weed, as well as some easy-to-implement tactics to get your grow room temperatures under control.

Does Temperature Matter?

The temperatures that a cannabis plant grows in are extremely important, as they affect how efficiently a plant can move hormones around its structure. Too hot or cold, and the plant will have a hard time delivering sugars to where they’re needed, resulting in stunted growth.

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What If It’s Too Hot?

cannabis temperature

If temperatures are too hot in the growing environment, the cannabis plant will suffer from heat stress, causing stunting of growth and poor branch structure. If high temperatures persist into the flowering phase, they can also have negative effects on the smell and potency of the finished buds, as well as prohibiting them from forming nice, dense nugs, instead developing loose and airy flowers.

Moreover, if the grow light is too close to the canopy, it can sometimes directly burn or bleach the tips of the plant, which severely impacts growth.

Or Too Cold?

what happens to a plant if the temperature is too low

Cannabis plants will also suffer if their environment is too cold. Like with heat, stress from the cold can stunt growth by inhibiting the movement of growth hormones to the tips of the plants.

Unlike with heat, which is unlikely to directly end a harvest, cold snaps like frost and snow can certainly kill cannabis in the space of a single night, so care must be taken to ensure temperatures do not drop below freezing in the growing environment.

So What Temperature Is Just Right?

When we talk about the ideal temperatures for cannabis growing, you should know it’s not just a single number. Just like with most living things, cannabis requires slightly different temperatures depending on its stage of development. 

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Seedlings And Clones

marijuana growing temperature

During the clone or seedling stage, the cannabis plant needs a temperature between 68-77°F (20-25°C). It is best if this temperature remains stable, as this helps roots develop quicker.

A great technique is to use an electric heat mat under your seedlings or clones to provide a stable temperature that can be digitally set.

Vegetative Stage

temperature for growing weed

Once your cannabis plants reach the vegetative stage, they can handle a bit more temperature fluctuation. However, their ideal growing temperature is still between 68-77°F (20-25°C).

If you’re growing cannabis outdoors, your plants will be able to withstand larger temperature swings as they adjust to the day/night cycle of their environment. Indoor plants remain a bit more delicate, ideally suited to a relatively constant temperature, although they too can handle slightly lower nighttime temperatures.

Flowering Stage

grow room temperatures

The best temperature for the flowering stage is still between 68-77°F (20-25°C) during the light cycle. However, an advanced growing technique is to drop the temperature in the growing environment by roughly 10°F at night. This helps certain strains of cannabis fully display their specific phenotypes, including colors, terpenes and cannabinoids.

Even if you don’t feel the need to drop the temperatures at night, make sure you stick to temperatures consistently under 82°F, as above this, some terpenes begin to evaporate.

Drying And Curing Stages

grow room temperature too high

Ideally, a dry room or box should be held at a consistent 64°F (18°C), which allows the buds to lose moisture slowly and evenly, leaving them smelling fresh and feeling nice instead of being brittle and crumbly.

As well as temperature, it’s important to keep your drying buds out of sunlight, as this will quickly degrade the cannabinoids on the plant material. Make sure they have adequate airflow as well, since this prevents mold from forming on the bud.

Are Digital Thermometers Better?

what temperature is too cold for plants

When it comes to measuring the temperature of your growing environment, how should you do it?

When measuring the temperature for growing weed, the only tool you need is a thermometer. These give you a precise reading of the temperature and are readily available for relatively cheap. There are two kinds available; analog and digital. If possible, go digital, as they usually offer a lot more features such as instant readouts, storing highest and lowest temperatures, and some even come as a thermometer/humidistat combo, allowing you to check the humidity at the same time.

Once you’ve got your thermometer, simply place it somewhere near the height of your canopy and wait for the readout. Another little tip is to find a thermometer with a wire sensor, as this allows you to have the sensor in the grow room during the dark period while keeping the display outside for you to monitor.

Keeping The Temperature Indoors And Outdoors

Although it might seem like a major hassle, once you’ve got control of your cannabis gardens temperatures, your plants will show enormous improvement, both in their overall health and at the rate they grow. Here are some tips on how to keep these temperatures in check.

Outdoor Gardens

best temperature for growing weed

If you’re growing outside, you first need to know that regulating temperature is less precise than when you’re in a fully controlled environment. You’re essentially moving the temperature up or down rather than aiming for a specific number.

In saying that, there are some simple methods of controlling your outdoor garden temperatures, both during the hot summer months and as it edges colder toward winter.

If your environment is too cold, constructing a simple greenhouse or glasshouse will help tremendously with raising the temperatures. If your budget is small for this, you can build a simple polytunnel with plastic and PVC piping for next to nothing.

If it’s too hot, however, you’ll want to invest in some additional shade for your garden, but without completely blocking out the sunshine. Shade cloth structures are excellent for this, as they allow sun through while dropping the temperature underneath. Likewise, trees that cast partial shade over the cannabis can also be beneficial in hot, harsh environments.

Indoor Gardens

ideal temperature for cannabis

If you’re growing indoors, you have much more control over environmental temperatures. Instead of simply moving them up or down, you can dial it to exact degrees. The flip side of this, however, is that indoor temperatures can blow out extremely quickly, threatening your harvest.

Luckily, an indoor garden's temperature is easy to control if you have the right tools. Running extraction fans, as well as vented lighting, will help to move any hot air out of the environment before it builds up. If you’re able to run intake fans, place them low down and make sure they’re drawing from an area with stable temperatures, as this keeps the grow room stable as well and helps to flush out stale air.

Inside the room, airflow is extremely important for temperature regulation, as it stops hot air building up around the canopy or light. If possible, have a fan directed right across the canopy, as well as one directed from the ground up through the branches, to ensure complete air circulation.

Is It Worth It?

Like with many aspects of growing, cannabis temperature is an extremely important factor in bringing in a beautiful harvest of dank buds. While it may be confusing at first, within one grow, you’ll be able to fully understand the fundamentals of temperature control – and once you’ve mastered this skill, you’ll be able to take good quality genetics and turn them into great quality cannabis.

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