How does the cold affect cannabis plants?

Cannabis varieties react differently to cold, although below a median temperature of 12ºC they are universally at risk of death. As with water, which at higher temperature contains a lower concentration of dissolved oxygen, once the air cools to below 18-20ºC the plant's metabolism will slow down gradually and hinder or halt development.As the plant's metabolism slows down everything becomes much less active. The bio-chemical and enzymatic processes required for healthy growth cannot take place and vegetative vigour disappears leaving plants small and weak. The root system cannot function as it should, rendering it unable to absorb adequate nutrition. This will have an obvious negative impact on yields, leading to very small buds and vastly reduced production.

As previously mentioned, low temperatures will detrimentally affect the root system and the uptake of nutrients, particularly in the case of magnesium. This micro-nutrient is vital for the proper development of the cannabis plant and if the substrate is colder than 18ºC then this element is most likely not being absorbed by the plant.

If, in addition to a low cultivation temperature, the growing medium is over-irrigated or water-logged, then the plant will be completely unable to take up magnesium, leading to visible deficiencies in the larger leaves, which even the application of magnesium in every watering will be unable to solve.

As we can see, controlling the temperature of our grow is integral to a successful cannabis harvest and there are various options available to help us do this, adaptable to each grower's needs based on dimensions, ambient temperature, lights used etc.

How to avoid low temperatures indoors

Switch Lighting Periods

Indoor HID lighting can cause problems during the summer because of the heat they produce. Use this to your advantage during the wintertime by running your 'lights on' period overnight when ambient temperatures are cooler, and 'lights off' during the daytime. The heat produced will help towards counteracting the cooler nights.

If plants are still in vegetative growth when winter takes hold, growers should also consider increasing the 'lights on' period from 18 hours to 20, 22 or even 24 hours. This will just give them a little more heat protection during the cold.

Adding more Light

Adding additional light to your set up is one of the most efficient ways you can add extra heat to your grow environment. The extra light will act as a heat generator keeping the temperature raised during harsh conditions and your plants are sure to thank you for the additional lumen output! As winter slowly creeps upon us, expanding your lighting set up is crucial to ensure you can get the most from your plants without worrying about heat.

Use Secondary Heating

With that said, the heat produced from lights is generally not enough to ensure your grow room is at the optimum temperature, so secondary heating is usually a must! Originally designed for greenhouses, Tube Heaters are small enough to be easily placed at any level within your grow room. With super low running costs, the Smart Gro Tube Heater lets out a consistent spread of heat in the surrounding air, keeping your grow room at a steady temperature.

Tube Heaters are not thermostatically controlled, so if you want that option then Oil Filled Radiators are a compact yet powerful way to establish optimum temperatures and can be used inside a indoor grow tent or room, causing no detrimental effect to the plants. 

The third option is a Fan Heater, although these should be used with caution as the dry, hot air can lower humidity, damage plants and impede growth if blowing directly at them. We recommend they should only be used outside the grow tent or room to warm up the surrounding air, or directed towards the intake. If the only option is to have it in the grow space, make sure it isn't pointing directly at the plants, or consider changing it to an Oil Filled Radiator. 

Give your plants some warmth

Your plants may need some help to protect themselves from temperature spikes and really flourish to their maximum potential during the winter months. Vitalink Heat provides a great solution to that problem, a small amount can last a very long time. Using heat before the cold really sets in can help your plants develop a resistance to the cold. Use heat sparingly as overdoing it can negatively affect your plants, sticking to the recommended amounts or even slightly under can really provide some peace of mind for you during these cold months. Directions can be found on the bottle and on our website.

Watch Your Intake

If you're drawing outside air into your grow room, you're bringing the cold in and making it harder for your plants to stay warm. Move your intake fan so you're drawing air from indoors, making sure it's from a different area to the grow room. There's also an additional advantage in that air being drawn from inside will not only be warmer, but also richer in CO2.

You can also use a fan speed controller on both your extraction and intake fans. During vegetative growth and early bloom, turning the fan down by a few percent will allow the warmer air to stay in the room for longer whilst still refreshing often enough for plants to thrive. This, however, might not be an option if in mid to late flower as unwanted grow room odours might require the extraction fan to be on full, therefore secondary heating, as outlined above, should still be considered.

Keep an eye on that temperature

Plants thrive in temperatures between 25-28°C during lights on, and around 18-21°C whilst lights are off, so it is important to check your temperatures regularly to ensure these conditions are consistently being hit. Simply keep an eye on temperatures and humidity in your grow room with a Digital Thermometer and that way you can work quickly if something needs addressing.

The biggest advantage of having an indoor hydroponics system is to allow you to grow all year round, but that doesn't mean your plants are safe from wintry temperatures. Taking these simple steps will ensure that you get optimum results no matter what the weather outside is.