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The best grow room temperatures for optimal yield

Here at Grown-Up Hydroponics we want to help you produce the best yield you can, not just by providing fantastic products and nutrients, but by giving you expert advice as well.

So, we’re launching a new blog initiative, where you can ask us anything you want to know about growing, from equipment issues to nutrients, and different tips techniques to get the best out of your crop.

Simply use leave a comment below, message or comment via our Facebook page, or tweet us your questions, and we will pick the subjects that are either most popular, or we believe will be most useful, and will answer those in future blogs.

We’re kicking off the initiative with a topic we regularly get asked at Grown-Up Hydroponics – what is the ideal grow room temperature and how should I manage it?

Ideal temperature

Getting the temperature of your indoor garden correct is one of the most fundamental aspects of growing. Temperature directly influences humidity, so getting it wrong can have catastrophic effects on the growing environment. Excessive heat for example, will make your plants lose water quickly, releasing it into the atmosphere. If the temperature is too low, plants cannot absorb nutrients at the rate required for growth, so will not develop properly.

Photosynthesis can only occur within a certain temperature range too, so if your grow room is outside of that, expect no growth at all.

It goes without saying that the ideal temperature for your grow room will vary with what you’re growing. That said, there are some baselines from which you can work, and then experiment with until you find the perfect temperature for your set up. These include:

  • Clones and seedlings – 22oC to 28o
  • Vegging stage – 20oC to 25o
  • Flowering stage – 20oC to 25o

These temperatures are a good starting point and most plants will do fine in this range. But experiment with successive crops to discover which temperature produces optimum yields, and then stick to that as closely as you can.

Managing the temperature

So, you’ve established the optimum temperature to grow at, but how do you accurately retain that temperature in the face of fluctuating external temperatures and through your lights on/lights off phases?

Well, without wanting to sound too obvious, the first thing you will need is a thermometer to enable you to keep an accurate track on the temperature (you can browse our selection of thermometers and hygrometers here).

How you manage the temperature will depend on whether you use a grow tent or you are using a room in your house for growing.

By using a room in your house, you will have to be more proactive in managing temperature as it will be subject to greater fluctuation. This is because your walls are unlikely to be sufficiently well insulated to be able to maintain the temperature at a constant level required for consistent growth. As the outside temperature changes, both between daytime and night and across the seasons, the temperature of your grow room will also change.

A grow tent, to a large extent, mitigates against this issue by providing a more easily controlled environment for your plants. They come in all shapes and sizes, meaning you’re not restricted by the size of the crop you want to grow.

Heat from lighting

The majority of heat in your grow room is a by-product of the high-intensity lighting required to stimulate photosynthesis in the day cycle. Managing this source of heat is a major factor in maintaining a steady temperature.

A common way of achieving that is via an oscillating fan (see here for our range) which moves the warm air under the lighting away from the plants and mixes it with cooler air in the rest of the room to maintain a constant ambient temperature.

Another effective way of keeping the temperature even is to fit an extractor fan, which removes excess heat from your grow room altogether. This is particularly effective if you’re growing large crops with a significant lighting requirements and oscillating fans cannot reduce the temperature as much as is needed.

For dynamic control of your grow room when the lights are on, add in a fan controller. This handy piece of kit can be set to a specific temperature and alters the fan speed in relation to the ambient temperature, keeping it within tight boundaries.

Lights off at bedtime!

Part of the art and science of good growing is keeping a low temperature differential (TDIFF) between day and night. The challenge, therefore, is to keep the temperature high enough come bedtime when the lights go out, so plant development is not impaired.

One tip which can work for this is to reverse the light/dark phases, turning the lights on at night time when the temperature is lower outside, and off in the day time when it is warmer outside.

Other than that, heaters combined with a good thermostat are the best solution. Simple tube heaters can provide a cost-effective solution to falling grow room temperatures, although more expensive heaters are available if required.

If you’re using a grow tent, ensuring it is insulated well can help maintain a low TDIFF, as will taking in air from another room rather than directly from outside.

Don’t forget your nutrients

One aspect of temperature control that many growers forget is storing nutrients. Nutrients should be stored between 18oC and 21oC and away from direct sunlight. If allowed to get very cold, below 5oC, then crystallisation can occur, which will render the product unusable. But it doesn’t need to get down to those temperatures for your nutrients to have a detrimental effect on your plants. Cold nutrients can lower the temperature of the grow medium, and therefore the root zone of the plant, leading to poor absorption of nutrients.

So, there’s a brief introduction to how to manage grow room temperatures. If you would like further advice, please drop us a line. If you have any questions about any aspects of growing, please leave us a comment below or on our social media channels.

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