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LED Grow Lights in Winter!? 9 Must Dos

LED Grow Lights in Winter!? 9 Must Dos

Alex Grady

Everyone knows LED grow lights are great in summer. They’re awesome in winter, too!

You might have to work harder to control your temperature, but you get to increase your nutrient strength and CO2 usage. The impact on yield is incredible.

Here’s how to get the best out of your LED grow lights in winter.

1) Monitor your temperature

This one’s obvious. As a bare minimum, you should be using something like an Accuread.

AirComfort Temperature & Humidity Meters are great option!

Data is stored in your sensor then synced to a mobile app. All in-app data is plotted into graphs, so you quickly spot temperature trends, dips and spikes.

You can use this information to work out when to:

  • Extract more air
  • Turn heaters on
  • Turn humidifiers on /off

2) Get a heater with a thermostat

The ideal temperature in an LED grow room is 28oC.

In an LED room in winter, you really want a powerful heater. Ideally, one with a thermostat.

The best one to buy is the KlimaHeat Electric Grow Room Heater (digital). It’ll keep your grow room to within 2oC of your target temperature. It’s also really cost-effective. With the digital thermostat, it’s plug and play. It’ll only come on for short bursts of heat, as needed, saving a load of money vs. an oil-filled radiator.

3) Monitor leaf temperature

The ideal leaf temperature is 21oC – 23oC.

To measure your leaf temperature, you can use a laser thermometer, which won’t cost much to buy. In an LED room, they’re invaluable.

4) Get convected heat to plants (air circulator)

LEDs do emit heat. But it’s mostly convected heat. This kind of heat rises above the unit, away from plants.

In summer, it’s easily extracted, which is good.

In winter, you need to get it down towards plants.

A DiffuseAir is a good bet - it will constantly keep the air in your grow room well mixed. If you’re adding CO2, it’ll help keep this evenly dispersed, too.

5) Increase nutrient strength

When your temperature is lower, so is transpiration. As a result, plants need less water. This means you can afford to go higher on your nutrient strength than you would using HID lights in winter.

Just keep an eye on your EC in active hydro systems and use this to direct your EC levels.

In passive or hand watering systems, keep checking leaves. You’re looking for any slight burning of the leaf tips. If you start seeing signs of this, reduce your nutrient strength by a couple of points.

6) Add a CDM or HPS

Both of these are HID lights. They emit radiant heat – the kind that helps keep plants warm.

You don’t need to swap out your LEDs altogether – just add a CDM or an HPS light as a supplemental light.

To make sure your light coverage is right, make sure you:

option a)

a) Slot 1 x CDM or HPS between 2 x LED lights

option b)

b) Slot 1 x LED between 2 x CDMs or HPS lights

7) Reduce air exchange

You’ll probably exchange less air in winter anyway, but when running LED grow lights, you definitely need to.

You still need to extract some air – to work out how much follow these steps:

Step 1

Multiply your tent's L x W x H

The answer is how much space is covered by your grow lights


In an XL BAY6 Tent:

1.2m x 1.2m x 2m = 2.88m3

2.88m3 is the total area covered by your lights.

Step 2

Multiply this by 60.

That'll tell you how much air to extract every hour.


In an XL BAY6 Tent:

2.88m3 x 60 = 172.8m3

A 100mm (4") RVK100 would do the trick!

Step 3

To be really precise, you can:

  • Add 20% for a warm attic
  • Add 20% if using a carbon filter
  • Minus 15% in a cool basement
  • Add 20% for long ducting

8) Add CO2

You really get the benefit of CO2 in an LED Grow Room. Why? Because you extract less air. Any CO2 you add will be in contact with plants for longer before it gets extracted. You’ll be able to achieve a higher CO2 ppm level too.

CO2 is known to increase photosynthesis – how plants produce sugars. An increase in sugar production improves growth and strengthens plants all-round.

Some growers harness CO2 as a way of shortening their growth cycle. Even small increases in CO2 are beneficial. An optimum level of 1200ppm can increase your yield by up to 20-30%!

Just make sure you have a quality fan speed controller with a thermostat. This way the fan will only tick over to create slight negative pressure and keep the CO2 moving around the tent for as long as possible. We suggest Control Freak Dynamic Frequency Controller or GSE Temp and Negative Pressure Controller - both are plug and play.

9) Use intake air from inside your home

Outside air is cold, which isn’t good in winter. Particularly if you’re using LED gro lights, which don’t emit as much heat. Instead, use intake air from inside your home. This air is warmer.

Air from inside your home is also much higher in CO2 (because humans exhale CO2 when breathing). CO2 levels inside your home can be as high as 800ppm, which is almost twice as high outside air!

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