Top Tips For Growing In Cold Conditions

  • Published on September 30th, 2019
  • Category: General

Maintaining your plant’s environment is key to a successful grow, poor environments lead to poor quality and small yields. Keeping conditions within optimal ranges is one of the biggest challenges for growers, the UK climate is notoriously varied. However, colder months are ideal for growing, because it’s much easier to add heat than it is cool your grow room down (without the cost of full air-con units). The guide below will help you understand the perfect conditions, and suggest the best products to help you achieve them.

Plants and air temperature

Plants like their air to be kept reasonably temperate. As the colder weather begins to draw in, it can be difficult to keep the air around your plants in the sweet-spot of 23C – 28C (28C being the absolute maximum temp you ever want at the tips of the plant without CO2 supplementation)

23C-28C is the ideal temperature only during the lights-on period. During the dark-period a few degrees of temperature drop is desirable to simulate natural conditions, although the temperature should ideally not go below 18C, and should never go below 15C.
Obviously, a grow lamp creates quite a bit of heat. While this can cause problems of high temperature during the summer months, it is actually a very useful side-effect during the winter.

For most growers, the simple addition of a fan speed controller (check out our range) to reduce the amount of hot air being exchanged for cold air within the grow environment, is enough to keep the air within the right limits. As long as enough air is being exchanged to refresh CO2 levels and to keep humidity moderate then this approach can be a great solution to keeping temp in the 23C-28C range during the lights-on period.

When the lights go out

Temperature during the dark-period is something that many growers do not consider. Maintaining the right temperature during the lights-off period is just as important as getting the temperatures right when the lights are on. As stated before, while it is a good idea to have a temperature drop of a few degrees during the lights-off period, it is important to not let the temperature go below 18C and it is absolutely vital the temps NEVER go below 15C.

Plants sense the temperature even during the dark-period. A temperature drop during the lights-off period actually helps plants to respond better to the photoperiod. A drop of a few degrees when the lights go out will help kick plants into flowering/fruiting more quickly when they are switched to 12/12, and promotes stronger flowering/fruiting thereafter.

Brrrr It’s cold, winter must be coming, I think I’ll stop growing now…

Plants use temperature to sense when winter is coming. Plants also need certain temperatures for the biological act of living and growing. Plant growth goes down markedly below 18C and plants can “stall” (stop growing completely) below 15C. It may only take one or two cold (sub 15C) lights-off periods for the plant to decide that winter is coming. This sets off a process whereby the plant ends flower/fruit bud production, finishes-up the flowering/fruiting maturation process in a hurry, and then gets ready to die or recede until the springtime.

If plants “stall” in this way, it can take up to 2-3 weeks for them to get back to normal flower/fruit production. Usually, they will never recover what has been lost during the “stall” period. As I’m sure you can imagine, 2 wasted weeks out of an 8-week flowering or fruiting period will have a huge detrimental effect on the size of the final crop.

Keep them snug

So that your plants do not “stall” or slow down during this critical period, it’s a very good idea to have a method of keeping the air warm within the grow-space, even during the dark-period. Fortunately, there’s a couple of easy ways to do this, and it doesn’t have to break the bank.

First of all, there are the tubular “Greenhouse Heaters”. These bazooka like objects are designed to take up very little space in a grow-tent or other grow space. They are available in a range of wattages to suit the size of your tent/grow-space and how much heating will be required. These devices will certainly keep the chill off without you having to re-arrange your whole tent:

Lighthouse Ecoheat – Click Here 

They’re great for most situations, but aren’t thermostatically controlled (they do not switch off when a certain temperature is reached). So we’d would recommend the addition of a wireless thermostat, so they kick in and switch off at the right temperatures.


For added control, a small oil-filled radiator featuring a thermostat is the way to go. Although better than nothing, because the built-in thermostat sits directly on the radiator it’s not the most accurate, so for better results we’d recommend a wireless thermostat. This little one will fit into virtually any tent and will keep temperatures just right:

Oil-filled Radiator Click Here

Lighthouse 2kw Greenhouse Heater (23cm x 19cm x 32cm) – Click Here

It’s not just air temperature – it’s your nutrient solution too!

