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The Best Temperature for Cannabis Seedlings

The Best Temperature for Cannabis Seedlings

Like all living organisms, cannabis plants need the right environmental conditions to survive. Seedlings are especially sensitive to their environment and require a controlled climate in order to thrive. Temperature is one such environmental condition that can have a significant impact on plant health. If your grow room is too hot or too cold, it can stunt the growth of the seedlings or possibly kill them. So, to ensure that you get your grow started off on the right foot, this article will explain what the best temperature for cannabis seedlings is and how you can regulate the temperature in a grow room or greenhouse.

What Is the Best Temperature for Cannabis Seedlings?

The best temperature for cannabis seedlings is between 75 and 80 degrees Fahrenheit, with nighttime temperatures approximately five to ten degrees cooler. Any temperature within this range will support the healthy growth of your plants; however, exposing your seedlings to temperatures well above or below this range may have adverse effects on the plants.

Cannabis Heat Stress

Cannabis plant with heat stress

If the temperature goes above the optimum range for seedlings, the plants may experience heat stress. This usually happens when the plants are exposed to elevated temperatures for an extended period of time.

Heat strain can impede the cellular function of the plants, leading to stunted growth and, eventually, death. Common symptoms of heat strain in cannabis seedlings include:

  • Wilting
  • Leaf curling
  • Stunted growth
  • Dying leaf tips

Cannabis Cold strain

On the other extreme, cannabis plants can also be negatively affected by cold temperatures. If the temperature drops below 53 degrees Fahrenheit, seedlings are at risk of dying. The low temperature gradually slows down the plants’ metabolism, impacting photosynthesis, respiration, and other processes.

Symptoms of cold strain often resemble those of heat strain. If the temperature is too cold, the seedlings may display wilting, yellowing or dying leaf tissue, and stunted growth. And if the plants are exposed to cold temperatures for too long, they may eventually die.

How To Regulate the Temperature in the Grow Room

There’s no question that temperature can have a major impact on plant health. Fortunately for indoor growers, there are several ways to regulate the temperature of the grow room.

Air Conditioners

Air conditioners are one of the most valuable tools for regulating the temperature of the grow room. If your facility does not have an HVAC system, there are several affordable options available.

For most small-scale grows, a portable air conditioner should be powerful enough to keep the grow room cool during the summer months. Portable air conditioners are affordable, easy to use, and easy to move around but may not be strong enough to cool bigger areas. A commercial-grade air conditioning unit may be necessary for large-scale grow rooms with several powerful grow lights.

Heaters & Heat Mats

A heater may be a good investment if you are growing indoors during the wintertime. For most small grow rooms, a simple space heater should be sufficient; however, a commercial-grade heater may be necessary for larger grow rooms.

Heat mats are also a great tool to use for cannabis seedlings. Because the seedlings require a slightly warmer temperature than mature plants do, a heat map may be necessary to keep them within the optimal temperature range. However, if you decide to purchase a seedling heat mat, be sure to buy a high-quality one. Some of the cheaper options have been known to overheat the plants or even catch fire. As a result, it’s probably best to use the heat mat only when you are near the grow room. 


Optimizing the airflow inside a grow room or greenhouse is a must. Ventilation is essential to distribute the temperature evenly throughout the area, prevent microclimates from forming, and aid in gas exchange.

Horizontal airflow (HAF) fans are typically your best bet for ventilating a grow room or greenhouse. Oscillating fans are also effective at distributing the temperature evenly throughout the canopy. Just make sure not to place the fans too close to the seedlings, or their delicate stems may snap.

Shade Cloths

If you are cultivating seedlings in a greenhouse, a shade cloth may be a great option to help control the temperature. External shade cloths can be placed over the roof of the greenhouse, protecting the plants from the heat of the sun’s rays.

For colder climates, an internal shade cloth may be beneficial. These cloths are placed underneath the roof rather than on top of it. Unlike external shade clothes, these tend to provide a warming effect in the greenhouse.

Can You Grow Cannabis Seedlings Outdoors?

Cultivating seedlings outdoors is generally not advisable, as it is challenging to regulate the temperature of an outdoor grow. Most cultivators prefer to germinate their seeds indoors or in greenhouses and move the plants outside once they have entered the vegetative growth phase.

If you are growing seedlings outdoors, it may be a good idea to get them acclimatized by keeping them outside only for brief periods. You can gradually extend the amount of time they are left out until they can handle the heat of the sun.

Measuring the Temperature in the Grow Room

Digital Thermometer

Getting an accurate temperature reading is essential if you want to optimize the health of your plants. Because there can be several microclimates within the grow room, it’s important to place a thermometer as close as possible to the seedlings. Any high-quality digital indoor thermometer should be suitable. It’s also a good idea to place a thermometer in the shade and one directly under the grow lights so that you can identify any microclimates.

Final Thoughts on the Best Temperature for Cannabis Seedlings

If you want to have a healthy and bountiful harvest, mastering the cannabis seedling stage is crucial. Because the plants are so delicate during this growth period, you need to get your environment as optimized as possible. Regulating the temperature is one of the most important factors that impact plant health and is one that can make or break your grow. Fortunately, by following the advice provided in this article, you’ll be able to regulate the temperature in your grow room easily and effectively.

Please feel free to contact us for more information about the cannabis seedling stage. While you’re here, check out our collection of regular and feminized seeds.

What are your favorite tips for regulating the temperature in the grow room? Please share your advice in the comment section below.

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