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Table of Contents

How to Keep Your Cannabis Grow Space Warm in the Winter

Are you trying to keep your cannabis grow space warm this winter, are you not sure how warm it should be or how to keep it warm in the most energy efficient way possible? If so, we recommend reading this article. We will give our suggestions for warming your growing space in the most efficient ways and how to keep your plants warm in the winter time. Most growers are forced to grow in less than ideal condition due to plant smells, and security. This can sometimes cause issues if you are growing in a basement, attic, or cold garage. 

How not to warm your growing space?

First off, using heat to heat your growing space can be risky anytime you are adding heat to a grow room it can come with issues. These can be as simple as overheating the plants to using the wrong type of methods to heat your growing room and burning down your growing space at best and home at worst. For this reason it is important to heat your space correctly. 

Space Heater for Your Cannabis Grow Space
Space Heater for Your Cannabis Grow Space

Space Heaters (With fans)

In our opinion this way of warming your space is the most dangerous of all. These types of heaters work by heating up metal and having a fan blowing through these heated metal rods. This can be extremely dangerous, if the fan quits on the grower these rods are super heated and are responsible for thousands of fires every year. Also they draw a ton of electrical use from the plug, some older homes are not able to handle this draw and it will heat up the in wall wires to the point where they will also start fires. Also never use any type of extension cords with these types of heaters as they are also prone to start fires. 

Cold Cannabis Plant in cannabis grow space
Cold Cannabis Plant Turns Purple

How warm should your cannabis grow space be?

The younger your cannabis plants are the more susceptible they are to cold temperatures. Once the plant is older it will be able to tolerate colder temperatures however this can seriously slow down the growth of your cannabis plants. For this reason it is a good idea to keep your growing space at least 70F (21C). This is not the ideal temperature for cannabis growth, however your plants will still grow just fine.  Cannabis can tolerate temperatures as low as 37F (3C) however prolonged periods at these lower temperatures can cause all sorts of issues, such as nutrient deficiency.  These temperatures can also shock your plants causing them to grow slowly even after the temperature warms back up. 

Some of the best ways we recommend keeping your grow space warm

There are several ways to keep a cannabis grow room warm, including:

  • Insulating the walls and ceiling of the grow room to prevent heat loss.
  • Using a heat mat or seedling heat mat to keep the soil warm.
  • Using a thermometer to monitor the temperature and make adjustments as needed.
  • Using a humidity controller to maintain the ideal humidity level for cannabis plants.
  • Using reflective materials on walls and ceiling to increase light intensity and heat.
  • Using a fan system to move heat around the space.

We will detail each of these methods in more detail below. 

Heat from your Lighting Sources

Using your lights. This seems like common sense, however we see many growers using a super small grow light in their cooler grow space and running a heater alongside it. If you need to run a space heater in your growing space we recommend upgrading your cannabis growing lights to a higher wattage. This will end up producing more heat in the colder months of the year. 

Depending on how cold your space is you may need to have lights that will give off more heat in the winter months and less in the warmer months. This is where having an HPS grow light that will give off lots of heat would come in handy for those colder months. Then switch out your lighting once things start to warm up outdoors. HPS gives out far more heat than LED lighting. These lights can help quickly warm up your growing space and keep it warm in the off hours. This is a much better solution than having LED lighting and a space heater.  

Oil Space Heaters

If you are unable to fully keep your warm with lighting, we recommend using an oil filled heater. These heaters are much safer then the space heaters we discussed above. They come filled with oil that is heated, and then this heat fills the room to keep it warm. These types of heaters are much more energy efficient as well and will continue to keep your space warm even after they have been turned off. 

Oil Filled heater for cannabis grow space
Oil Filled Space Heater

The importance of Keeping your root zones warm

An often overlooked area that needs to be warm is the root zones of your cannabis plants in their cannabis grow space. Even if the cannabis grow space is warm, if the plants are sitting on the cold basement floor the root zones of the plants may be much colder than the rest of the plant. This can be especially important if you are using hydroponic growing methods. If the nutrient solution is cold when flowing over the roots, this can really slow down growth of the plants and can also cause potassium deficiencies in the plants as well if this happens for more than a few hours to a day. 

To fix this issue, growers can use heat mats, for soil or soilless growing pots. They can be placed under the pots to keep the root zones warm. This can really help growth if the plants are in a cooler growing room. 

In hydroponics, grows can use plastic aquarium heaters to keep their water/nutrient solutions warmer. These come in all shapes and sizes, however we recommend the plastic ones that can be placed directly into the solution to keep it warm. 

Using a Dehumidifier to Warm your Cannabis Grow Space 

Another somewhat overlooked option for heating your cannabis grow space is a dehumidifier. Dehumidifiers also come with the added benefit of controlling the humidity in your growing space as well. Humidity can be a big concern for growers, growing cannabis in a cooler space to start with as it can have higher humidity for your plants. This may be fine while you are in the vegetative stage of cannabis growth, however once you start to flower your plants, it can cause mold and powdery mildew on and in your cannabis buds. 

Keeping your Seedling and Seed Starts warmer

It is even more important to keep your cannabis seedlings warm and when starting cannabis seeds. If you are starting cannabis seeds in a cooler growing space, it is a good idea to use a humidity dome to keep the heat in and around your seeds or clones. We highly recommend using a heat mat under your seedlings, and even more importantly under your seed starts. Not doing so can lead to the seeds germinating slowly or in some cases not at all if they are too cold. 

Insulation to Help Keep Your Space Warm

If you are looking to grow cannabis in the winter (or even the summer) in an uninsulated place you may want to reconsider. With no insulation you will be pretty much heating the outdoors as much as your growing space. You will need a ton of heat and most of it will be going straight outdoors. Unless you live somewhere that, the winter does get very cold, it will really be pointless to try and keep a grow room like this warm enough to grow cannabis plants. 

Without grow room insulation your cannabis grow space will also be subject to large swings in temperature. Even with heat, just being turned off for a few hours can dramatically change the cannabis grow space temperatures. In the summertime, growers will have the same issues with heat in the growing space. 

Keeping Your Grow Tent Warm

If you have a very large space that you need to keep warm from growing, but only have a limited number of plants you may want to look into buying a grow tent. This way you will only have to heat the size of your growing tent rather than the entire room for just a few plants. 

If you do choose to go this route, and will need to heat and cool the tent, look for a tent that is bigger than what you need, you will need to provide extra space for the oil heater, lighting, and/or dehumidifier. So keep in mind how much space will be required for your plants and pots but also space for these things in the tent as well. Also you may want some extra space for air conditioning come summer time. 

Cannabis Plant Growing in a Warm Cannabis grow space
Cannabis Plant Growing in a warm room

Final Thoughts

Assessing your cannabis grow space for heating and cooling issues in advance of your cannabis grow space set up can really help with understanding what you will do when the time comes to keep your plants growing fast and healthy with the right temperatures in your growing room. There is nothing worse than coming into your grow room on a cold fall morning and having frozen plants that are in shock and will take days, if ever to get growing again. 

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