If you have a reservoir in your hydroponics system, it is best to keep your nutrient solution at about 18C (65F). It is not just cold air that can cause slowed growth in plants, the temperature of their feed water too can cause it too. Again, anything below 18C could begin to cause problems. Anything below 15C and there is a definite risk of stalling.

Fortunately, a simple aquarium tank heater can do the trick:

We stock several size/wattages to suit any reservoir.

50W – Up to 25 Litres
100W – Up to 75 Litres
150W – Up to 125 Litres
200W – Up to 180 Litres
300W – Up to 280 Litres

They’re really easy to use. Just set the temperature, fit it (submerged) to the side or bottom of your tank and plug it in.

Adding another light

One of the easiest things we always recommend is that you add another light into your setup. Adding another light will give you some added heat which can help to keep your temperature higher during cold periods. Winter is the perfect time to really push your lighting setup and yields to their max as you don’t have to worry about your temperature being unbearable due to external heat like you do in Summer. It’s the ideal opportunity to boost your quality by adding in CDM lighting. The Maxibright Horizon between two HPS fixtures makes a huge difference.

Protect your Root Mass

Keeping your root mass warm is another way in which you could easily help to keep your plants happier during the cold. Your roots act as the engine for your plant, and you want them to be in the optimum conditions all the time. As we all know, heat rises, meaning the bottom of your tent is likely the coldest area of your grow room, but there’s a few things you can do to help. The first thing would be to invest in a nutrient heater. This would keep your solution at an ideal temperature which in turn would maximise nutrient uptake throughout your plant and keep your yields to their max.

Another simple thing you could do is raise the pots off the floor ever so slightly to insulate the bottom of the pot. You could use a layer of polystyrene to raise it up an inch or two (if your system will allow you to), this slight adjustment would make a huge difference to the temperature of the roots, keeping them that little bit warmer.

Cut out Cold Spots

Another fantastic way to get the air circulating in your room to reduce the chance of cold spots would be with a DiffuseAir. Instead of directing air movement straight at plants, it diffuses it uniformly around the grow area, preventing issues with windburn and eliminating micro-climates. This also means it’s perfect for when it’s cold, as it’ll keep the hot air rotating through your grow room when paired alongside a heater to help push the temperatures up. A thermostatically controlled heater would allow you to add some heat to your crop when your lights are turned off (this is also the time in which your tent would be the coolest due to the lack of heat from the lamps).

Give your crop some Heat 

The last thing on our list would be using Vitalink Heat. Heat is a fantastic product which gives you protection from those unwanted temperature spikes and allows your crop to flourish with rich micro-nutrients. A little goes a long way when it comes to using heat in your grow room, so make sure you don’t over do it, as it can have a negative affect on your plants. All guides for Heat can be found on our website or on the bottle! If you’re unsure, go a little under the recommended amount to be safe! You want to be applying Heat into your schedule ideally before the weather gets too cold to allow your plants to become resistant to the cold. It can also be used as a foliar spray (use at 5ml / litre). Tests have shown that plants can keep growing normally at temperatures as low as 5C !!!

With any non thermostatically controlled heating, we’d recommend using the Lighthouse Wireless Thermostat. It allows you wirelessly turn on and off a device such as a heater or fan within your grow room. This gives you the ability to add heat into your grow room should the temperature drop down below a certain level, making it a really valuable tool over the winter period.

Finally, we have the AirComfort, which allows you to monitor your grow rooms conditions from anywhere via an app. This is fantastic for giving you invaluable knowledge that you can use to tailor your environment to maximise your yields.


Hopefully these little tips and products which can save your winter crop have been useful! If you’re still struggling, don’t hesitate to get in touch with us and we can help you identify where you can improve your setup to maximise your yields in the cold!

Happy Growing

Products mentioned in the article

12803   1 kw oil filled rad
£34.95
720790   aircomfort bluetooth wirless temp and rh sensor %28main%29
£29.95
12801   fine elements 2000w radiator
£49.95
Group shot
Choose your size:
DiffuseAir 100

£36.95 £36.95
Heater group shot
Choose your size and wattage:
1 ft (305mm) - 45 Watt

£19.95 £19.95
85346 thermostat lighthouse 1
£29.95
Horizon connet
Choose your CDM kit:
Maxibright Ballast with 930 Elite Agro lamp (flower)

£259.95 £259.95
Heat main offer
Choose your size:
250ml

£23.95 £18.95